Page 1
TM
Powers
Controls
SW 141 Differential Static
Airflow Switches
Technical Instructions
Document No. 155-052P25
SW 141-1
June 17, 2010
Description
Application
Product Numbers
141-0518
The SW 141 Airflow Switch senses static differential pressure and the diaphragm operated
snap switches actuate electrical circuits. Auto reset and manual reset models are
available.
Auto reset switches (141-0518 and 141-0574) should be used for applications requiring
positive proof of airflow (or fan operation) or to detect high differential pressures
associated with dirty air filters or similar maintenance alarms not requiring safety lock-out
(shut down) of the fan.
The manual reset switch (141-0575) should be used for applications requiring safety lock
out (shut down) of the fan. The switch can be used on the fan discharge (positive
pressure), fan inlet (negative pressure), or across the fan (differential pressure) to detect
excessively high positive pressures or low negative pressures, and turn off the fan before
damage occurs to ducts or dampers.
Table 1.
Product
Number
141-
0518
141-
0575
141-
0574
Setpoint Range
(Field Adjustable)
1” to 12” WC
(250 Pa to 3000 Pa)
1” to 12” WC
(250 Pa to 3000 Pa)
0.05” to 1.0” WC
(12.5 Pa to 250 Pa)
Setpoint *
Accuracy
@ 12” ± 1.5” WC
(3000 Pa ± 375 Pa)
@ 12” ± 1.5” WC
(3000 Pa ± 375 Pa)
@ 1”±0.2“ WC
(250 Pa ± 50 Pa)
Switching *
Differential
Approx.
0.6” to 1.5” WC
(150 Pa to 375 Pa)
Not Applicable SPST/
Approx.
0.06" to 0.6” WC
(15 Pa to 150 Pa)
Switching
Action
SPDT/
Auto Reset
Manual
Reset
SPDT/
Auto Reset
* Setpoint accuracy tolerance and switching differential decrease proportional to setpoint decrease.
Siemens Industry, Inc.
Page 2
Technical Instructions SW 141 Differential Static Airflow Switches
Document Number 155-052P25
June 17, 2010
Specifications
Operating
Physical
Accessories
Measured media Air
Switch action
Auto reset See Table 1
Manual reset Switch is Normally Closed (N.C.) and
only opens on increasing pressure signal.
Switch must be manually reset by operator
Ambient temperature range −40°F to 180°F (−40°C to 82°C)
Maximum overpressure 0.5 psi (3.4 kPa)
Mounting position Diaphragm in any vertical plane
Electrical ratings Non inductive - 15 amps @
120-277 Vac
Pilot Duty - 300 VA @ 120-277 Vac
Conduit opening One, conduit size 1/2-inch
Sample line connectors Two connectors, complete with nuts and
ferrules, which accept 1/4-inch OD (6.4 mm)
copper or poly tubing
Material Aluminized steel
Agency certification
U.L. MFHX File MH9888
CSA 1811M25
Weight 1 lb (0.45 kg)
Dimensions See Figure 9
High accuracy static pressure sensor 269-062
Static pressure sensing kit 189-142
Operation
Installation
The diaphragm operates a spring lever to actuate the snap switch. The manual reset
switch keeps the electrical contact open until pushed to reset. Turning the adjustment
knob clockwise increases the setpoint.
Mount the unit with the diaphragm in any vertical plane. Connect the static pressure
line(s) as shown in Figure 1.
Switch
SW0097R1
Figure 1. Connecting the Static Pressure Line.
Nut & Integral
Ferrule
Tubing
Page 2 Siemens Industry, Inc.
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SW 141 Differential Static Airflow Switches Technical Instructions
Document Number 155-052P25
June 17, 2010
Installation,
Continued
For use as a negative pressure switch:
Connect the static pressure line to the low inlet (marked on the case and Figure 2)
and leave the high inlet open to the atmosphere.
For use as a positive pressure switch:
Connect the static pressure line to the high inlet (marked on the case and Figure 2)
and leave the low inlet open to the atmosphere.
For use as a differential pressure switch:
Connect the highest static pressure line to the high inlet and the lowest static
pressure line to the low inlet (marked on the case and Figure 2.)
Setpoint
Adjustment
141-0518 141-0574 141-0575
Figure 2. Switches with Covers Removed.
Each switch is factory set at the minimum setpoint. See Table 1.
1. To increase the setpoint, turn the adjustment screw clockwise as shown in Figure 2
and Figure 3. From the lowest setpoint, several turns are necessary to engage the
adjusting mechanism.
2. Adjust the setpoint until switching occurs at the required point.
3. Check the setpoint for accuracy with a magnahelic gauge.
The Red Band Is
The Setpoint
Location On The Scale
SW0096R1
3.0
9.0
"
WC
.05
6.0
12.0
Figure 3. Adjusting the Setpoint.
Siemens Industry, Inc. Page 3
Page 4
Technical Instructions SW 141 Differential Static Airflow Switches
Document Number 155-052P25
June 17, 2010
Pressure Sensors
Wiring Diagrams
Pressure sensor selection is based on the medium to be measured, the measurement
type (static or velocity), and the required range and accuracy.
Pressure sensors measure the difference between two sensing ports usually labeled high
and low. This provides a pressure measurement against a reference. Measuring the
pressure inside a pipe or duct and comparing it to the air outside (ambient) the pipe or
duct is an example of static pressure measurement. A sensor measuring the pressure
differential across a pump or chiller measures velocity pressure.
Figure 4. Pitot Tube (Part Number 269-062).
Before setpoint pressure is applied to the diaphragm, the switch contact is in a normally
closed position as shown in Figures 5 and 6.
.
Figure 5. Manual Reset Switch 141-0575.
Figure 6. Auto Reset Switches 141-0518 and 141-0574.
SPDT terminals are marked Common (C), Normally Open (NO), and Normally
Closed (NC).
Figure 7. Auto Reset Switches to Prove Excessive Airflow or Pressure.
Page 4 Siemens Industry, Inc.
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SW 141 Differential Static Airflow Switches Technical Instructions
Document Number 155-052P25
June 17, 2010
Wiring Diagrams,
Continued
Figure 8. Auto Reset Switches to Prove Insufficient Airflow or Pressure.
Dimensions
6.13
(156)
SW000098R1
2.81
(71)
3.25
(82)
1.94 (49)
3.88
(98)
1.63
(41)
0.44
(11)
0.19
(5)
dia
hole
High
Pressure
Inlet
0.78
(20)
1.38
(35)
3.25
(82)
0.71
(18)
Low
Pressure
Inlet
Figure 9. Dimensions in Inches (Millimeters).
Information in this publication is based on current specifications. The company reserves the right to make changes in specifications and models as
design improvements are introduced. Powers is a registered trademark of Siemens Industry, Inc. Other product or company names mentioned
herein may be the trademarks of their respective owners. © 2010 Siemens Industry, Inc.
Siemens Industry, Inc.
Building Technologies Division
1000 Deerfield Parkway
Buffalo Grove, IL 60089-4513
U.S.A.
Your feedback is important to us. If you have
comments about this document, please send them
to SBT_technical.editor.us.sbt@siemens.com
Document No. 155-052P25
Printed in the U.S.A.
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