INSTRUCTION MANUAL

Sound Level Meter

NL-20

3-20-41 Higashimotomachi, Kokubunji, Tokyo 185-8533, Japan

www.64817.com TEL:0756-2236929
 Organization of the NL-20 Documentation

The documentation for the Sound Level Meter NL-20 consists of three sepa-
rate manuals.

Instruction Manual (this document)

Describes operating procedures for the Sound Level Meter NL-20, connec-
tion and use of peripheral equipment such as a level recorder and printer.

Serial Interface Manual

Describes how to use the serial interface built into the Sound Level Meter
NL-20. The manual covers the communication protocol, use of control
commands for the sound level meter, format of data output by the sound
level meter, and other topics.

Technical Notes
This document provides in-depth information about the circuit configura-
tion and performance of the sound level meter, microphone construction
and characteristics, influence of extension cables and windscreen on the
measurement, and other topics.

* Company names and product names mentioned in this manual are usu-
ally trademarks or registered trademarks of their respective owners.

i
 Organization of This Manual

This manual describes the features, operation and other aspects of the Sound
Level Meter NL-20

The manual contains the following sections.

Outline
Gives basic information about the configuration and features of the unit,
and also contains a block diagram.

Controls and Functions

Briefly identifies and explains the controls and connectors and all other
parts of the unit.

Preparations
Gives information about power supply, pre-use checks, installation, con-
nections, key settings etc.

Reading the Display

Explains the symbols and other information appearing on the display of
the unit.

Power On/Off
Explains how to turn the unit on and off.

Measurement
Explains how to perform measurement.

Store Operations
Explains how to store measurement results in the memory of the unit.

Default Settings
Lists the factory default settings of the unit.

ii
Output Connectors
Explains the output connectors of the unit.

Optional Accessories
Explains how to use external equipment for example to store measurement
data.

Specifications
Lists the technical specifications of the unit.

* All company names and product names mentioned in this manual are
trademarks or registered trademarks of their respective owners.

iii
 To conform to the EU requirement of the Directive
2002/96/EC on Waste Electrical and Electronic Equip-
ment, the symbol mark on the right is shown on the
instrument.

iv
 FOR SAFETY
In this manual, important safety instructions are specially marked as shown
below. To prevent the risk of death or injury to persons and severe damage
to the unit or peripheral equipment, make sure that all instructions are fully
understood and observed.

Caution D isrega rd i ng i nst r uct ions

printed here incurs the risk of
injury to persons and/or dam-
age to peripheral equipment.

Important
D isrega rd i ng i nst r uct ions
printed here incurs the risk of
damage to the product.

Note
Mentioned about the tips to
use this unit properly. (This
messages do not have to do
with safety.)

v
vi
 Precautions
Operate the unit only as described in this manual.
Protect the unit from shocks and vibration. Be especially careful not to
touch the microphone membrane to avoid damage. The membrane is an
extremely thin metal film which can be damaged easily.
Do not use the unit with a different microphone/preamplifier from the
one indicated on the name plate of the unit.
Ambient conditions for operation of the unit are as follows: temperature
range -10 to +50°C, relative humidity 10 to 90%.
Protect the unit from water, dust, extreme temperatures, humidity, and
direct sunlight during storage and use. Also keep the unit away from air
with high salt or sulphur content, gases, and stored chemicals.
Always turn the unit off after use. Remove the batteries from the unit if
it is not to be used for a long time. When disconnecting cables, always
grasp the plug and do not pull the cable.
Clean the unit only by wiping it with a soft, dry cloth or, when neces-
sary, with a cloth lightly moistened with water. Do not use any solvents,
cleaning alcohol or cleaning agents.
Do not try to disassemble the unit.
In case of an apparent malfunction, do not attempt any repairs. Note the
condition of the unit clearly and contact the supplier.
Do not tap the LCD panel or other surfaces of the unit with a pointed
object such as a pencil, screwdriver, etc.
Take care that no conductive objects such as wire, metal scraps, conduc-
tive plastics etc. can get into the unit.
To ensure continued precision, have the unit checked and serviced at
regular intervals.
When disposing of the unit, be sure to observe all applicable legal regula-
tions and guidelines in your country and community.

vii
viii
Quantifier Notation of Sound Level Meter NL-20 According to
International Standards and JIS
(Excerpts from ISO 1996, 3891, IEC 61672-1, JIS Z 8202, 8731)

ix
 Contents
Organization of the NL-20 Documentation ..................................... i
FOR SAFETY.................................................................................v
Precautions................................................................................... vii
Quantifier Notation of Sound Level Meter NL-20
According to International Standards and JIS .................... ix
Outline ............................................................................................1
Controls and Functions ...................................................................3
Front View .................................................................................3
Operation Keys ..........................................................................4
Bottom View..............................................................................7
Rear View ..................................................................................8
Preparations ....................................................................................9
Power Supply ............................................................................9
Windscreen (WS-10) ................................................................12
Tripod Mounting ......................................................................12
Microphone Extension Cables (EC-04 series) ..........................13
Connection to a Printer (DPU-414, CP-11, CP-10) ...................15
Connection to a Level Recorder
(LR-06, LR-07, LR-04, LR-20A).................................... 18
Connection to a Computer ....................................................... 18
Measurement in Dark Locations ..............................................19
LCD Contrast ..........................................................................20
Calibration ............................................................................... 21
Reading the Display ......................................................................28
Display screen .........................................................................28
Menu screens .........................................................................32

x
Power On/Off ................................................................................36
Measurement .................................................................................38
Sound level Measurement ........................................................38
Equivalent Continuous Sound level (LAeq) Measurement ......... 41
Sound Exposure Level (LAE) Measurement .............................46
Maximum (Lmax) and Minimum (Lmin)
Sound level Measurement ................... 51
Percentile Sound level (LN) Measurement ................................56
Back-Erase Function ................................................................62
Store Operations ...........................................................................63
Default Settings .............................................................................68
Output Connectors ........................................................................69
AC Output ..............................................................................69
DC Output ...............................................................................70
I/O Connector .......................................................................... 71
Optional Accessories .....................................................................72
Microphone Extension Cables EC-04 Series ............................72
Printer DPU-414/CP-11/CP-10 .................................................73
Level Recorder LR-06/LR-07/LR-04/LR-20A .........................76
Specifications ................................................................................78

xi
xii
 Outline
The Sound Level Meter NL-20 complies to IEC and JIS standards. In addi-
tion to the regular noise and sound level measurements of conventional sound
level meters, it also incorporates the following measurement functions.

Sound level Lp
Equivalent continuous sound level L eq
Sound exposure level LE
Maximum sound level L max
Minimum sound level L min
Percentile sound level L N (five selectable settings)

Measurement settings and results (level values and bar graph) are shown on
the backlit LCD panel.

Measurement data (sound level, processed data, measurement parameters)

can be stored in the internal memory of the unit . The serial interface allows
sending measurement data to a printer or computer.

The following accessories are optional, to cover a wide range of application

requirements.
Printer DPU-414
Serves to produce hard copy of measurement data (including data
stored in memory).
Level recorder LR-07, LR-20A
Serves to record sound level changes over time.

1
Outline

MIC / Preamp A C
AMP 1 AMP 2 AMP 3

FLAT FLAT

CAL.SIG.

OVER LOAD DET. AMP 4

A/D
D/A
CONV.
AMP 5

V ref.

DC OUT
AMP 8 AMP 10

AC DC OUT
AC OUT

DATA BUS

ADDRESS BUS
CPU DSP
DATA BUS

Start Pause
Stop Store Mode Cont
ADDRESS BUS

A C FLAT Fast Slow

Menu Down Page Up Range KEY SW

Recall Recall data Cal adj

LCD
Light Print Cal

E2PROM RS-232-C
Power

POWER SUPPLY

NL-20 Block Diagram

2
 Controls and Functions
Front View

Microphone/preamplifier

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Display

Start Pause
Stop Store Mode Cont

A C FLAT Fast Slow Operation Keys

Menu Down Page Up Range
Recall Recall data Cal adj

Hand strap Light Print Cal

NL-20 Power

SOUND LEVEL METER

Microphone/preamplifier
The microphone and preamplifier are configured as an integrated
assembly. The assembly can be removed from the sound level meter and
connected via an optional extension cable, for measurements a distance.

Display
This backlit LCD shows the sound level as a numeric reading and a bar
graph. The display also shows the operation mode of the sound level
meter, the selected measurement parameters, warning indications etc.

Hand strap
Makes the unit easy to carry and hold on your palm.

3
Controls and Functions

Operation Keys

Start Pause
Stop Store Mode Cont

A C FLAT Fast Slow

Menu Down Page Up Range

Recall Recall data Cal adj

Light Print Cal

Power
NL-20
SOUND LEVEL METER

Start/Stop key
Press to start or stop the sound level measurement (including the various
processing functions).

Store key
Press to store measurement data in memory.

Mode key
This key is used for reading the measurement results. With each push
of the button, the display format is switched according to the processing
types selected from the menu.

