DIFFERENTIAL PRESSURE SWITCHES

! GOOD REPEATABILITY

301 / 303 / 304

381 / 384

! HIGH STATIC PRESSURE !

! TAMPERPROOF SET POINT ADJUSTER WITH LOCKING DEVICE !

! WEATHERPROOF OR FLAMEPROOF HOUSING !
! OVERTRAVEL STOP ! RUGGED DESIGN !

STYLE 301 IN GK ENCLOSURE

Series 300 Pressure Difference Switches are designed

and made to the latest standards to comply with current
international philosophy of process instrumentation. The
series is compact , easy to install and features high sensitivity
over the fully adjustable range together with very high

STYLE 301 IN GM ENCLOSURE

static pressure capability. The sensing element is mounted

external to the switch mechanisms which are of stainless
steel for ardous atmospheres and high humidity. Enclosures,
sensing element and switching modes can be combined
to offer the variety needed to suit the different applications.

GENERAL SPECIFICATIONS
Enclosure
GM
GA
GK

Ranges

Switching Differential
Pressure die cast Aluminium,
weatherproof to IP:66

Fixed or Wide band adjustable,

refer table.

Max. Working Pressure

316 SS, investment cast, weatherproof to IP:66

110 bar for 301, 303 & 381

250 bar for 304 & 384

Ambient Temperature

()25C to (+)60C

Max. Process Temp.

70C. For higher temperatures use

longer impulse lines. (Note 15)
Ask for piping nomogram #441184-4

Die cast Aluminium, weatherproof

to IP:66 & flameproof to Gr.IIA, IIB
or IIC for H2 GAS (Note 1)
Several standard ranges between
3 mbar to 15 bar

Connection
Process

" NPTF. Adaptors for other sizes

optional

Electrical

" ET (F) std. " NPTF optional.

For Gr.IIC " NPTF alone is
available. Dual entry on request.

Sensor

316L SS Diaphragm

Wetted parts

304 SS or 316 SS

Repeatability

1% FSR (Note 4)

Scale Accuracy

5% FSR (Note 6)

Mounting

Switching Element

Instrument quality SPCO(SPDT)

microswitch (Notes 10 & 11)

Back panel/wall/Field.
position only

Conformity

Generally to BS 6134:1981

Vertical

QS Accreditation
R030

ORDERING MATRIX
!

ENCLOSURE
Pressure Die Cast Aluminium
weatherproof to IP:66 with Nitrile
gasket.

GM

Investment cast 316 SS weatherproof to IP:66 with overall size as

style GM fit for offshore.

GA

Die Cast Aluminium flameproof

cum weatherproof. CMRI approved
to Gr.IIA, IIB of IS:2148: 1981 for
flameproofness & IP:66 for weatherproofness. For Gr.IIC same
enclosure with specific certification
at extra cost is available.

RANGE CODE & AVAILABILITY

!

RANGE
CODE

RANGE

301/
304

303

381 /
384

C 6D

3 to 25 mbar

"

"

E 1D

5 to 120 mbar

"

"

"

E 8D

50 to 350 mbar

"

"

"

G5B

0.1 to 1.5 bar

"

"

"

J0 B

0.2 to 4 bar

"

"

M2B

0.7 to 7 bar

"

"

P 8B

1.5 to 15 bar

"

"

GK

MODEL
This is the basic differential pressure
switch having close fixed non-adjustable
switching differential actuated by a
stainless steel diaphragm.

301

Same as 301 but with auxiliary mechanism

permitting switching differential adjustment
over a wide band.

303

Same as 301 but suitable for higher static

pressures upto 250 bar.

304

A variant of series 300, employs twin

levers each operating a SPCO
microswitch actuated by a single sensor
through a unique linkage thereby providing
two independent adjustable set points,
each with its own setting scale, spring
and switch.
Same as 381 but suitable for higher static
pressures upto 250 bar.

SWITCH CODE RATING & AVAILABILITY

!

