Siemens QFM81 Series Technical Instructions

QFM81 Series
Duct Hygrostats
Description
Features
Application
Product Numbers
Mode of Operation
QFM81.21
On /off hygrostat with microswitch, and temperature-compensated humidity sensor for
temperature-independent humidity measurements.
• Stabilized sensing strip (good linearity, very stable even at high humidity, insensitive
to dust and contaminated air).
• Can be mounted in ventilating ducts or rooms.
For controlling humidification equipment and dehumidification equipment.
Product Setpoint Range
Number
QFM81.2 15 to 95% r.h.
QFM81.21
NOTE: Includes a mounting flange (for duct or wall mounting) and a sealing ring (for
duct mounting).
The hygrostat acquires the relative humidity of the air with its humidity sensor, which is
a stabilized, plastic strip. The strip actuates a microswitch with a fixed switching
differential X and a potential-free contact output (SPDT), depending on the relative
d
humidity of the air. If the actual humidity deviates from the adjusted setpoint, the
hygrostat switches the associated humidification or dehumidification equipment on or
off as shown in the following function diagram (Figure 1).
Technical Instructions
Switching
Differential
(W )
h
(X )
d
Approx. 4% rh
Document No. 155-707
April 21, 2010
QFM81.2
Degree of
Protection Adjustment
IP 30
IP 55
Siemens Industry, Inc.
Setpoint
Externally
Internally