Pause/Cont key
During a measurement, this key can be used to exclude unwanted portions
from processing. Pressing the key again causes processing to be resumed.
It is also possible to use the key for excluding an interval of up to 5 seconds
before the key was pressed.

4
 Controls and Functions

Menu key
When this key is pressed, the menu screen 1/3 appears on the display.
Pressing the key again switches the display back to the original condition.
Menu pages are switched with the Page Down Up keys to the right of
the key.

A/C/FLAT key
Sets frequency weighting to A, C or FLAT.

Fast/Slow key
Sets the time weighting to Fast or Slow.

Range , keys
Select the level range for the measurement.
The following six settings are available:
20 to 80, 20 to 90, 20 to 100, 20 to 110, 30 to 120, 40 to 130

Recall key
Serves to recall data stored in the memory of the unit.

Recall Data , keys

When the display shows the measurement screen, these keys select the
data number in which to store data next.
When the display shows data from memory, the keys select the data
number to be displayed.

Light key
This key activates the backlight for easier viewing of the display in
low-light conditions. To turn the backlight off, press the key once more.
When the automatic light out function was selected from the menu, the
light will turn itself off automatically after 5 minutes.

5
Controls and Functions

Print key
When the optional printer DPU-414, CP-11, or CP-10 is connected,
pressing this key initiates a printout.

Cal key
Pressing this key activates the built-in oscillator for electrical calibration
of the NL-20 or for level matching of the unit and connected equipment.

Power key
Turns the unit on and off when you hold the key down for more than 1
second.

Hand strap
Attach the Hand strap to the unit as shown below. The strap makes it
easier to carry the unit and serves as a precaution against dropping it.
Pass the strap over your wrist, as shown in the illustration.

Hand strap
attachment notch

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Hand strap

Using the hand strap

6
 Controls and Functions

Bottom View

AC DC I O
OUT

POWER

Cover
I/O connector
AC/DC output jack
External power supply jack

Cover
This cover protects the connectors on the bottom during transport or
storage. Removing the cover gives access to the connectors shown above.

External power supply jack

The optional AC adapter NC-98A, NC-98B or NC-34 series can be con-
nected here for powering the unit from an AC outlet.

Important
To prevent the risk of damage, do not use any
AC adapter other than the specified type.

AC/DC output jack

The signal selected on menu screen 3/3 is output here.
AC: AC signal (with frequency weighting)
DC: DC signal corresponding to sound level

I/O connector
This input/output connector serves for input of control signals and input/
output of measurement data. A printer, level recorder, or computer can
be connected here.

7
Controls and Functions

Rear View

Tripod mounting thread

The unit can be mounted on a camera tripod using this thread.

Battery compartment
Four batteries (IEC R6P, size AA) are inserted here.

8
 Preparations
Power Supply
The unit can be powered by four IEC R6P (size AA) batteries (alkaline or manganese)
or by the specified optional AC adapter (NC-98A, NC-98B or NC-34 series).
It is possible to use size AA rechargeable batteries, but a separate recharger
must be provided for such batteries, since the unit is not designed to recharge
batteries.
Before inserting or replacing the batteries and before connecting the AC
adapter, be sure to turn power to the unit off.

Note
When the AC adapter is connected, the unit will be
powered from the adapter, also when batteries are
inserted. (The AC adapter has priority.)
In case of a power failure or other interruption of AC
power, the unit will automatically switch to battery
power and continue to operate.

9
Preparations

Inserting the batteries

1. Lightly press the cover of the battery compartment and slide it to the
right.
2. Insert the four IEC R6P batteries, paying attention to the polarity as
indicated in the compartment.
3. Replace the cover.
Lightly press hare and
slide to the right

IEC R6P
(size AA)
battery

The life of a set of batteries depends on usage conditions and various other
factors. Some reference values are shown below.

Continuous use
Alkaline batteries LR6 Approx. 34 hours
NL-20
Manganese batteries R6P Approx. 14 hours

When display backlighting is used, battery life will be about half of the
above values.
When auxiliary processing is ON, battery life will be about 20 percent shorter.

Important
Take care not to reverse the (+) and (-) polarity
when inserting the batteries.
Always replace all four batteries together.
Do not mix old and new batteries or batteries
of different type.
Remove the batteries from the unit, if the unit
is not to be used for a month or longer.

10
 Preparations

AC adapter (option)
Connect the AC adapter as shown below.

Important
To prevent the risk of damage, do not use any
AC adapter other than the NC-98A, NC-98B
or NC-34 series (both available as options).

11
Preparations

Windscreen (WS-10)
When making outdoor measurements in windy weather or when measuring air
conditioning equipment or similar, wind noise at the microphone can cause
measurement errors. Such effects can be reduced by using the windscreen WS-10.
For information on the influence of the windscreen on wind noise etc., please
refer to the separate Technical Notes.

Windscreen WS-10

Tripod Mounting
For long-term measurements, the unit can be mounted on a camera tripod.
Proceed carefully, to avoid dropping the unit or tipping over the tripod.

Tripod mounting thread

12
 Preparations

Microphone Extension Cables (EC-04 series)

Turn power to the unit off before separating the microphone from the main unit.
To reduce measurement deviations due to refraction effects and the acoustic
influence of the operator, the microphone can be detached from the unit and
connected via an extension cable. Optional cables are listed in the table below.

Extension cable EC-04 series

Model Length Model Length

EC-04 2m EC-04C 30 m (reel) + 5 m (connection cable)
EC-04A 5m EC-04D 50 m (reel) + 5 m (connection cable)
EC-04B 10 m EC-04E 100 m (reel) + 5 m (connection cable)

It is also possible to connect several cables in series.

Important
With long extension cables, the cable capaci-
tance restricts the upper measurement frequency
and measurement level. For details, please refer
to the Technical Notes.

1. Loosen the preamplifier fastening screw and remove the preamplifier

from the main unit.

Microphone
Sound level meter
main unit

Preamplifier
Fastening screw

Important
Never separate the microphone and preampli-
fier, because this can lead to damage.

13
Preparations

2. Connect the extension cable to the preamplifier and to the main unit
and fasten the connectors with the fastening screw.
3. When mounting the microphone on a tripod, first fasten the microphone
holder (supplied with the extension cable) to the tripod. Then insert
the extension cable connector into the microphone holder.

Microphone Connector

Microphone
Microphone holder extension cable

Tripod

14
 Preparations

Connection to a Printer (DPU-414, CP-11, CP-10)

The I/O port on the bottom of the unit can be used for connection of an
optional printer (DPU-414, CP-11, CP-10). Use the optional printer cable
CC-93 to connect the I/O port of the unit to the serial input of the printer.

AC DC I O
OUT
I/O connector
POWER

To serial input of printer

DPU-414/CP-11/CP-10

Printer cable CC-93

15
Preparations

Setting the software DIP switches of the DPU-414

Turn on the power while holding down the ON LINE key of the DPU-414. A
printout showing the current status of the printer is produced.
An example showing suitable software DIP switch settings for use of the printer
with the NL-20 is shown below. (The actual printout will be in a different font.)

Continue ? : Push’ On-line SW’

Write ? : Push’ Paper feed SW’
Dip SW-1
1 (OFF) : Input = Serial
2 (ON) : Printing Speed = High
3 (ON) : Auto Loading = ON
4 (OFF) : Auto LF = OFF
5 (ON) : Setting Command = Enable
6 (OFF) : Printing
7 (ON) : Density
8 (ON) : 100 %

Continue ? : Push’ On-line SW’

Write ? : Push’ Paper feed SW’
Dip SW-2
1 (OFF) : Printing Columns = 80
2 (ON) : User Font Back-up = ON
3 (ON) : Character Select = Normal
4 (ON) : Zero = Normal
5 (ON) : International
6 (ON) : Character
7 (ON) : Set
8 (ON) : =Japan

Continue ? : Push’ On-line SW’

Write ? : Push’ Paper feed SW’
Dip SW-3
1 (ON) : Data Length = 8 bits
2 (ON) : Parity Setting = ON
3 (OFF) : Parity Condition = Even
4 (OFF) : Busy Control = XON / XOFF
5 (OFF) : Baud
6 (ON) : Rate
7 (ON) : Select
8 (OFF) : = 19200 bps
Continue ? : Push’-line SW’
Write ? : Push’ Paper feed SW’
For details, please refer to the
documentation of the DPU-414.
DIP SW setting complete !! Set the baud rate of the sound
level meter to 19200 bps.

16
 Preparations

Setting the software DIP switches of the CP-11/CP-10

Set the DIP switches of the printer as follows.

DIP switch bank 1 DIP switch bank 2

(8 switches) (8 switches)
CP-11 ON ON

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

DIP switch bank 1 DIP switch bank 2

(8 switches) (6 switches)
CP-10 ON ON

1 2 3 4 5 6 7 8 1 2 3 4 5 6

Important
The switch marked with an asterisk (switch 6 of
DIP switch bank 2) serves for setting the transfer
speed. The ON position means 4800 bps and
the OFF position 9600 bps. This setting must
match the setting of the unit.