SWITCH
CODE
(SPCO)

381

384

MATERIALS OF WETTED PARTS

3
3
!

316L SS diaphragm with 304 SS pressure chambers.

02

316L SS diaphragm with 316 SS pressure chambers.

06

Conforming to NACE Std. MR-01-75.

0N

!
!

4
5
6

Nitrile diaphragm with 304 SS pressure chambers

for applications with pressure reversal.

R2

Nitrile diaphragm with 316 SS pressure chambers

for applications with pressure reversal.

R6

8
9

DIAPHRAGM CHEMICAL SEALS

Diaphragm chemical seals can be provided as optional extra
with capillary and threaded / flanged connection, duly evacuated
and filled with suitable filling liquid. This device permits the
use of differential pressure switches with viscous / aggressive
fluids and permits higher process temperatures.
While ordering it is important to specify ambient and process
temperatures, setpoint, maximum process pressure, relative
elevation between connection and switch head, nature of process
medium and whether reactive to common filling liquids should
the diaphragm seal leak into the process. However, switching
lag will be experienced unless the pressure change is very gradual.

G
E
F

DC RATING IN AMPS
AVAIL ABIL ITY AVAIL ABIL ITY
RESISTIVE
INDUCTIVE
OF SPCO IN OF DPCO IN
MODEL S
MODEL S
220V 110V 24V 220V 110V 24V
15A 250 /
301, 304,
0.2 0.4 2.0 0.02 0.03 1.0
301 & 304
125V
381 & 384
301, 304,
15A 250 /
N.R. N.R. N.R. N.R. N.R. N.R.
301 & 304
381 & 384
125V
15A 250 /
0.3 0.5 10.0 0.3 0.25 6.0
303
303
125V
301, 304,
301 & 304
1A 125V N.A. 0.5 0.5 N.A. 0.25 0.25
381 & 384
5A 250 /
0.2 0.4 5.0 0.2 0.4 4.0
301 & 304 301, 303 & 304
125V
301, 304,
301 & 304
0.1A 125V N.A. N.R. 0.1 N.R. N.R. N.A.
381 & 384
AC
AC
RATING

N.R.
5A 250 /
125V
4A 115V
400 Hz.
N.R.
15A 250 /
125V
15A 250 /
125V

N.R. N.R. 1.0 N.R. N.R. 0.5

301 & 304

301 & 304

N.A. N.A. 5.0 N.A. N.A. 3.0

301 & 304

301 & 304

N.A. N.A. 3.0 N.A. N.A. 1.0

301 & 304

301 & 304

N.R. N.R. 1.0 N.R. N.R. 0.25

301 & 304

301 & 304

0.30 0.75 15.0 0.2 0.4 10.0

301 & 304

---

0.30 0.75 15.0 0.2 0.4 10.0

301 & 304

---

Codes 3 & D For General purpose usages.

Code 4 With Noble metal contact.
Codes 5 For General purpose with good DC rating.
Codes 6 With Noble metal contact (Low Rating)
Code 7 Environmentally sealed switch with Gold
plated contact.
Code 8 Environmentally sealed switch with Silver
alloy contact.

Code 9 Hermetically sealed, inert gas filled with

Silver alloy contact.
Code G Hermetically sealed, inert gas filled with
Gold plated contact.
Codes E & F Manual reset switch. Auto change
over on rising and falling pressure respectively.
Resetting is Manual.

For DPCO, change switch code 3 to 33, 4 to 44, etc., while ordering
N.A. Not Available

N.R. Not Recommended

NOTES
11. Contact life of microswitches are 5 105 switching cycles for nominal load.
To quench DC sparks, use diode in parallel with inductance, ensuring polarity.
A RC network is also recommended with R value in Ohms equal to coil
resistance and C value in micro Farads equal to holding current in Amps.

