Siemens QFA81 User Manual
1
513
Room Hygrostats QFA81...
Switching
differential (Xd)
approx. 4 % r.h.
approx. 4 % r.h.
for relative humidity
QFA81.1 QFA81
On/off hygrostat with microswitch,
with humidity sensor,
with plastic texture sensing strip (good linearity, wide measuring range),
for the control of humidification equipment,
for the control of dehumidification equipment,
for direct wall mounting or mounting on recessed conduit boxes
Use
Type summary
Ordering
Mode of operation
The hygrostats are designed for controlling and monitoring the relative humidity in ventilating and air conditioning plants.
They control the humidity content of the room air within an adjustable range of 30 to
100 % r.h.
They can also be used for monitoring a minimum or maximum humidity level.
Type reference Setpoint range (Wh)
QFA81 30…100 % r.h.
QFA81.1 30…100 % r.h.
When ordering, please give name and type reference; for example:
room hygrostat QFA81
The hygrostat acquires the relative humidity of the room air with its plastic texture sensing strip. The strip actuates a microswitch with a fixed switching differential Xd and a
potential-free contact output (S.P.D.T.), depending on the relative 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.
Setpoint
adjustment
externally
internally
Siemens Building Technologies CM1N1513E / 02.1999
Landis & Staefa Division 1/4
Function dia
g
ram
r. h.
w
[%]
d
X
x
1513D01E
Mechanical design
QFA81
S1
t
4
1
2
t
r.h. Relative humidity in %
S1 Microswitch
1−2 Humidification
1−4 Dehumidification
w Setpoint
x Actual value
Switching differential
X
d
If the relative humidity exceeds the adjusted setpoint, the potential-free contact of the
microswitch will change over from 1−2 to 1−4. If the relative humidity falls by the amount
of the fixed switching differential X
, the contact will return to the position 1−2.
d
The hygrostat is designed for wall mounting. It can be fitted to most commercially available recessed conduit boxes. The cables can be introduced from the rear (concealed
wiring) or from above (surface-run wires) through knockout openings.
The unit consists of base and cover. Both snap together and can be detached again.
The base accommodates a printed circuit board which carries the humidity sensing
element (plastic texture strip), the setpoint adjusting element with the spindle, scale,
microswitch, and connection terminals.
The cover houses the detachable setpoint knob with the setting scale and a concealed
mechanical setpoint limitation facility.
QFA81.1
Setting elements
QFA81
Setpoint knob
Setpoint limitation
QFA81.1
Same design as the QFA81, but with a cover with no setpoint knob and no setpoint
limitation facility. The setpoint can be adjusted only when the cover is removed.
Using the setpoint knob, the setpoint can be adjusted in the range 30…100 % r.h.
After removal of the setpoint knob, the setpoint can be mechanically limited to a minimum or maximum value by appropriate setting of the tongues.
% rH
1 Tongue for minimum limitation of setpoint
2
1
2 Tongue for maximum limitation of setpoint
1513Z01
Setpoint spindle
CM1N1513E / 02.1999 Siemens Building Technologies
2/4 Landis & Staefa Division
The setpoint can only be changed with the spindle after removal of the cover.
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