Switches 7 and 8 of DIP switch bank 2 of printer

CP-11 are set at the factory and should not be
changed. Otherwise, correct printing may not
be possible.

17
Preparations

Connection to a Level Recorder (LR-06, LR-07, LR-04, LR-20A)

Sound level recording
Connect the AC/DC output on the bottom of the unit to the level recorder,
as shown below.

Connection to a Computer
Connect the I/O port on the bottom of the unit to the RS-232-C interface of
the computer, using the optional interface cable.

For details, please refer to the Serial Interface Manual.

AC DC I O
OUT

I/O connector
POWER

Interface cable CC-92

To RS-232-C
interface connector
of computer

18
 Preparations

Measurement in Dark Locations

Pressing the Light key turns the display backlight on, making it easier to read
in dark locations. Pressing the key once more turns the light off.

Start Pause
Operation keys Stop Store Mode Cont

A C FLAT Fast Slow

Menu key
Menu Down Page Up Range
Recall data Cal adj
Function as Page Up/Down
keys when Menu key was
pressed Light Print Cal

Power
Light key NL-20
SOUND LEVEL METER

If the “Light Auto Off” item on the menu screen 3/3 is set to “5 min”, the
backlight turns itself off automatically after 5 minutes. When the item is set
to “Cont.”, backlighting is turned on and off with the Light key.

<I / O> 3/3

LCD Contrast : Cursor
Baud rate : 19200
Index : 1 Select with and keys
Output AC/DC : AC
Light Auto Off : 5min Light Auto Off
5 min / Cont.
Select with and keys
Menu screen 3/3

When the backlight is used continuously, battery life will be shortened to

about half.

19
Preparations

LCD Contrast
You can adjust the contrast of the display.
1. Press the Menu key.
The display changes to the menu screen.
2. Use the Page Up/Down keys to switch to menu screen 3/3.
3. Use the and keys to move the cursor to the LCD Contrast marks.
(The display is shown in reverse.)
4. Increase or decrease number of marks with and keys to adjust
contrast

Start Pause
Operation keys Stop Store Mode Cont

A C FLAT Fast Slow

Menu key
Menu Down Page Up Range
Recall data Cal adj
Function as Page Up/Down
keys when Menu key was
pressed Light Print Cal

Adjust contrast with

Power
and keys NL-20
SOUND LEVEL METER

Cursor
<I / O> 3/3 Select with and keys
LCD Contrast :
Baud rate :1
Index : Increase or decrease
Output AC/DC : AC
Light Auto Off : 5min number of marks
with and keys
to adjust contrast
Menu screen 3/3

5. Press the Menu key again to return to the measurement screen.

20
 Preparations

Calibration
Before starting a measurement, the unit must be calibrated. There are two types of
calibration: electrical calibration and acoustic calibration using a pistonphone.
Normally, electrical calibration only is required.

Electrical calibration
The built-in oscillator (1 kHz, sinusoidal wave) is used for electrical calibra-
tion.
1. Turn the unit on by pressing the Power key.
2. Use the Level Range and keys to select the 30 to 120 dB range.
3. Press the Menu key to bring up the menu display.
4. Use the Page Up/Down keys to show menu screen 1/3.
Verify that the Cal Mode is set to “Internal”.
If “External” is shown, use the and keys to move the cursor to
“External” and use the and keys to set it to “Internal”.

21
Preparations

5. Press the Menu key again to return to the measurement screen.

Press the Cal key. The display becomes as shown below.

If the level range is not set to 30 to 120 dB, the indication of 114 dB
flashes, and the required calibration value is 6 dB under the range
maximum. For example, if the level range is set to 130 dB, the
indication of 124 dB flashes.

6. Use the and keys to set the level display to 114.0 dB.

INT Cal 114 dB is shown

Set level range to 30 to 120

30 INT Cal 114dB 120

Set level display to 114.0 dB

with and keys

Cal screen
Frequency weighting automatically becomes Lc

Frequency weighting is temporarily set to “C”. When the Cal key is

pressed again, the original settings are restored.

22
 Preparations

Signal output for calibration of external equipment

The normal level range for calibration is 30 to 120 dB, but in order to allow
calibration of external equipment, calibration can also be performed at other
level range settings (Press the Level Range keys). In this case, the “XX dB”
indication of the calibration value flashes.
Perform the setting so that the calibration value is 6 dB under the maximum
of the selected range.
In this case, the AC output or DC output is used to calibrate connected
equipment.
1. Use the and keys to set the level indication to the calibration
value (maximum -6 dB).
2. Press the Cal key again to return to normal measurement mode.

The indication of 94 dB flashes.

Level range

20 INT Cal 94dB 100

Level indication

Cal screen

Note
Calibration cannot be performed if the unit is in a
measurement mode other than sound level measurement
(including triangle mark flashing in top left of screen,
and pause). Perform calibration after measurement
is completed (Start/Stop key was pressed).

23
Preparations

Acoustic calibration with sound calibrator NC-74 or pistonphone NC-72A

For acoustic calibration, the Rion sound calibrator NC-74 or pistonphone
NC-72A is mounted to the microphone of the sound level meter, and adjust-
ment is performed so that the reading of the meter is equal to the sound level
inside the coupler.

Important
Be very careful when inserting and removing the
microphone to and from the coupler, to avoid a
sudden pressure buildup which could destroy
the membrane of the microphone.
1. Turn off the sound calibrator or the pistonphone.
2. Turn on the NL-20.
3. Press the Menu key to bring up the menu display.
4. Use the Page Up/Down keys to show menu screen 1/3.
Verify that the Cal Mode is set to “External”.
If “Internal” is shown, use the and keys to move the cursor to
“Internal” and use the and keys to set it to “External”.

24
 Preparations

5. Press the Menu key again to return to the measurement screen.

6. Use the Level Range and keys to select the 30 to 120 dB range.
If the level range is not set to 30 to 120 dB, the EXT Cal indication
flashes.

EXT Cal flashes if level

range is not 120 dB

Level reading
20 EXT Cal 110

Cal screen

25
Preparations

7. Press the Cal key.

8. Mount the 1/2-inch adapter on the coupler of the NC-74 or NC-72A.

1/2-inch adapter NC-74-002

for NC-74

Sound calibrator NC-74 Pistonphone NC-72A

1/2-inch adapter
for NC-72A

9. Insert the microphone very carefully and slowly all the way into the
coupler.
10. Set the power switch of the sound calibrator or the pistonphone to ON.
11. Use the and keys to adjust the reading to 93.9 dB if the NC-74
is used, or to the value indicated on the pistonphone if the NC-72A
is used.

EXT Cal is shown

30 EXT Cal 120 30 EXT Cal 120

Cal screen

Level indication when NC-74 is used Level indication when NC-72A is used
(displayed sound pressure level of NL-20) (correct figure is indicated on NC-72A)

26
 Preparations

12. Turn off the sound calibrator or the pistonphone and NL-20.
13. Remove the microphone very carefully and slowly from the coupler.

Note
For details on operation of the NC-74 or NC-72A,
please refer to the instruction manual for them.
For information about compensation for atmospheric
pressure, please refer to the documentation of the
pistonphone NC-72A.

The NC-74 is designed to produce 94.0 dB under its

rated conditions, but in actual calibration, the sound
field compensation value which depends on the sound
level meter must be taken into consideration. For the
NL-20, adjust the reading to 93.9 dB.

27
 Reading the Display
Display screen
The illustration below is for demonstration purposes only. In actual use, not
all display elements will be visible at the same time, and the size and font
of the display may differ.

Indicates 100 hours have elapsed

For 200 hours, "2" is shown
Elapsed time indicator
Recall indicator
Measurement time indicator Start Start indicator
Battery capacity indicator Stop Stop indicator

Measurement symbol 99 Memory address display

Pause symbol E Store
20 Start 80 Level range indicator
Back-erase ON indicator Bar graph
Un Fast Ov Over-range indicator
Under-range indicator Level reading
Frequency weighting
Indicator
Time weighting indicator

Measurement symbol
Flashes while a measurement is in progress and while data are being
stored in memory.

Pause symbol
Lights up when processing or storing is paused. In the paused condition,
the sound level reading is not updated but bar graph is updated.

28
 Reading the Display

Battery capacity indicator

When operating the unit on batteries, periodically check this indicator to
determine the remaining battery capacity. The number of black segments
decreases as the batteries are used up. When the display starts to flash, correct
measurement is no longer possible. Replace the batteries with a fresh set.
The indicator is also displayed while the unit is powered from the AC adapter.

Batteries Batteries partly Flashing

good depleted Replace batteries

Measurement time indicator

Shows the selected measurement time. If no measurement time was
selected (arbitrary measurement time), the indication is blank.
The following measurement time settings are possible:
10 s (seconds), 1 m (minute), 5 m, 10 m, 15 m, 30 m, 1 h (hour), 8 h, 24
h, None

Recall indicator
Lights up when data stored in memory are being displayed.

Elapsed time indicator

During processing and memory store, this indicator shows the elapsed
time in seconds. If the time has exceeded 100 hours, the top digit of the
address indicator shows “1”.