1. Gr.IIA & IIB of IS:2148 is equivalent to NEC CL.1, Gr.C & D. Gr.IIC of
IS:2148 is equivalent to NEC CL.1, DIV.1, Gr.A & B.
2. Style GM/GA is weatherproof only if all entries and joint faces are properly
sealed. Style GK is weatherproof only if cover O ring is retained in
position and proper cable gland (flameproof) is used. It is recommended
to procure cable glands along with GK instruments to avoid neglect of it
during installation.

12. Model 301 can be supplied with Nitrile diaphragm for applications where
pressure reversal is envisaged.
13. All differential pressure switches are calibrated by applying pressure to HI
port, venting LO port to atmosphere. Inspection will also be limited to such
a practice.
14. Ambient temperature range: All models are suitable for operating within a
range of ambient temperature from () 25C to (+) 60C provided the process
does not freeze within this range. Below 0C, precautions should be taken
in humid atmospheres to prevent frost formation inside the instrument from
jamming the mechanism. Occasional excursions beyond this range are
possible but accuracy might be impaired. The microswitch is the limiting
factor which should never exceed the limits () 50C to (+) 80C.
15. Fluid Temperature: A Differential Pressure switch connected to the main
pipe is not subjected to the flow and therefore is not fully exposed to the
fluid temperature. Use of adequate length of impulse piping will greatly
reduce excessive heating of the sensing element. For example connection
of 7.5 cm of 12 mm dia impulse piping will reduce water temperature of
100C to 65C at an ambient temperature of 50C. Ask factory for temperature
nomogram for different temperatures.

3. Intrinsic Safety (Exi) Pressure Switches are classified as simple electrical

apparatus as per BS 53456.3.3. Hence Pressure Switches with GM/GA
enclosures may be used in intrinsically safe systems without certification if
energy levels are limited to 1.2V, 0.1A or 25 mW.
4. Accuracy & Repeatability are one and the same for all blind differential
pressure switches. A shift of 2% may be observed in setpoint when
pressure falls from full static pressure. Settings will also shift with varying
temperature.
5. The instrument is calibrated in the mounting position depicted in the drawing.
Hence mounting in any other direction will cause a minor range shift, especially in
low and compound ranges. Ranges above 1 bar will not experience this shift.
6. A Differential Pressure switch is a switching device and not a measuring
instrument eventhough it has a scale with 5% FSR accuracy to assist
setting. For this reason, Test Certificates will not contain individual ON-OFF
switching values at different scale readings. Maximum differential obtained
alone will be declared, besides other specifications.

16. Ensure that impulse pipework applies no stress on sensing element housing
and use spanners to hold pressure port / housing when connections are made.
17. Custom built instruments are available for special service requirements under
Special Engineering Category.
18. For less rigorous applications models 306 / 386 with Nitrile diaphragm &
Aluminium wetted parts are available at lesser cost.

7. Select working range of the instrument such that the set value lies in the mid
35% of the range i.e., between 35% and 70% of range span.
8. For switching differential values please refer respective Range Table. Switching
differentials furnished are nominal values under test conditions at mid-scale
and will vary with range settings and operating conditions.
9. On and off settings should not exceed the upper or lower range span.

19. Complementary instrumentation for pressure is available in 200 series.

20. Accuracy figures are exclusive of test equipment tolerance on the
claimed values.
21. All performance data guaranteed 5%.

10. DPCO action is achieved by two SPCO switches synchronised to practical

limits i.e., 2% of FSR. Deadband for DPCO contacts are higher than that
of SPCO as force required to actuate the contacts are more. Please refer
respective range table.

SWITCHING DIFFERENTIAL DATA

TABLE : A GM / GA Enclosures
On-off differential values for DPCO switching,
DPCO (2 SPDT)

On -o f f Dif f er en t ial in m b ar
R an g e
Co d e

F i x ed
R an g e

Mo d els 301 / 304

D/3/6

C 6D
E 1D
E 8D
G5B
J0 B
M2B
P 8B

3 to 25 mbar
5 to 120 mbar
50 to 350 mbar
0.1 to 1.5 bar
0.2 to 4 bar
0.7 to 7 bar
1.5 to 15 bar

6
5
12
60
175
300
800

A d j u s t ab l e
Mo d el
381/4

7 / 8 9 / G D/3/4/6

6
6
12
10
6
10
20
12
15
20
40
30
60
85 125 120
200 400 450 500
350 1200 800 900
800 1800 --- 1600

7.5
20
40
250
400
600
---

! For style GM/GA enclosures apply a multiplication factor

of 1.3 to values in TableA.

