Instrumentation and Control Engineering Department

B. Tech VII sem (Batch 2020-2024)

July-Dec 2023

Virtual Instrumentation
(ICPC-404)
VI lect_ notes #3 Course Coordinator
Data Acquistion fundamentals
NI-DAQ card , interfacing and LabVIEW Dr Roop Pahuja
Meas I/O functions Associate Professor
Data acq. and generation VI programs
Case studies Room No. 507
Virtual Instrumentation (ICPC-404)
Dr. Roop Pahuja
Contact No : 9988651877
1
 Data Acquisition ( DAQ)
DAQ : An Introduction
• Virtual instrumentation combines hardware and software with industry-
standard data acquisition and computing technologies to create user-
defined measurement/control solutions
• Data acquisition is one of the component of a real time VI system
followed by data analysis and presentation
• In a VI system, data acquisition hardware uses driver software compatible
with LabVIEW to perform real time measurements.
• National Instruments specializes in developing a PC-based general
purpose or specialized data acquisition hardware and driver software
compatible with LabVIEW to develop VI systems for real time monitoring
or control applications
• A general-purpose PC –based DAQ device acquires or generates different
types of signals on multiple channels for interfacing to real world devices
or systems signals.
• It is different from other measurement systems because the software
installed on the computer performs the actual measurements and
controls the DAQ system.
• The DAQ device converts the incoming signal into a digital signal and
format the same using communication protocols for computer interface.
Basic elements of data acquisition card
Vref and no. of bits selection

Pre-processed Anti-aliasing filter

signals
Analog /digital
on multiple
channels With S/H AI data
Communication interface

PC comm. port

To PC

LabVIEW application program

with driver layer functions are
used to read and write data
from multiple channels of DAQ
The equation to calculate the expected noise is as follows:

Absolute Accuracy = ±((Input Voltage * % of reading) + Offset + System

Noise + Temperature Drift
The resolution and device range of a measurement device determine the
smallest detectable change, called the code width, in the input signal. The
smaller your code width, the more accurate your measurements are.
You can calculate the code width using the following formula:

•code width = device range/ 2resolution

For example, a 12-bit measurement device with a 0 to 10 V range detects a 2.4
mV change, while the same device with a -10 to 10 V input range detects only a
change of 4.8 mV:
•device range/ 2resolution = 10/212 = 2.4 mV
•device range/ 2resolution = 20/212 = 4.8 mV

A high-resolution A/D converter (ADC) provides a smaller code width given the
preceding device voltage ranges.
•device range/ 2resolution = 10/216 = 0.15 mV
•device range/ 2resolution = 20/216 = 0.3 mV
DAQ Classification : Depends upon …
(i) General purpose or Specialized
signal measurement : analog/digital input –output analog and digital signals,
sound/ vibration, motion controller, image acquisition
(ii) Local or distributed (network- based)
Plug-in type
internal bus of a computer through a plug-in slot.
Portable ( serial, USB, parallel port)
External PC ports.
(iii) NI DAQ devices or third party DAQ devices (driver software
compatible with LabVIEW)
(iv) Based upon
Salient features/specification
--- Multifunctional: input and output signals types and number of channels
----- Plug-in/ portable
--- Suited for general purpose signals:
Classified depending the way it conveys info
Analog : DC, TD, FD
Digital : ON/OFF (TTL levels), Pulse train
----- No. of channels ( AI, AO, DI, DO) channels
------ Signal modes for analog inputs : Differential and single-ended
channels
DAQ : Signal types and uses
---- Signal ranges : ±10V; Multiple ranges (± 1V, ± 5V)
----- Sampling rate : max sampling rate for the device.
e.g.. 200kS/s
sampling rate per CH = Max sampling rate /number of used CHs
-- BW of DAQ (max freq. of input signal) = Max sampling rate/2.N
----- Resolution of ADC : no. of bits of ADC: 10bit, 12 bit, 16 bit
-- Code width : Min level of the signal measured
(Vref)

-- CH selector type : Screw terminal, BNC connector

---- Pin layout : Diagram specifying signals names
and CH with respect to pin no. on the channel selector: physical Ch to connect
signals
Example:-- NI-PCI 6221, NI-USB 6015, NI-USB 6009
• Salient features/specification
---- Code width : Min level of the signal measured