Start indicator
This indicator appears for 1 second at measurement start.

Stop indicator
This indicator appears for 1 second at measurement stop.

Memory address display

Shows the memory address of stored data.

29
Reading the Display

Level range indicator

Shows the upper and lower limit of the bar graph. Make the setting that
is appropriate for the sound level.

Bar graph
Shows the sound level. The indication is updated every 100 milliseconds.

Over-range indicator (shown as Ov for sound level)

Shown when sound level overload has occurred.

Over-range indicator (shown as Ov for processed value)

Shown when any of the processed values contains an over-range level.
Lights up when over-range occurs during processing and stays lit until
the next processing measurement starts.

Level reading
Normally, this shows the sound level (updated every second).

Time weighting indicator

Shows the selected time weighting setting.

30
 Reading the Display

Frequency weighting indicator

Shows the selected frequency weighting setting.
L A: A weighting
L C: C weighting
L p: FLAT
The third and fourth digit are shown when processed values are displayed.
The meaning is as follows.
LAeq, L Ceq, Lpeq: Equivalent continuous sound level
LAE , L CE , LpE: Sound exposure level
LAmax, L Cmax, Lpmax: Maximum sound level
LAmin, L Cmin, Lpmin: Minimum sound level
LA05, L C05, Lp05: 5% percentile sound level
LA10, L C10, Lp10 : 10% percentile sound level
LA50, L C50, Lp50 : 50% percentile sound level
LA90, L C90, Lp90 : 90% percentile sound level
LA95, L C95, Lp95: 95% percentile sound level

Under-range indicator (shown as Un for sound level)

Shown when the sound level has fallen below -2.6 dB of the level range
lower limit, or below the measurement range. Shown for at least one
second.

Under-range indicator (shown as Un for processed value)

Shown when any of the processed values contains an under-range level.
Lights up when an under-range condition occurs during processing and
stays lit until the next processing measurement starts.

Back-erase ON indicator
Lights up when the data back-erase function (page 62) is enabled.

31
Reading the Display

Menu screens
There are three menu screens numbered 1/3 through 3/3.

Menu screen 1/3

Meas. time (measurement time)

Use , keys to select the measurement time.
Manual 10 sec 1 min 5 min 10 min 15 min 30 min
1 hour 8 hours 24 hours Manual ...

Back Erase (data exclusion function)

This function allows excluding the last 5 seconds before activation of
the pause condition from processing.
Off: Normal pause function
5 sec: 5 seconds preceding pause are excluded

Cal mode (calibration mode)

Internal: Select this position for electrical calibration of the unit using
the built-in oscillator.
External: Select this position for acoustic calibration of the unit using
a pistonphone.

32
 Reading the Display

Manual Data Clear

Determines whether stored data are to be cleared or not. When “On” is
selected, the indication “ OK Start Cancel Pause “ is shown on the
next line. To clear the data, press the [Start] key. To cancel the process
and return to the previous menu screen (1/3), press the Pause key.

Menu screen 2/3

Leq: Equivalent continuous

sound pressure level
<Display> 2/3 LE: sound exposure level
Leq : On L : Off Lmax: Maximum value
LE : Off L : Off
Lmax : Off L : On
Lmin: Minimum value
Lmin : Off L : Off LIST: List display
LIST : On L : Off LN: Percentile sound
T-L : On pressure level
T-L: Time/Level
Menu screen 2/3

Leq (Equivalent continuous sound level)

Set to “On” if the processing result is to be displayed, otherwise set to “Off”.

LE (Sound exposure level)

Set to “On” if the processing result is to be displayed, otherwise set to “Off”.

Lmax (Maximum value), Lmin (Minimum value)

Set to “On” if the processing result is to be displayed, otherwise set to “Off”.

LIST (List display)

Set to “On” if the processing result is to be displayed, otherwise set to “Off”.

LN (Percentile sound level)

Can be set from L01 to L99.
Set to “On” if the processing result is to be displayed, otherwise set to “Off”.

T-L (Time/Level)
Set to “On” if the processing result is to be displayed, otherwise set to “Off”.

33
Reading the Display

Menu screen 3/3

<I / O> 3/3

LCD Contrast : LCD Contrast
Baud rate : 19200 Baud rate
Index : 1
Output AC/DC : AC
Index
Light Auto Off : 5min Output AC / DC
Light Auto Off

Menu screen 3/3

LCD Contrast
The number of symbols corresponds to the contrast setting. It can be
changed with the and keys.

Baud rate (I/O transfer speed)

You can select 4800 bps, 9600 bps or 19200 bps with the and keys.

Index
This is a number identifying the unit when multiple units (up to 255)
are used.

Output AC/DC
Selects whether an AC or DC signal is output from the I/O connector.

Light Auto Off

Controls the automatic backlight turn-off function. When set to “Cont.”,
backlight on/off is controlled only by the Light key and is not automatically
turned off.

34
 Reading the Display

Measurement screen examples

m Manu
E
20 start 80

Fast

Sound pressure level example

m
A Fast

Leq : 55.5 L05 : 59.7

LE : 65.4 L10 : 57.8
Lmax : 78.9 L50 : 55.4
Lmin : 42.3 L90 : 52.1
LCeq : 58.9 L95 : 50.0 List display example

m Manu
A Fast
80

10 20s
59.1
T-L (time level) display example

35
 Power On/Off
Power-on
Turn the unit on by holding down the Power key for at least one second. When
the power-on screen appears, release the Power key. After the initial screen
was shown, the unit switches to the measurement screen.

Start Pause
Stop Store Mode Cont

A C FLAT Fast Slow

Menu Down Page Up Range

Recall Recall data Cal adj

Light Print Cal

Power key
Power
NL-20
SOUND LEVEL METER

SOUND LEVEL METER

NL-20

RION CO.,LTD.

Power-on screen

36
 Power On/Off

Power-off
Turn the unit off by holding down the Power key for at least one second.
When the power-off screen appears, release the Power key.

See You

Power-off screen

Note
Wait at least 5 seconds after turning the unit off
before you turn it on again.

37
 Measurement
When using this unit in a mode other than sound level measurement, all
processing functions provided by the unit are carried out simultaneously. For
example, when equivalent continuous sound level measurement is selected,
the sound exposure level and percentile level are also determined. However,
the time percentage setting for the percentile level (5 values) must be selected
beforehand.

Sound level Measurement

The procedure for sound level measurement is described below.
Preparations as described in the previous chapter must be completed fi rst.

Sound level
1. Turn the unit on by pressing the Power key.
After the power-on screen, the measurement screen is shown.
The various settings depend on the condition the unit was in before
it was last turned off.

SOUND LEVEL METER

NL-20

RION CO.,LTD.

Power-on screen

38
 Measurement

Start Pause
Stop Store Mode Cont Pause/Cont key

A/CFLAT key A C FLAT Fast Slow

Fast/Slow key

Menu Down Page Up Range

Recall Recall data Cal adj Range keys

Light Print Cal

Power key
Power
NL-20
SOUND LEVEL METER

2. Select the frequency weighting with the A/C/FLAT key. For normal
sound level measurements, select the “A” setting.
If “Lp” (FLAT) is selected, the sound level from 20 Hz to 8 kHz can
be measured.
3. Use the Fast/Slow key to select the time weighting (dynamic
characteristics). Normally, the “Fast” setting should be used.
4. When performing measurements according to IEC or other standards,
the frequency weighting and time weighting setting required by the
standard should be selected.
5. Use the Level Range keys to select the level range. Choose a setting in
which the bar graph indication registers to about the middle of the range.
If the “ Ov ” (Over) or “ Un ” (Under) indicators light up frequently,
change the level range setting.

m Manu
Select time weighting
with Fast/Slow key 20 80 Level range
Bar graph
Fast
Level reading
Select frequency weighting
with A/C/FLAT key
Measurement screen

39
Measurement

m Manu

30 120

Under-range Un Fast Ov Over-range

signal indicator signal indicator

Measurement screen

6. The numeric level indication shows the currently measured sound

level. The reading is updated once every second.
The Pause/Cont key can be used to stop and start the level reading
from being updated. The bar graph indication is updated during pause
condition. In the pause condition, a mark appears on the display.
Pressing the Pause/Cont key once more resumes the measurement.

m Manu
Flashing during measurement
Pause mark 30 120

Fast

Measurement screen

Important
During sound level measurement, do not
press the Mode key because this causes
the processing results to be displayed. As
shown in the example, if the letter following “L”
is displayed without an appendix, sound level
measurement is being carried out.
L A ....... Display shows sound level.
L Aeq ..... Display does not show sound level.

