Ordering
When ordering, please give name and type reference, e.g.:
Room hygrostat
QFA1001
Mode of operation
The room hygrostat acquires the relative humidity of the ambient air via its humidity
measuring element, which is made of stabilized plastic texture. This plastic band actu-
ates a microswitch depending on the relative humidity. The microswitch has a fixed
switching differential X
Sd
and a potential-free contact output. If the actual humidity devi-
ates from the adjusted setpoint, the hygrostat switches the humidification or dehumidifi-
cation equipment as shown in the following function diagram.
w
S1
1
2
3
X
Sd
t
t
x
r. F.
[%]
1518D01d
e
Legend:
r. h.
Relative humidity in %
S1
Microswitch
1-2
Humidification
1-3
Dehumidification
w
Setpoint = upper switching point
x
Actual value
X
Sd
Switching differential
t
Time
Due to the measuring element’s aging effect, the switching point drifts slowly and con-
stantly. For this reason, recalibration may be required in due time.
At temperatures other than the calibration temperature, the switching point drifts sys-
tematically (temperature influence). Also, in the case of fast humidity changes, the
switching point will temporarily be shifted.
Mechanical design
The room hygrostat is designed for wall mounting. It fits on most commercially available
recessed conduit boxes. The cables are introduced either from the rear (recessed con-
duit boxes) or from above (surface-run wires), after knocking out the cable inlet
tongues.
The unit consists of base and cover.
Base and cover can be separated (snap-on connection).
The base accommodates the humidity measuring element, setpoint setting element
with setting spindle, scale, microswitch and screw terminals.
The cover carries the removable setpoint knob with its imprinted scale.
This model is of the same basic design as the QFA1001, but there is no external
setpoint knob. The setpoint can only be adjusted when the cover is removed.
Function diagram
QFA1001
QFA1000
2/4
Siemens
Room hygrostats QFA1001, QFA1000
CE1N1518en
Building Technologies
2014-07-30