---- CH selector type : Screw terminal, BNC connector

---- Pin layout : Diagram specifying signals names
and CH with respect to pin no. on the channel selector: physical Ch
to connect signals
E.g :-- NI-PCI 6221, NI-USB 6015, NI-USB 6009
Code width : provides relationship between signal range, PGA, ADC ref

In order to digitize an input signal with best of the resolution of DAQ device, it is required to select the
device range (Vin_range) to match the input voltage range. By selecting the device range, the gain of
PGA (G) is set automatically to match the input voltage range to the Vref for ADC as given by the
equation:
Vin_range x G = Vref for ADC
Given a DAQ device:
Vref for ADC is fixed = 5V (unipolar or bipolar)
For analog input signal measurement:

Vin range is selected by the user during configuration of DAQ so that unknown signal is within the
range selected. Then driver software sets value of G for PGA so that the selectable device range
should best match the Vref for ADC

The code width with which the unknown voltage is digitized is given by:
code_ width = Vref/(G. 2n )
= device range /2n
where, device range = Vref/(G)
Q. 1 A typical DAQ uses 10bit ADC with ref of ±5V with bipolar/unipolar selection. The
PGA has gain setting of 0.5, 1, 2, 5,10.

The DAQ software provides the user with selectable unipolar and bipolar signal ranges of
0-10V, 0 to 5V, 0 to 2V, -5 to 5V.
If the system is used to measure the signal that varies in the range 0 to 2 V, find the
appropriate selectable signal range and gain setting of PGA. Also find the code width of
the signal.

Ans : Input voltage range = 0-2V

User selectable device range for DAQ = 0-2V ( best match)

Automatic PGA gain setting G = Vref/ device range = 2.5

selected gain setting = 2 (best match)

Code width = Vref / G 210 = 5 / 2 x 2 10 = 0.0024 V

Q.2 A typical NI DAQ system uses PGA with gain setting of 0.5, 1, 2, 5, 10
and 10-bit ADC with ref voltage of ± 5V. Suggest the available signal ranges
specified by DAQ.
Also find the resolution with which voltage signal in the range 0-1V is digitized signal
if Vref is 5V.

Signal ranges = ADC ref/G

Available signal ranges on DAQ : ± 10V, ± 5V, ± 2.5V, ± 1V, ± 0.5V

Code width = 5V/5. 1024) = 0.9mV

 DAQ In LabVIEW
Different Hardware

NI DAQ Devices Third party devices

General –Purpose General –Purpose
specialized specialized
(Local/portable/network based/ wireless connectivity/embedded hardware )

Driver software ( available in function palette) Requirement of LabVIEW

MAX : utility software available compatible Driver software
LabVIEW compatible driver software is in-build Driver software interacts with
VISA (Virtual Instrument Software
Architecture) functions

VISA is Standardized software interface to communicate with DAQ hardware using any communication protocol.
Procedure for PC –based data acquisition/measurement in LabVIEW
Shows the procedure of data acquisition to measure real world signals using DAQ device and LabVIEW
software: Use of NI DAQ hardware + MAX (utility software) + Driver software + LabVIEW application
software to acquire/generate data in LabVIEW to interact with real world phenomenon.
Steps for data acquisition in LabVIEW using NI DAQ hardware

• Use a suitable DAQ and connect to PC USB port

• Go to MAX (utility software) for detection and testing of Device
• In MAX device is detected under Devices and interfaces. See Pin out of the
device , Rgt. click on detected device , Go To  Pinouts
• Interface sensor and actuators to suitable CHs of DAQ
• Make VI program for data acq. of signals using DAQ Assistant (express VI
function in Meas I/O sub palette ) by configuring the channels used.
• Process the signals , write control algo and initiating CS (analog /digital to
port CHs of DAQ)
• Make a VI program for display of data on UI
What is MAX: Measurement and Automation Explorer
 It is an Utility software for data acquisition in LabVIEW
Provides access to your National Instruments hardware devices including
variety of data acquisition cards or modules
Helps to detect the devices and instruments connected to PC system.
Helps to execute system diagnostics and run test panels.
Provides the pin details of the channel selector of data acquisition card
connected to PC for interfacing of signals
Steps to Use MAX : To detect and test DAQ
• Connect NI-DAQ to PC.
• Open MAX ( LabVIEW  Tools  MAX)
• Check detection of DAQ in MAX : If the device is connected to PC and is
detected by MAX it is indicated under DAQmx devices
MAX My system  Devices -> DAQmx
Devices -> DAQ 6009/ DAQ 6015