40
 Measurement

Equivalent Continuous Sound level (LAeq) Measurement

The procedure for equivalent continuous sound level measurement is described
below.
Preparations as described in the previous chapter must be completed fi rst.
1. Turn the unit on by pressing the Power key.
2. Select the frequency weighting with the A/C/FLAT key. For normal
measurements, select the “A” setting.
When “C” (C weighting) is selected, the equivalent continuous sound
level (L Ceq) is measured.
3. Use the Fast/Slow key to select the time weighting. Normally, the
“Fast” setting should be used.

m Manu
Select time weighting
with Fast/Slow key 20 80 Level range
Bar graph
Fast
Level reading
Select frequency weighting
with A/C/FLAT key
Measurement screen

4. Use the Level Range keys to select the level range. Choose a setting in
which the bar graph indication registers to about the middle of the range.
If the “ Ov ” (Over) or “ Un ” (Under) indicators light up frequently,
change the level range setting.

m Manu

30 120

Under-range Un Fast Ov Over-range

signal indicator signal indicator

Measurement screen

41
Measurement

Start Pause
Stop Store Mode Cont Pause/Cont key

A/C/FLAT key A C FLAT Fast Slow Fast/Slow key

Menu key
Menu Down Page Up Range
Recall Recall data Cal adj Range keys
Pressing the Menu key enables
the Page Up/Down key function
Light Print Cal
A C FLAT Fast Slow
Power key
Power
Down Page Up
NL-20
SOUND LEVEL METER

Note
This unit uses high-speed sampling of the sound
pressure waveform for L eq and LE processing (30.3
μs). The result is therefore unaffected by dynamic
characteristics and accurate also for a short time
period.
5. Use the menu to set the measurement time.
Press the Menu key to call up the menu screen 1/3.
6. Use the and keys to move the cursor to the “Meas. time” item,
and use the and keys to select the measurement time.

Manual 10 sec 1 min 5 min 10 min 15 min 30 min

1 hour 8 hours 24 hours Manual ...

<System> 1/3
Meas. time : 10min Measurement time
Back Erase : Off
Cal mode : Internal
Manual data Clear : Off

Menu screen 1/3

42
 Measurement

7. Use the Page Up/Down keys to display the menu screen 2/3.
If L eq: Off is displayed, use the and keys to move the highlight
to “Off”, and use the and keys to set the item to “On”.

Leq : Set equivalent continuous

<Display> 2/3 sound level display to "On".
Leq : On L : Off
LE : Off L : Off
Lmax : Off L : On
Lmin : Off L : Off
LIST : On L : Off
T-L : On

Menu screen 2/3

8. To use the data exclusion (back-erase) function, please refer to page 62.

Note
In addition to the regular pause function it is also
possible to exclude (back-erase) data from the im-
mediately preceding 5 seconds.
9. Press the Menu key to return to the measurement screen.
10. Press the Start/Stop key to start the measurement.
During measurement, the symbol flashes and the elapsed measure-
ment time is displayed.

Measurement time Elapsed measurement time

m Manu
Measurement symbol
E
Pause symbol 20 Start 80

Fast

Measurement screen

43
Measurement

When the measurement time set in step 6 has elapsed, the measurement
terminates automatically. When wishing to terminate the measurement
earlier, press the Start/Stop key.
If Manual was selected, the Start/Stop key must be used to conclude
the measurement.
If an under-range condition or over-range condition occurs at
least once during measurement, the “ Ov ” (Over) or “ Un ”
(Under) indicator appears, to show that the processing data contain
over-range or under-range data.

Important
During measurement, most of the keys such
as the A/C/FLAT key and Level keys are in-
operative. Only the following four keys can be
used: Start/Stop, Pause/Cont, Mode, Light. All
other settings must be made before starting the
measurement.

During measurement, the Pause/Cont key can be used to pause and

resume the measurement. During pause, the pause symbol ( ) is shown.
(Any pause intervals and the back-erase time if data back-erase is
enabled are not included in the measurement time.)
If data back-erase was enabled in step 8, the data are indicated on
the display, as shown below.

Manu
A Fast
80

10 20s
Data range to be excluded
59.1
Measurement screen

44
 Measurement

11. When the measurement is completed, you can use the Mode key to
switch between various ways of displaying the measurement result.
When L Aeq is shown, the equivalent continuous sound level is
being displayed.
If LAeq is not shown, check whether LAeq on the menu screen 2/3 is
set to “On”.
If “ Ov ” (Over) is shown, the sound level data used for processing
contained over-range data.
If “ Un ” (Under) is shown, the sound level data used for processing
contained under-range data.

m Manu

30 120
Under-range
signal indicator Un Fast Ov Over-range
signal indicator
Equivalent continuous eq
sound pressure level
Measurement screen

Note
It is also possible to use the Mode key during mea-
surement to read the equivalent continuous sound
level up to that point. (This applies only to the nu-
meric level display. The bar graph indication shows
the sound level.)
Changing the A/C/FLAT or Fast/Slow setting after
measurement is completed has no effect on the dis-
played processing result.

45
Measurement

Sound Exposure Level (L AE) Measurement

The procedure for sound exposure level measurement is described below.
Preparations as described in the previous chapter must be completed first.
1. Turn the unit on by pressing the Power key.
2. Select the frequency weighting with the A/C/FLAT key. For normal
measurements, select the “A” setting.
3. Use the Fast/Slow key to select the time weighting (dynamic char-
acteristics). Normally, the “Fast” setting should be used.

m Manu
Select time weighting
with Fast/Slow key 20 80 Level range
Bar graph
Fast
Level reading
Select frequency weighting
with A/C/FLAT key
Measurement screen

4. Use the Level Range keys to select the level range. Choose a setting in
which the bar graph indication registers to about the middle of the range.
If the “ Ov ” (Over) or “ Un ” (Under) indicators light up frequently,
change the level range setting.

m Manu

30 120

Under-range Un Fast Ov Over-range

signal indicator signal indicator

Measurement screen

46
 Measurement

Start Pause
Stop Store Mode Cont Pause/Cont key

A/C/FLAT key A C FLAT Fast Slow Fast/Slow key

Menu key
Menu Down Page Up Range
Recall Recall data Cal adj Range keys
Pressing the Menu key enables
the Page Up/Down key function
Light Print Cal
A C FLAT Fast Slow
Power key
Power
Down Page Up
NL-20
SOUND LEVEL METER

Note
This unit uses high-speed sampling of the sound
pressure waveform for L eq and LE processing (30.3
μs). The result is therefore unaffected by dynamic
characteristics and accurate also for a short time
period.
5. Use the menu to set the measurement time.
Press the Menu key to call up the menu screen 1/3.
6. Use the and keys to move the cursor to the “Meas. time” item,
and use the and keys to select the measurement time.

Manual 10 sec 1 min 5 min 10 min 15 min 30 min

1 hour 8 hours 24 hours Manual ...
When Manual is selected, the measurement time is controlled by the
operator. The maximum time is 200 hours.

<System> 1/3
Meas. time : 10min Measurement time
Back Erase : Off
Cal mode : Internal
Manual data Clear : Off

Menu screen 1/3

47
Measurement

7. Use the Page Up/Down keys to display the menu screen 2/3.
If LE: Off is displayed, use the and keys to move the highlight
to “Off “, and use the and keys to set the item to “On”.

<Display> 2/3
Leq : On L : Off
LE : On L E : Set sound exposure
Lmax : Off L : On level display to "On".
Lmin : Off L : Off
LIST : On L : Off
T-L : On

Menu screen 2/3

8. To use the data exclusion (back-erase) function, please refer to page 62.

Note
In addition to the regular pause function it is also
possible to exclude (back-erase) data from the im-
mediately preceding 5 seconds.
9. Press the Menu key to return to the measurement screen.
10. Press the Start/Stop key to start the measurement.
During measurement, the symbol flashes and the elapsed measurement
time is displayed.

Measurement time Elapsed measurement time

m Manu
Measurement symbol
E
Pause symbol 20 Start 80

Fast

Measurement screen

48
 Measurement

When the measurement time set in step 6 has elapsed, the measurement
terminates automatically. When wishing to terminate the measurement
earlier, press the Start/Stop key.
If no display (arbitrary measurement time) was selected, the Start/
Stop key must be used to conclude the measurement.

Important
During measurement, most of the keys such
as the A/C/FLAT key and Level keys are in-
operative. Only the following four keys can be
used: Start/Stop, Pause/Cont, Mode, Light. All
other settings must be made before starting the
measurement.

During measurement, the Pause/Cont key can be used to pause and

resume the measurement. During pause, the pause symbol ( ) is
shown. (Any pause intervals and the back-erase time if data back-erase
is enabled are not included in the measurement time.)

If data back-erase was enabled in step 8, the data are indicated on

the display, as shown below.

Manu
A Fast
80

10 20s
Data range to be excluded
59.1
Measurement screen

49
Measurement

11. When the measurement is completed, you can use the Mode key to
switch between various ways of displaying the measurement result.
When LAE is shown, the sound exposure level is being displayed.
If LAE is not shown, check whether LAE on the menu screen 2/3 is
set to “On”.
If “ Ov ” (Over) is shown, the sound level data used for processing
contained over-range data.
If “ Un ” (Under) is shown, the sound level data used for processing
contained under-range data.

m Manu

30 120
Under-range
signal indicator Un Fast Ov Over-range
signal indicator
Sound Exposure Level E

Measurement screen

Note
It is also possible to use the Mode key during mea-
surement to read the equivalent continuous sound
level up to that point. (This applies only to the nu-
meric level display. The bar graph indication shows
the sound level.)
Changing the A/C/FLAT or Fast/Slow setting after
measurement is completed has no effect on the dis-
played processing result.

