Data Sheet for Product

Technical Instructions QBM81-… Differential Pressure Switch
Document Number CA1N1552E-P25
November 24, 2003
Operation
The differential pressure between the two pressure connections deflects a spring-
loaded diaphragm. This special diaphragm ensures long-term stability of switching
points.
Each type is engraved with individual scales for highly accurate adjustment. The
options for adjustment are shown in Figure 2.
Switch State
1
0
W
p
∆
XD
SMIS0077R1
1
2
3
1
2
3
Figure 1. Operation Diagram.
Switching Points
Cut-in Cut-in Cut-in
Pressure Switching Pressure Pressure
(in WC) Differential (in WC) (in WC)
1.20
0.80
0.40
0
0
0.04 0.08 0.12
∆
p
in WC
1)
SMIS0078R2
2.40
1.60
0.80
0
0
0.08
0.16
0.24
∆
p
in WC
1)
4.00
3.20
0.80
0.40
0
0
0.08
0.16
∆
p
in WC
1.20
1.60
2.00
1)
min. max.
min. max. min. max.
Pressure Range Pressure Range Pressure Range
0.08 to 1.20" WC 0.20 to 2.00" WC 0.40 to 4.00" WC
1. Factory Setting
Figure 2. Switching Points.
Mechanical Design
The QBM81-... Differential Pressure Switch consists of:
• Housing and cover
• Diaphragm
• One sheet-steel mounting bracket
Connection kit (supplied with each switch) consists of:
• Two duct adapters
• Four fixing screws
• 6.6 feet (2 m) tubing, ø 0.25 inch
Page 2 Siemens Building Technologies, Inc.