• To test CH : Go to ‘Test panel’ tab and test the signals connected to CH

• To see pin outs : Rgt. click on DAQ  pin outs
NI- 6009 DAQ card is connected to USB port of
PC

A window indicating the card pops –up to select

LabVIEW to build a program.

Open LabVIEW
Go to Tool menu
select MAX to detect and test the device
Open MAX : LabVIEW  Tools  MAX
Using MAX : To detect DAQ (6015)
• Pin configuration of typical DAQ (6015)
If the card is not detected then x is indicated
 DATA ACQUISITION IN LabVIEW
using
General purpose NI DAQ devices
(NI 6015 (USB); NI 6009 (USB); NI 6221 (PCI))
and DAQ Assistant
NI-DAQ 6015
Important specifications
 Analog CHs : 16 SE ( signal line +S and Agnd),
 8 differential ( + S, -S, Agnd)
 Analog output : 2 CHs
 Digital I/O ports : 2 ports , 16 lines ( I/P or O/P).
 Max signal range =  10V, (other selectable ranges) 0-10,  0-5V, 0-5V, 0-1V,
 PGA with different gain settings (0.5 , 1, 2, 5, 10 ), unipolar /bipolar
 ADC Vref =  5V,
 Sampling rate = 200KS/s
 Multifunctional USB based
 Analog Inputs Use AI 0 and AI Gnd for SE connection
Digital lines at port
Use AI 0 (+)and AI 8 (-) with Agnd for diff
connection on CH AI 0

Analog outputs
Onboard exc
DAQ device Pin Nos. and Signal names: Pin configuration table represents pin no. and associated signal name
representing signal type and CH no.

Signal name Pin No. Description

AI 0 1 Analog input signal at CH0 to15 and gnd
AI 1 4 Single ended connection uses: Ch (AI0 to
…. … AI15) and gnd
AI 15 27 Diff uses : + ch and-ch (+ive Chs are AI0
AI GND 3,6,9… to AI7) ; neg Chs (AI8 to AI15)

AO 0 15 Analog output signal at CH0 and1 and

AO 1 31 asso. Gnd
AO GND 16, 32

P0.0 33 Digital signal port 0 line 0

…. …. ….
P0.7 42 Digital signal port 0 line 7
(digital lines used as i/p or o/p)

D.Gnd 35,39, 43 Digital gnd

NI-DAQ 6009
Important specifications
 Analog CHs : 8 SE ( signal line +S and Agnd),
 4 differential ( + S, -S, Agnd)
 Analog output : 2 CHs, 0-5V, 5mA current drive
 Digital I/O ports : 1 ports ( 8 lines) , 2 port (4 lines) (software selectable I/P or
O/P).
 Max signal range =  10V, (SE) (other selectable ranges)
 diff : ±20 V , ±10 V, ±5 V, ±4 V, ±2.5 V, ±2 V, ±1.25 V, ±1 VADC
Vref =  10V,
 Sampling rate = 48KS/s
 Input impedance = 144 kΩ
 Overvoltage protection= ±35 V
 Multifunctional USB based
 Channel connection type : screw terminal type
AI : analog input
AI 0-AI 8: SE
+- AI 0 to +- AI 4: Diff

AO : Analog o/p
AO 0 to AO 1

P0.0 –P0.7 : Digital port 0

to lines 0-7

Exc : 5V , 2.5 V
 Study of driver layer functions for data acquisition in LabVIEW
(a) DAQ Assistant (express VI) Fn. Palette  Meas I/O  DAQmx  DAQ Assistant
Is a driver layer function available as an express VI that allows one to configure the connected DAQ device to read or write
signals from specified channel/s. Common configuration parameters are: DAQ device no., signal type (analog or digital),
mode (data read or write) , CH no. (one or add multiple channels), voltage range, timing parameters.