50
 Measurement

Maximum (Lmax) and Minimum (Lmin) Sound level Measurement

The procedure for maximum and minimum sound level measurement is
described below.
Preparations as described in the previous chapter must be completed fi rst.
1. Turn the unit on by pressing the Power key.
2. Select the frequency weighting with the A/C/FLAT key. For normal
measurements, select the “A” setting.
3. Use the Fast/Slow key to select the time weighting. Normally, the
“Fast” setting should be used.

m Manu
Select time weighting
with Fast/Slow key 20 80 Level range
Bar graph
Fast
Level reading
Select frequency weighting
with A/C/FLAT key
Measurement screen

4. Use the Level Range keys to select the level range. Choose a setting in
which the bar graph indication registers to about the middle of the range.
If the “ Ov ” (Over) or “ Un ” (Under) indicators light up frequently,
change the level range setting.

m Manu

30 120

Under-range Un Fast Ov Over-range

signal indicator signal indicator

Measurement screen

51
Measurement

Start Pause
Stop Store Mode Cont Pause/Cont key

A/C/FLAT key A C FLAT Fast Slow Fast/Slow key

Menu key
Menu Down Page Up Range
Recall Recall data Cal adj Range keys
Pressing the Menu key enables
the Page Up/Down key function
Light Print Cal
A C FLAT Fast Slow
Power key
Power
Down Page Up
NL-20
SOUND LEVEL METER

5. Use the menu to set the measurement time.

Press the Menu key to call up the menu screen 1/3.
6. Use the and keys to move the cursor to the “Meas. time” item,
and use the and keys to select the measurement time.

Manual 10 sec 1 min 5 min 10 min 15 min 30 min

1 hour 8 hours 24 hours Manual ...

<System> 1/3
Meas. time : 10min Measurement time
Back Erase : Off
Cal mode : Internal
Manual data Clear : Off

Menu screen 1/3

52
 Measurement

7. Use the Page Up/Down keys to display the menu screen 2/3.
If Lmax: Off, Lmin: Off is displayed, use the and keys to move the
highlight to “Off”, and use the and keys to set the item to “On”.

<Display> 2/3
Leq : On L : Off
LE : On L : Off
Lmax : Off L max : Set maximum sound
Lmin : On
LIST : On L : Off
level display to "On".
T-L : On

Menu screen 2/3 L min : Set minimum sound

level display to "On".

8. Press the Menu key to return to the measurement screen.

9. Press the Start/Stop key to start the measurement.
During measurement, the symbol flashes and the elapsed measure-
ment time is displayed.

Measurement time Elapsed measurement time

m Manu
Measurement symbol
E
Pause symbol 20 Start 80

Fast

Measurement screen

When the measurement time set in step 6 has elapsed, the measurement
terminates automatically. When wishing to terminate the measurement
earlier, press the Start/Stop key.
If no display (arbitrary measurement time) was selected, the Start/
Stop key must be used to conclude the measurement.

53
Measurement

Important
During measurement, most of the keys such
as the A/C/FLAT key and Level keys are in-
operative. Only the following four keys can be
used: Start/Stop, Pause/Cont, Mode, Light. All
other settings must be made before starting the
measurement.

During measurement, the Pause/Cont key can be used to pause and

resume the measurement. During pause, the pause symbol ( ) is
shown. (Any pause intervals and the back-erase time if data back-erase
is enabled are not included in the measurement time.)
10. When the measurement is completed, you can use the Mode key to
switch between various ways of displaying the measurement result.
When LAmax is shown, the maximum sound level is being displayed.
When LAmin is shown, the minimum sound level is being displayed.
If LAmax and LAmin are not shown, check whether L max and L min on
the menu screen 2/3 are set to “On”.
If an over-range or under-range condition has occurred at least once
during the measurement, the” Ov ” (Over) or “ Un ” (Under) indication
is shown on the display, to indicate that over-range or under-range
data were included in the sound level measurement values used for
processing.

m Manu

30 120
Under-range
signal indicator Un Fast Ov Over-range
signal indicator
Maximum (Lmax) max
Minimum (Lmin)
Measurement screen

54
 Measurement

Note
It is also possible to use the Mode key during mea-
surement to read the maximum or minimum sound
level up to that point. (This applies only to the nu-
meric level display. The bar graph indication shows
the sound level.)

Note
Changing the A/C/FLAT or Fast/Slow setting after
measurement is completed has no effect on the dis-
played processing result.

55
Measurement

Percentile Sound level (LN) Measurement

The procedure for percentile sound level measurement is described below.
Preparations as described in the previous chapter must be completed first.
1. Turn the unit on by pressing the Power key.
2. Select the frequency weighting with the A/C/FLAT key. For normal
measurements, select the “A” setting.
3. Use the Fast/Slow key to select the time weighting (dynamic char-
acteristics). Normally, the “Fast” setting should be used.

m Manu
Select time weighting
with Fast/Slow key 20 80 Level range
Bar graph
Fast
Level reading
Select frequency weighting
with A/C/FLAT key
Measurement screen

4. Use the Level Range keys to select the level range. Choose a setting in
which the bar graph indication registers to about the middle of the range.
If the “ Ov ” (Over) or “ Un ” (Under) indicators light up frequently,
change the level range setting.

m Manu

30 120

Under-range Un Fast Ov Over-range

signal indicator signal indicator

Measurement screen

56
 Measurement

Start Pause
Stop Store Mode Cont Pause/Cont key

A/C/FLAT key A C FLAT Fast Slow Fast/Slow key

Menu key
Menu Down Page Up Range
Recall Recall data Cal adj Range keys
Pressing the Menu key enables
the Page Up/Down key function
Light Print Cal
A C FLAT Fast Slow
Power key
Power
Down Page Up
NL-20
SOUND LEVEL METER

5. Use the menu to set the measurement time.

Press the Menu key to call up the menu screen 1/3.
6. Use the and keys to move the cursor to the “Meas. time” item,
and use the and keys to select the measurement time.

Manual 10 sec 1 min 5 min 10 min 15 min 30 min

1 hour 8 hours 24 hours Manual ...
When Manual is selected, the measurement time is controlled by the
operator. The maximum time is 200 hours.

<System> 1/3
Meas. time : 10min Measurement time
Back Erase : Off
Cal mode : Internal
Manual data Clear : Off

Menu screen 1/3

Important
Because sampling for LN is performed at 100 ms
intervals, a measurement time of 10 seconds
or less will not yield correct results.

57
Measurement

7. Use the Page Up/Down keys to display the menu screen 2/3.
8. In the default condition, the unit is set up to measure the percentile
sound level L5, L10, L50, L90, and L95. These settings can be changed
to any value between L1 and L99 (up to five settings).
Use the and keys to move the highlight and use the and keys
to change the time percentile number and to toggle the setting between
“On” and “Off”.

<Display> 2/3
Leq : On L : On
LE : On L : On
Lmax : Off L : On L N : Percentile sound level
Lmin : On L : Off
LIST : On L : On Set required L N to On.
T-L : On

L N can be set in the range from 1 to 99.

Menu screen 2/3

Important
Establish these settings before starting the
measurement. If a setting is changed later, the
measurement will be invalid.
9. To use the data exclusion (back-erase) function, please refer to page 62.

Note
In addition to the regular pause function it is also
possible to exclude (back-erase) data from the
immediately preceding 5 seconds.
10. Press the Menu key to return to the measurement screen.

58
 Measurement

11. Press the Start/Stop key to start the measurement.

During measurement, the symbol flashes and the elapsed measure-
ment time is displayed.

Measurement time Elapsed measurement time

m Manu
Measurement symbol
E
Pause symbol 20 Start 80

Fast

Measurement screen

When the measurement time set in step 6 has elapsed, the measurement
terminates automatically. When wishing to terminate the measurement
earlier, press the Start/Stop key.
If no display (arbitrary measurement time) was selected, the Start/
Stop key must be used to conclude the measurement.
If an over-range or under-range condition has occurred at least once
during the measurement, the“ Ov ” (Over) or “ Un ” (Under) indication
is shown on the display, to indicate that over-range or under-range
data were included in the sound level measurement values used for
processing.

m Manu

120

Under-range Un Fast Ov Over-range

signal indicator signal indicator

Measurement screen

59
Measurement

Important
During measurement, most of the keys such
as the A/C/FLAT key and Level keys are in-
operative. Only the following four keys can be
used: Start/Stop, Pause/Cont, Mode, Light. All
other settings must be made before starting the
measurement.

During measurement, the Pause/Cont key can be used to pause and resume
the measurement. During pause, the pause symbol ( ) is shown. (Any pause
intervals and the back-erase time if data back-erase is enabled are not included
in the measurement time.)
If data back-erase was enabled in step 9, the data are indicated on the display,
as shown below.

