Siemens QFA1000 Owner's manual

QFA1000, QFA1001
Technical Instructions
Document No. 155-708
July 19, 2010
Room Hygrostats
QFA1001
QFA1000
Siemens Industry, Inc.
Description The room hygrostats are used for controlling and monitoring relative humidity in
ventilation or air conditioning facilities. They ensure room humidity control within the
selectable range of 30 to 90% relative humidity by controlling humidification or
dehumidification equipment. They can also be used for monitoring minimum or
maximum humidity levels.
Features •Hygrostat with single-pole microswitch
•Humidity measuring element made of stabilized plastic
•Setpoint knob for the upper switching point
•Mounts directly on the wall or on a recessed conduit box
Application •For controlling humidification equipment
•For controlling dehumidification equipment
Product Numbers
Switching Differential1
Product
Number Setpoint Setting Range Statically Dynamically
Setpoint
Adjustment
QFA1000 Internally
QFA1001 30 to 90% rh Approx. 4% rh 6% rh Externally
1) The static switching differential is determined at a constant ambient humidity by
turning the setting knob.
The dynamic switching differential is determined by changing the ambient humidity
while maintaining the same setpoint adjustment; only the dynamic switching
differential is of practical value.

Technical Instructions QFA1000, QFA1001 Room Hygrostats
Document Number 155-708
July 19, 2010
Page 2 Siemens Industry, Inc.
Mode of Operation The hygrostat acquires the relative humidity of the ambient air with its humidity
measuring element, which is a stabilized, plastic strip. The strip actuates a microswitch
with a fixed switching differential Xdand a potential-free contact output (SPDT),
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
(Figure 1).
Figure 1. Function Diagram.
rh Relative humidity in %
S1 Microswitch
1−2 Humidification
1−3 Dehumidification
w Setpoint
x Actual value
X
dSwitching differential
t Time
Due to the measuring element’s aging effect, the switching point drifts slowly and
constantly. For this reason, recalibration may be required in due time.
At temperatures other than the calibration temperature, the switching point drifts
systematically (temperature influence). Also, in the case of fast humidity changes, the
switching point will temporarily be shifted.
Mechanical Design
QFA1001
The room hygrostat is designed for wall mounting, and fits on most commercially
available recessed conduit boxes. The cables are introduced either from the rear
(recessed conduit boxes) or from above (surface-run wires), after removing the knock-
outs.
The unit consists of base and cover that 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.
QFA1000 This model has the same basic design as the QFA1001, but without an external
setpoint knob. The setpoint can only be adjusted when the cover is removed.

QFA1000, QFA1001 Room Hygrostats Technical Instructions
Document Number 155-708
July 19, 2010
Siemens Industry, Inc. Page 3
Operating Elements
1 Setpoint knob with scale – only with QFA1001
2 Setpoint setting spindle
3 Scale for setpoint adjustment with QFA1000
Figure 2. Operating Elements.
Mounting Notes
Mounting Choices
The base has cable entries at the rear for mounting the room hygrostat on recessed
conduit boxes. For wall mounting, appropriate holes at the top or bottom can be
knocked out.
Mounting Location The hygrostat should be mounted on an inner wall approximately 4.9 feet (1.5 m) above
the floor and at least 1.6 feet (0.5 m) from the closest wall.
Mount the unit where there is a natural circulation of room air (do not mount near drafts,
in corners, behind curtains, too close to doors and windows, or on an outer wall).
Sources of heat and refrigeration (radiators, computers, televisions, concealed heating
pipes, hot or cold water pipes) must be at an adequate distance.
The hygrostat should not be exposed to direct sunlight.
Mounting Instructions Installation Instructions for the room hygrostat are available online.
Specifications
Functional data
Setpoint range 30 to 90% rh
Temperature operating range 32°F to 122°F (0°C to 50°C)
Humidity measuring element Stabilized plastic band
Control mode Two-position
Time constant (v = 0.2 m/s) Approximately 5 minutes
Switching differential See Product Numbers
Setting accuracy +5% rh (can be improved by
calibrating on site)
Temperature influence +0.5% rh/K
Humidity calibration at 55% rh, 73°F (23°C)
Long-term stability Approximately −1.5% rh/a
Type of switch Potential-free microswitch (SPDT)
Contact rating
Maximum 5 (3) A, 24 Vac/Vdc
Minimum 100 mA, 24 Vac/Vdc
Protective data Degree of housing protection P 20 to EN 60 529
Safety class II to EN 60 730
Electrical connection Screw terminals for Maximum 2 × 16 AWG

Technical Instructions QFA1000, QFA1001 Room Hygrostats
Document Number 155-708
July 19, 2010
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. 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.[email protected]
Materials and colors Base PPS, Fortron, fiberglass reinforced,
Black
Cover PC Lexan 940, pure-white
Humidity measuring element Plastic
Standards conformity
EMC directive 89/336/EEC
UL UL873
cUL Canadian Standard C22.2 No. 24-93
Weight QFA1001 3.17 ounces (0.090 kg)
QFA1000 3.17 ounces (0.090 kg)
Wiring Diagrams
Internal Diagram
1-2 Humidification
1-3 Dehumidification
Wiring Diagrams
Figure 3. Humidification.
Figure 4. Dehumidification.
Dimensions
Figure 5. Dimensions in Inches (Millimeters).
Document No. 155-708
Printed in the U.S.A.
Page 4