DAQ Assistant configuration modes

DAQ Assistant DATA terminal

Data terminal: Dynamic data type –read or write

analog or digital data from/to CHs

Data terminal is at the output to read analog

inputs (AI) or digital inputs (DI) for acquiring
signals: DAQ is configured in read mode

Data terminal is at the input to write analog

output or digital output signals to CHs for
actuation: DAQ is configured in write mode
(b) Convert from dynamic data ( express VI signal manipulation  To DDT)

Converts the dynamic data to numeric or Boolean scalar/array data types for use with other VIs

(c) Convert to dynamic data. ( express VI signal manipulation  To DDT)

Converts the numeric , Boolean data to dynamic data types for use with express VI for data
acquisition DAQ
DAQ VI programs : Reading and writing signals to different CH of DAQ

(a) Analog Input : Make a VI program to continuously read analog

voltage from AI0 CH of DAQ 6015
(i) Physical connecting signal to designated CH - AI0 (Single-ended)

V Power
supply
+ -

Analog voltage
(ii) To make a VI : Place DAQ Assistant on BD and configure it
 Select Device : Daq 6015 (dev1)
 Select acq mode : Acquire or generation
signal type : Analog input
 Select Ch no. : AI 0
Select CH mode : RSE,
Voltage range : ± 10V
 Select sample mode : Sample on demand
Click OK….. Wait …… DAQ Ass builds…. Data
Terminal is available
(iii) Complete VI program with while loop, voltage
indicator and a waveform chart

Configured for AI0

 (iV) Run program and read voltage value as acquired from
the designated CH on panel
(iv) Actual physical system displaying value
 (b) Analog output : Make a VI program that writes analog
voltage (0 to10)connected to AO0 CH of DAQ
(i) Physical connecting signal to designated CH : DAQ card
interfacing

Voltage
Indicating
meter
- +
 (ii) To make a VI : Place DAQ Assistant on BD and configure
it
 Select Device : DAQ 6015 (dev1)
Select acq mode : Generation
 Select signal type : Analog output
 Select Ch no. : A0 0
 Voltage range : 0 to 10V
 Select sample mode : Sample on demand
Click OK….. Wait …… DAQ Ass builds…. Data
Terminal is available
(iii) Complete VI program :
Generate analog output voltage at output

Convert numeric scalar to dynamic data type

 (c) Digital O/p : Make a VI program that writes digital signal
(T/F) to ON/OFF LED connected to digital line P0.0
(i) Physical connecting signal to designated CH

+ 250ohm

LED is connected to PO0 digital line

 (ii) To make a VI : Place DAQ Assistant on BD and configure
it
 Select Device : Daq 6015 (dev1)
Select acq mode : Generation
 Select signal type : Digital
Select Line no. : P0.0
 Mode : Output
 Invert : no (check box not clicked)
 Select sample mode : Sample on demand
Click OK….. Wait …… DAQ Ass builds…. Data
Terminal is available
 Use On/OFF switch to write Boolean data to o/p digital line
connected to LED.
Convert Boolean data to array to data terminal input
of DAQ Assisstant
 (iii) Complete VI program . Use On/OFF switch to write
Boolean data to o/p digital line. Feed array to Boolean array
to data terminal input.
 (iii) Complete VI program . Use On/OFF switch to write
Boolean data to o/p digital line. Feed array to Boolean array
to data terminal input.
 (d) Digital I/P :Make a VI program that reads digital signal
(T/F) connected to digital line P0.1
(i) Digital input signal to designated CH

Mechanical switch

5V

Digital signal input to P0.1

(ii)To make a VI : Place DAQ Assistant on BD and configure it
 Select Device : Daq 6015 (dev1)
Select acq mode : Acquisition
 Select signal type : Digital
Select Line no. : P0.1
 Mode : INPUT
 Invert : no (check box not clicked)
 Select sample mode : Sample on demand
Click OK….. Wait …… DAQ Ass builds…. Data
Terminal is available
Read the status of the switch connected to DAQ PO.1
When switch is OPEN (OFF state)