Manu
A Fast
80

10 20s
Data range to be excluded
59.1
Measurement screen

12. When the measurement is completed, you can use the Mode key to
switch between various ways of displaying the measurement result.
You can display the percentile sound levels selected in step 8, either
sequentially or simultaneously.

60
 Measurement

Note
It is also possible to use the Mode key during
measurement to read the percentile sound level up
to that point. (This applies only to the numeric level
display. The bar graph indication shows the sound
level.)
Changing the A/C/FLAT or Fast/Slow setting after
measurement is completed has no effect on the
displayed processing result.

61
Measurement

Back-Erase Function
When a measurement is being carried out and data are being processed, the
Pause/Cont key can be used to pause the measurement (i.e. to exclude data from
the point at which the key has been pressed), but it is also possible to exclude
(back-erase) data from an interval of 5 seconds before the key was pressed.
The data that are to be excluded are shown at the bottom of the measurement
screen.
Manu
A Fast
80

10 20s
Data range to be excluded
59.1
Measurement screen

To enable the back-erase function, proceed as follows.

1. Press the Menu key to display the menu screen 1/3.

<System> 1/3
Meas. time : 10min
Back Erase : Off Back-erase function
Cal mode : Internal
Manual data Clear : Off

Menu screen 1/3

2. Use the and keys to move the highlight to the “Back Erase: Off”
item.
3. Use the and keys to change the setting from “Off” to “5sec”.
Press the menu key to return to the measurement screen.
The indication “E” is shown on the display, indicating that the data
back-erase function has been enabled.

m Manu
E Shows that back-erase is ON.
20 80

Fast

Measurement screen
62
 Store Operations
The NL-20 incorporates a memory which can be used to store measurement
data (sound level, L eq and other processed values, measurement parameters
such as frequency weighting, time weighting, etc.).
This chapter describes how to store data in memory and how to recall data
from memory.

Storing Data in Memory

At the point where you press the Store key, the current sound level and all
processed values are saved. Immediately after turning the unit on, no pro-
cessing results exist. Therefore only the sound level gets stored.
The procedure for storing is as follows.
1. Turn the unit on.
2. Select the data number for the store process.
You can use the and keys to set the data number to a value
between 1 to 100.

Store key Mode key

Start Pause
Stop Store Mode Cont

A C FLAT Fast Slow

Menu Down Page Up Range

Recall Recall data Cal adj

Select Data number

Light Print Cal
with and keys
Power key
Power
NL-20
SOUND LEVEL METER

63
Store Operations

3. Press the Mode key and verify that no processing data exist for the
various items (all processing values are 00.0 dB).
If processing data exist, turn power to the unit off and then on again.
If stored measurement data exist, the earlier data will be overwritten
by the new data. For information on how to check for stored data,
please refer to the section “Reading Stored Data” on page 66.

Data number

Manu Manu

20 80 Leq : 00.0 L05 : 00.0

LE : 00.0 L10 : 00.0
Lmax : 00.0 L50 : 00.0
Fast
Lmin : 00.0 L90 : 00.0
L95 : 00.0
eq

Measurement screen List screen

Use the Mode key to switch between screens and
verify that all processing values are 00.0 dB

Important
Do not turn power to the unit off during the
store process. Otherwise internal data may be
damaged.

4. To store processed values, perform the measurement as described in

the preceding chapter (except for “Sound level Measurement”).

64
 Store Operations

5. Press the Store key.

The sound level at point when the key was pressed is stored.
The store process is completed in about one second, and the data
number is incremented by 1. Pressing the Store key repeatedly allows
you to consecutively store data.
The stored data comprise all information shown on the display (except
for the battery indication), as well as the current date and time, start
date and time of processing, measurement time, frequency weighting,
time weighting, and processing results.
The time/level graph shown on the display is not stored.

Important
The unit does not check whether data to be stored
are present. When the Store key is pressed, the
data in the currently selected data number are
overwritten, even if no new data are available.

Note
When the data number 100 is reached, the indication
does not change further and does not return to 1. When
the Store key is pressed in this condition, the “100”
indication flashes, but data are not stored. Pressing
the and (Data No.) keys to select another number
causes the indication to stop flashing, and data can
be stored in the selected data number.

65
Store Operations

Reading Stored Data

To read data stored, proceed as follows.
1. Turn the unit on.
2. Press the Recall key.
The recall screen appears.
3. Use the Recall Data and keys to select the data number in which
the data were stored. The data are shown on the display.
When there are no data in a number, the display only shows “--.-”.
Press the Mode key to switch between the stored sound level data
and the various processing results.

Important
When wishing to check whether data are present
in a data number, use the Mode key to switch the
display to sound level and then verify whether
data or “--.-” is shown on the display. If “--.-” is
shown in other mode settings, that data number
may still contain sound level data.

4. To terminate the recall mode, press the Recall key once more.

66
 Store Operations

Clearing Stored Data

To clear data stored in manual mode, proceed as follows.
1. Press the Menu key to call up the menu screen 1/3.
2. Set the “Manual data clear” item to “On”.
To clear (erase) the data, press the Start key. The manual data are
cleared, and the unit returns to menu screen 1/3 with the “Manual
data clear” item set to “Off”.

<System> 1/3
Meas. time : 10min
Back Erase : Off All data clear? All data clear?
Cal mode : Internal Switching display every 0.5 second
Manual data Clear : On
All data clear? Shown when "Manual Data
OK Start Cancel Pause Clear" is set to "On"
Menu screen 1/3

67
 Default Settings
The factory default settings of the unit are listed below.

Fast/Slow (time weighting) Fast

A/C/FLAT (frequency weighting) A
Level Range 30 to 120
Mode Lp
Meas. Time 10 min
Back Erase Off
LCD Contrast
I/O Baud Rate 19200 bps
Index 1
Output AC/DC AC
Light Auto Off 5 min
L eq On
L50 On
LE Off
L 05, L10, L90, L95 Off
L max, L min Off
LIST, T-L On

When you turn power to the unit on while holding down the Start/Stop key,
the unit will be initialized to the above settings.

68
 Output Connectors
AC Output
An AC signal corresponding to the frequency-weighted signal is output.

Output voltage: 1 Vrms ±50 mV rms (scale upper limit)

Output impedance: approx. 600 Ω
Load impedance: 10 kΩ or higher
Suitable cable: BNC-to-RCA cable CC-24 (option)

The relationship between unit reading and output voltage is as follows.

10

1
Output voltage (Vrms)

0.1

0.01

0.001

100

10

-90 -80 -70 -60 -50 -40 -30 -20 -10 FS +10

Scale (dB)
FS : Full-scale value

The output voltage when the unit is in calibration mode (-6 dB from scale
upper limit, 1000 Hz sinusoidal wave) is 0.5 Vrms.

To use the AC output, set the item “Output AC/DC” on menu screen 3/3 to
“AC”.

69
Output Connectors

DC Output
A level-converted DC signal generated by rms detection and logarithmic
compression is output. The signal reflects the frequency weighting and time
weighting settings of the unit.

Output voltage: 2.5 V ±25 mV (scale upper limit), 0.25 V / 10 dB

Output impedance: approx. 50 Ω
Load impedance: 10 kΩ or higher
Suitable cable: BNC-to-RCA cable CC-24 (option)

The relationship between unit reading and output voltage is as follows.

3.0

2.5
Output voltage (V)

2.0

1.5

1.0

0.5

0
-90 -80 -70 -60 -50 -40 -30 -20 -10 FS +10

Scale (dB)
FS : Full-scale value

The output voltage when the unit is in calibration mode (-6 dB from scale
upper limit) is 2.35 V.

To use the DC output, set the item “Output AC/DC” on menu screen 3/3 to
“DC”.

70
 Output Connectors

I/O Connector
This input/output connector serves for input of control signals and input/out-
put of measurement data.
The following types of cable can be connected.

- Printer cable CC-93

For data output to printer DPU-414, CP-10, CP-11
- Interface cable CC-92
For communication with a computer

71
 Optional Accessories
Microphone Extension Cables EC-04 Series
For measurements requiring special precision, the microphone can be removed
from the main unit and connected by means of an extension cable. This
reduces measurement deviations due to refraction effects and the acoustic
influence of the operator.

As shown in the table below, six types of cables with a length of 2 to 100
meters are optional. It is also possible to connect several cables in series.

Extension cable EC-04 series

Model Length Model Length

EC-04 2m EC-04C 30 m (reel) + 5 m (connection cable)
EC-04A 5m EC-04D 50 m (reel) + 5 m (connection cable)
EC-04B 10 m EC-04E 100 m (reel) + 5 m (connection cable)

Important
With long extension cables, the cable capaci-
tance restricts the upper measurement frequency
and measurement level. For details, please refer
to the Technical Notes.

72
 Optional Accessories

Printer DPU-414/CP-11/CP-10
Measurement data shown on the display, as well as data stored in the memory
of the unit can be printed out on a connected printer.
The procedure for printing is described below. Before starting, connect the
printer to the NL-20, turn both units on, and set the printer to the on-line
condition. Preparations as described in the chapter “Preparations” (page 9)
should also be completed.