Mo d el 303
5

8 to 20
--13 to 70
40 to 70
26 to 200 50 to 200
111 to 900 250 to 900
-------------

On -o f f Dif f er en t ial in m b ar
F i x ed
R an g e

Mo d els 301 / 304

D/3/6

C 6D
E 1D
E 8D
G5B
J0 B
M2B
P 8B

3 to 25 mbar
10
5 to 120 mbar
8
50 to 350 mbar
20
0.1 to 1.5 bar
100
0.2 to 4 bar
300
0.7 to 7 bar
500
1.5 to 15 bar
1350

! In case of adjustable on-off differential models the

multiplication factor is to be applied only to the lower
limit of the differential values. Upper limit values remain
unchanged.
! For range codes M2B & P8B in models 301, 304 DPCO
switching using switch codes 3, D & 4 only is possible.

TABLE : B GK Enclosure

R an g e
Co d e

! For style GK enclosure apply a multiplication factor of

1.2 to values in TableB.

4
10
10
25
100
340
600
1350

Special Engineering : Higher DP range of 10 to 60 bar,

model 301 DP switch is offered with 316L SS bellows
sensor. But the out of balance pressure will be limited to
80 bar. For details refer offer/factory.

A d j u s t ab l e
Mo d el
381/4

7 / 8 9 / G D/3/4/6

10
20
17
12
16
34
20
30
40
70
50
55
140 210 200
350
600 765 900
600
2000 1550 1350 1000
2200 --- 2700
---

Mo d el 303
5

13 to 25
--21 to 70
35 to 70
52 to 200 80 to 200
182 to 900 425 to 900
-------------

! Switching differentials for Instruments with chemical

seal : Apply a Multiplication factor of 1.3 for SPCO and
1.5 for DPCO to values given in table for GM housings
and apply a multiplication factor of 1.2 for SPCO and
1.5 for DPCO to values of table for GK housings.
Chemical seals are not available in ranges C6D,
E1D & E8D.

OPTIONS / ACCESSORIES
!
!
!

Damping coil for minimising process pulsations increases

instruments life many times.
Breather / Drain for flameproof enclosures; blow out disc for
weatherproof enclosure.
Snubbers

!
!
!

Brass / SS double compression cable glands to suit cable OD

of 1/2", 15 mm & 17 mm.
Degreasing for Oxygen service & special parts for Ammonia
service.
Provision of line fault monitoring.

OVERALL AND MOUNTING DIMENSIONS

GM / GA Enclosure
2" Pipe Mounting Details

Range Codes : E1D, E8D, G5B, J0B, M2B & P8B

Surface / Wall Mounting

Fixing on
Vertical Pipe

Pipe Mounting

Fixing on
Horizontal Pipe

! Use 2 3/8" 25 long screws

and nuts for surface mounting

or coach screws for wall mounting
instead of U bolts and nuts.

GK Enclosure
Pipe Mounting

For C6D range surface / wall mounting bracket

is not available.
Pipe mounting bracket can be used for surface /
wall mounting.

Range Code : C6D only #

GM / GA Enclosure

GK Enclosure
Pipe Mounting

Pipe Mounting

Note : Dimensions for Model 304 / 384 are different. Ask for applicable drawing.

All dimensions are in mm

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0503 DPS 301Rev.1

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Pressure Switch, Differential Pressure Switch, Indicator, Transmitter,...e, Humidity, Flow, Level, Process Control - Switzer Instrument Limited

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