When switch is closed

Index array
 DAQ program with mixed- multiple signals :
Eg. Read Analog, Read Digital signal , write analog, write
digital

• To read mixed signals from DAQ, Use DAQ Assistant for each signal type .
ADD Chs if multiple signals of same signal type are required.
• If the operation is not providing sequencing in in the use of DAQ Assistants
for different signals types then use of Sequence structure for different
DAQ Assisstant (example reading AI and DI) , otherwise don’t use
sequence. ( AI and DO)
 (e) Make a VI program that reads multiple analog inputs from
different channels.
 Read multiple Chs of same signal type from DAQ
 Use ADD CH to configure DAQ for acquisition of signals on multiple channels .
 Configure DAQ for one CH and then ADD channels with same configuration
parameters
Place DAQ Assistant on BD and configure it for one analog input channel and then add another
ch (DAQ ASSISSTANT CONFIGURATION)

 Select Device : Daq 6015 (dev1)

Select acq mode : Acquisition
 Select signal type : Analog input
 Select Ch no. : AI 0
Select CH mode : Differential ( only mode available)
 Voltage range : ± 10V
 Select sample mode : Sample on demand
Click OK….. Wait …… DAQ Ass builds…. Data
Terminal is available

Then go to < ADD channel> tab and select another channel .. Ai1 etc ---- , click OK
Use AI0 and AI2 Chs reading SE signal but configured as diff

+
V1

+
V2

I/P voltage Circuit diagram showing interfacing of Multiple analog input

signals to DAQ
sources
 Ch AI0
Ch AI2

Dynamic data containing voltage

samples of two channels in an Convert dynamic data to array
array indexed in sequence of Array elements contain voltage samples of the CH used
channels configured
Example Program : Mixed signals Acquisition (AI and DO)

Make a VI program that reads SE analog voltage signal from channel AI0 of DAQ NI-
6009 . If the signal value exceeds the alarm limit of 6V, LED alarm connected to
DAQ channel P0.1 is activated. Show the physical connection diagram and DAQ
configuration

Analog Read Digital write

Place DAQ assistant and configure for AI0 RSE
 Error condition in the use of DAQ Assistant
• DAQ Assistant : when DAQ Assistant are accessed simultaneously without sequencing,
then error is generated
• To use DAQ Assistant for accessing the signals simultaneously, it is recommended to
use SEQUENCE structure. In each frame od DAQ Assistant place DAQ Assistant to
access CHs in a sequence
• Sequence structure
In as sequence structure there
are different frames and code
executes in a sequential
manner.

The output from each frame is

available to other frames or
outside the frame.

Data from outside can be taken

to each frame through tunnel
at the border

Zto use sequence structure

with DAQ Assisstant,
Each frame has a DAQ Assistant
configured to read/write
analog/ digital signal and data
from one frame flows to
another depending upon the
program code.
Use DAQ assistant in each frame
Q.1 Make a VI program to generate random voltage in the range 0-10V
at output channel AO0 after 5s of time interval until STOP button is
pressed. Also read the generated voltage at CH AIO and display on a
chart.

Q.2 Make a VI program to read voltage from analog input channel AI0,
AI1, AI2 after 5s of time interval until STOP button is pressed and
display time- variations of voltages on a chart. Also log the voltage
samples in a file.
• CASE Study 1: PC based VI system for
Temperature Monitoring and
Logging
Problem 1
Make a VI program to continuously monitor room temperature until STOP button is
pressed using LM35 smart temperature transducer. Interface the temp sensor with NI-
6015 DAQ card and draw the interfacing diagram.
Display the temperature variations on chart and log the readings

System hardware/software : standard PC, DAQ NI 6015

LM35 IC temperature sensor (3 terminal (gnd, Ex, o/p) 10mV/°C, -40 to 120°C) ,
LabVIEW 2015 or higher PDS
Interfacing LM 35 to NI DAQ card using external power source