Printing out measurement parameters

The contents of the display can be printed out.
1. Press the Menu key to call up the menu screen.
2. Use the Page Up/Down keys to select the page you want to print out
(1/3 to 3/3).

Start Pause
Stop Store Mode Cont

A C FLAT Fast Slow

Menu key
Menu Down Page Up Range
Recall Recall data Cal adj
Pressing the Menu key enables
the Page UP/Down key function
A C FLAT Fast Slow Light Print Cal
Power key
Down Page Up Power
NL-20
SOUND LEVEL METER
Print key

<System> 1/3
Meas. time : 10min
Back Erase : Off
Cal mode : Internal
Manual data Clear : Off

Menu screen example

Menu screen 1/3

73
Optional Accessories

3. Press the Print key.

Sample printout

Printing out data during a measurement (sound level display)

A hard copy of the screen is printed out.

m Manu

20 100

Fast

Sample printout

74
 Optional Accessories

Printing out data stored with manual mode in the internal memory
The following explanation assumes that data have been stored in the memory
of the unit.
To print out the data, proceed as follows.
1. Press the Recall key to call up the menu screen on the display.
2. Use the and (Data No.) keys to select the data for printout.
3. Press the Print key.
The printout contents will vary, depending on the contents (sound
level or processed values) shown on the display.

• When processed values are displayed

Example

m Manu
Recall indicator Data number

Fast

Recall screen example

4. To terminate the recall mode, press the Recall key again.

75
Optional Accessories

Level Recorder LR-06/LR-07/LR-04/LR-20A

For continuous recording of noise level changes, a level recorder can be con-
nected to the unit.

Sound level recording

The procedure for noise level recording on a level recorder is described below.
Before starting, connect the level recorder to the NL-20 and turn power on.
Preparations as described in the chapter “Preparations” (page 9) must also
be completed. For details regarding use of the level recorder, please refer to
its documentation.
1. Call up the menu screen 1/3 and verify that the “Cal Mode” item is
set to “Internal”. If “External” is shown, use the and keys to
move the cursor to “External” and use the and keys to set it to
“Internal”.

<System> 1/3
Meas. time : 10min
Back Erase : Off
Cal mode : Internal Cal mode
Manual data Clear : Off
set to Internal

Menu screen 1/3

2. Call up the menu screen 3/3 and set the “Output AC/DC” item to “AC”.

<I / O> 3/3

LCD Contrast :
Baud rate : 19200
Index : 1
Output AC/DC : AC Output AC/DC
Light Auto Off : 5min

Menu screen 3/3

When the setting is complete, press the Menu key to return to the
measurement screen.
3. Press the Cal key to set the unit to the calibration mode.
4. Activate the paper feed and pen operation of the level recorder to
start recording.

76
 Optional Accessories

5. Adjust the level control (Level adj) of the level recorder so that the
pen is at a point -6 dB below the full-scale point.

Recording pen

Recording range set to 50 dB

-6 dB point
Full-scale point
6. Press the Cal key once more to return to the measurement mode.
7. Use the A/C/FLAT key to set the frequency weighting. The time
weighting is adjusted at the level recorder.
8. Use the Level Range keys to select the level range. Choose a setting
in which the “Over” or “Under” indication does not appear.
The upper limit of the level range selected at the NL-20 becomes the
full-scale point of the level recorder.

Manu
E
20 Start 110 Full-scale point
Fast

Measurement screen

110 dB 100 dB 90 dB 80 dB 70 dB 60 dB

(Recording range set to 50 dB)

Full-scale point

77
 Specifications
Applicable standards
IEC 61672-1:2002 Class 2
JIS C 1509-1:2005 Class 2
IEC 60651 and IEC 60804 was withdrawn and replaced
by IEC 61672-1:2002.
JIS C 1502 was withdrawn and replaced by JIS C
1509-1.

Measurement functions
Main processing functions
Simultaneous measurement of all items according to selected time
weighting and frequency weighting
Sound level Lp
Equivalent continuous sound level L eq
Sound exposure level LE
Maximum sound level L max
Minimum sound level L min
Percentile sound level L N (5 selectable settings)

Measurement time
10 seconds, 1, 5, 10, 15, 30 minutes, 1, 8, 24 hours, and manual (maximum
200 hours)

Total range 28 to 138 dB

Max. measurement level

138 dB

Noise floor A weighting: 22 dB or less

C weighting: 27 dB or less
Flat: 32 dB or less

78
 Specifications

Linearity range 100 dB

Reference sound pressure level 94 dB
Reference level range 30 to 120 dB
Calibration check frequency 1 kHz
Level range selection
6 ranges in 10-dB steps 20 to 80 dB
20 to 90 dB
20 to 100 dB
20 to 110 dB
30 to 120 dB
40 to 130 dB
Frequency range
Overall characteristics including microphone: 20 to 8000 Hz
Electrical circuit characteristics (AC output): 10 to 20000 Hz
Electrical circuit characteristics (detector): 10 to 14000 Hz

Frequency weighting
A, C, FLAT

RMS detection Digital processor

Characteristics: Fast, Slow
Calibration
Electrical calibration with 1-kHz sinusoidal wave signal from built-in
oscillator
Calibration using sound calibrator

Back-erase function Pause key can be set to erase data from preceding 5
seconds
Processing functions
Digital processing
Sampling interval
30.3 μs (L eq, LE)
100 ms (L N)
Data store functions Data can be stored in the internal memory.
Max. 100 data sets for Lp, L eq, LE , L max, L min , L N can
be stored.
79
Specifications

Microphone
1/2-inch electret condenser type
Model: UC-52
Sensitivity: -33 dB

Preamplifier NH-21

Display
Backlit LCD (128 × 64 dots + 121 icons)
Display screens
Numeric and bar graph indication of sound level
Processing results screen
Level-time graph (real-time level recording with 20-
second horizontal axis)
Menu screens for operation settings
Warning indications
Over-range indication: full-scale +8.5 dB
Under-range indication: full-scale -2.6 dB

Outputs
AC/DC output
Key-selectable AC or DC output
AC output (using selected frequency weighting)
Output voltage: 1 Vrms (at full-scale)
Output impedance: 600 Ω
Load impedance: 10 kΩ or more
DC output
Output voltage: 2.5 V (at full-scale),
0.25 V/10 dB
Output impedance: 50 Ω
Load impedance: 10 kΩ or more

80
 Specifications

I/O connector Sound level meter control from and data output to a
computer
Data output to printer DPU-414 /CP-11/CP-10
Transfer principle
Transfer principle: asynchronous
Data word length: 8 bit
Stop bits: 1
Parity check: none
Baud rate: 4800, 9600, 19200 (bps)
Flow control: yes
Select X parameter control
or RTS/CTS control

Power requirements
Four IEC R6 (size “AA”) batteries
Battery life (23°C)
Approx. 34 h (alkaline batteries LR6),
Approx. 14 h (manganese batteries R6P)

With backlighting, battery life is reduced to about

half.
When auxiliary processing functions are enabled, bat-
tery life is reduced by about 20%.
When the optional filter is enabled, battery life is re-
duced by about 15%.

AC adapter (option)
NC-34: 100 V AC
NC-34A: 120 V AC
NC-34B: 220 V AC
NC-98A: 100 to 240 V AC (CE-marked)
NC-98B: 100 to 240 V AC (CE-marked)
Current rating (when 6 V DC is input)
Approx. 50 mA

81
Specifications

Ambient conditions
-10°C to +50°C, 10% to 90% RH (no condensation)

Dimensions
Approx. 260 × 76 × 33 mm

Weight (including batteries)

Approx. 400 g

Supplied accessories
Windscreen WS-10 1
Carrying case 1
Connector cover (mounted on unit) 1
Hand strap 1
Batteries IEC R6P 4
Product name label 1
Logo label 1
Inspection certificate 1
Instruction manuals 1 set
(Instruction Manual, Technical Notes, Serial Interface Manual, 1 each)

Optional equipment
AC adapter NC-34 series
AC adapter with CE mark NC-98A (100 to 240 V AC, 50 /60 Hz)
NC-98B (100 to 240 V AC, 50 /60 Hz)
BNC-to-RCA cable CC-24
Microphone extension cable EC-04 series
Serial I/O cable CC-92
Printer cable CC-93
Printer DPU-414
Sound calibrator NC-74
Pistonphone NC-72A
Level recorder LR-07/LR-20A

82
 Specifications

IEC60651 TYPE2 IEC60804 TYPE2

SOUND LEVEL METER

NH-21 NO.
MICROPHONE UC-52 NO.

260
MADE IN JAPAN
MODEL NL-20

JIS C 1502
SER.NO.

PREAMP

Start Pause
Stop Store Mode Cont

A C FLAT Fast Slow

Menu Down Page Up Range

Push

Open

Recall Recall data Cal adj

Light Print Cal

NL-20 Power

SOUND LEVEL METER

Rear View Side View Front View

33 76

AC DC I O
OUT

POWER

Bottom View

Unit: mm
Dimensional Drawings

83
No. 31675 08-05