AI0 CH is configured in Differential mode but used as SE

Excitation signal of 5V is given to sensor from external PS unit
Output voltage of sensor is interfaced to DAQ ch AI0 (selected as diff)
Alog :
Use while loop with STOP button
Set Time increment = 1s
Configure DAQ assiatnt with foll parameters
……………………..
…………………,,,,,
………………….
At iteration i = 0
Read analog voltage at AI0 from DAQ Assistant
Convert dynamic voltage to scalar voltage using FROM DDT function
Convert voltage sample (V) to temperature sample (C) using
Ti = Vi X 100
Display temperature on indicator
Link temperature to chart for graphic display
If STOP= T
Abort VI
otherwise i= i+1
Repeat Process and continuously show data on front panel.
 Program to monitor temperature using LM35 sensor
Conversion of sensor voltage to engineering unit in C
Vs = 10mV/C x T ( static transfer function of the sensor)
T = Vs x1000 mV / 10 C
Or T = Vs X 100 C or Vs/0.01

Sensor voltage at Ch AI0

Eq to conv sensor voltage to temp

Set up to measure ambient temp of LAB using LM35 sensor and vary temp by heating the
sensor

Physical Interface of LM 35 sensor with DAQ .

Problem 2 : Temperature monitoring, logging and display of logged data on a table
Problem 3 : Temp sensor powered by DAQ
Make a VI program to continuously monitor temperature of a room using LM35
sensor after 1s of time interval until STOP button is pressed. Use DAQ 6015.
Provide 5V excitation signal to sensor from DAQ channel AO0.
Display temperature variation on a chart and log relative time -temp data in a file.
Also compare temp value with high and low alarm status and display low and high
alarm status.

Procedure:
 Do physical interfacing : Provide excitation of 5V to sensor from
DAQ AO0 and connect sensor output to analog input channel AI2
 Make VI program
 Use three frame sequence structure VI :
Seq structure : Frame 1 : Configure DAQ Asst. to write analog
voltage value of 5V to AO0
Seq structure : Frame 2 : Use wait fn with 20ms wait time to
stabilize excitation signal for sensor to take reading.
• Seq structure : Frame 3 : Configure DAQ Asst. to read sensor
voltage signal at ch AI0
 Convert sensor voltage to Temp in C using S value of 10mV/C.
 Display temp
 log time-temp data in file,
 Analyse temp value for to activate alarms .
 Display alarms
For continuous monitoring use outer while loop with time interval of 1s
and Stop button
Interfacing LM 35 to NI DAQ card using excitation signal from DAQ

Excitation signal of 5V is given

to sensor from DAQ AO0
Output voltage of sensor is
interfaced to DAQ ch AI0
(selected as diff)

AI0
AI0
AI8
Agnd

+5 V AO0
AO gnd
Gnd
DAQ 6015
Exc from DAQ A0 0

Read sensor voltage

AI1
Time -Temp logging in file
• CASE Study 2: PC based VI system for temperature Monitoring and
Control using ON-OFF dead-band controller

Interfacing Diagram : Temp sensor and actuator with DAQ card

ON-OFF Dead band control algo for temp control using heater

If Ti > TSLH (temp is greater than set limit high)

CSi = FALSE (Controller O/P is FALSE (DO))  Relay is deactivated  Heater (Hi)  OFF
state
Else If Ti < TSLL (temp is less than set limit high)
CSi = TRUE (Controller O/P is TRUE (DO))  Relay is activated  Heater (Hi)  ON
state
Otherwise CSi = Csi-1 (Controller O/P is at the prev state) 
Hi = Hi-1 (heater remains at the prev state)
Where Ti presents value of temperature at current ith iteration
Hi presents status of heater at current ith iteration
Hi-1 presents status of heater at i-1 iteration, CSi and CSi-1 , control signal at the ith and (i-1)th iteration
VI program for Temperature monitoring and control
Case Study 3: Use of filtering concepts in real-time acquisition of low freq temperature signals
Problem 1 : Continuous acquisition of senor voltage and averaging to improve noise
immunity
Problem 2: Make a VI program to monitor temperature using LM35 sensor interfaced to NI
DAQ card. Use 6-point moving averaging filter to acquire and filter the voltage and
temperature signal