QFM81 Series Technical Instructions Document No. 155-707 April 21, 2010 Duct Hygrostats QFM81.21 QFM81.2 Siemens Industry, Inc. Description On/off hygrostat with microswitch, and temperature-compensated humidity sensor for temperature-independent humidity measurements. Features • 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. Application For controlling humidification equipment and dehumidification equipment. Product Numbers Product Number Setpoint Range (W h ) Switching Differential (X d ) Degree of Protection Setpoint Adjustment QFM81.2 IP 30 Externally QFM81.21 15 to 95% r.h. Approx. 4% rh IP 55 Internally NOTE: Includes a mounting flange (for duct or wall mounting) and a sealing ring (for duct mounting). Mode of Operation 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 d and 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). Technical Instructions QFM81 Series Duct Hygrostats Document Number 155-707 April 21, 2010 Page 2 Siemens Industry, Inc. X d t t 1 3 2 w x S1 r. h. [%] SEN0507R1 Figure 1. Function Diagram. rh Relative humidity in % S1 Microswitch 1 − 2 Humidification 1 − 3 Dehumidification w Setpoint x Actual value X d Switching differential t Time If the relative humidity exceeds the adjusted setpoint, the potential-free contact of the microswitch will change over from 1 − 2 to 1 − 3. If the relative humidity falls by the amount of the fixed switching differential X d , the contact will return to the position 1 − 2. Mechanical Design QFM81.2 The hygrostat consists of a base with immersion sensor stem and cover. The cover is secured to the base with a screw. The stem accommodates the temperature-compensated humidity sensing element (stabilized plastic strip). The strip is mechanically linked to the microswitch via a transfer lever. Transfer lever, microswitch, setpoint setting element and connection terminals for connecting the humidification or dehumidification equipment are mounted on a printed circuit board inside the base. The connection terminals are protected by a hinged cover to avoid direct access when the cover is removed. The cover has a hole for the setpoint knob. The hygrostat is designed for mounting in air ducts, but can also be mounted on a wall. For both mounting methods, a mounting flange is required, which is supplied with the unit. QFM81.21 Same design as the QFM81.2, but with an additional transparent cover on the hole for the setpoint knob, cable gland Pg 11, and seal under the unit cover. Setting Elements Setpoint knob On both units, the setpoint is adjusted with the setpoint knob. The setting scale is on the unit cover. With the QFM81.21, the setpoint can be adjusted only when the cover is removed. QFM81 Series Duct Hygrostats Technical Instructions Document Number 155-707 April 21, 2010 Siemens Industry, Inc. Page 3 Mounting Notes Air Duct Mounting If the duct hygrostat is used for control, it must be mounted in the exhaust air duct after the room to be controlled. If the duct hygrostat is used for monitoring the maximum or minimum humidity level, it imust be mounted in the supply air duct. Mounting Positions The immersion sensor stem must be mounted either horizontally or vertically with the stem pointing downward. Do not mount with the stem pointing upward. To ensure accurate humidity measurements, it must be made certain that the air to be measured is sufficiently mixed at the point of measurement. SEN0508R1 SEN0509R1 <5 m / s > 5 m /s Figure 2. Acceptable Mounting Positions. The mounting orientation is dependent on the air velocity in the ductwork: at <5 m/s, the holes in the stem must face the airflow; at >5 m/s, they must be perpendicular to the direction of airflow (see Figure 2). Minimum immersion length When mounting the hygrostat in air ducts, the minimum immersion length of the stem 5.12 inches (130 mm) must be observed. The mounting flange supplied with the unit allows the immersion length to be adjusted between 5.12 inches (130 mm) and 6.14 inches (156 mm). Wall Mounting 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. For wall mounting, the mounting flange supplied with the hygrostat must be used. Technical Instructions QFM81 Series Duct Hygrostats Document Number 155-707 April 21, 2010 Page 4 Siemens Industry, Inc. Specifications Setpoint range 15 to 95% rh Control mode On/off Switching differential Approximately 4% rh (fixed) Type of switch Potential-free microswitch (SPDT) Contact rating Maximum 5 (3) A, 24 Vac/Vdc Minimum 100 mA, 24 Vac/Vdc Temperature influence Compensated Long-term stability Approximately − 1.5% rh/a Balancing At 55% rh, 73°F (23°C) Time constant (v = 0.2 m/s) Approximately 3 minutes Permissible air velocity 10 m/s Permissible ambient temperature Operation 32°F to 158°F (0°C to 70°C) Storage/transport –22°F to 158°F ( − 30 to 70°C) Degree of protection QFM81.2 IP 30 to EN 60 529 QFM81.21 IP 55 to EN 60 529 Safety class II to EN 60 730 conformity to low-voltage directive 73/23/EEC UL UL873 cUL Canadian Standard C22.2 No. 24-93 Connection terminals for 20 AWG. minimum 2 × 16 AWG maximum Materials Sensing element Polymer Casing with stem PPS, Fortron 1140L6, fiberglass reinforced Cover PC Lexan 940 Transparent cover PC Makrolon 2014R, transparent (only with QFM81.21) Weight Approximately 12 ounces (0.34 kg) Maintenance Maintenance-free, can be recalibrated Wiring Diagram SEN0510R1 1 23 1 – 2 Humidification 1 – 3 Dehumidification Figure 3. Wiring Connections. QFM81 Series Duct Hygrostats Technical Instructions Document Number 155-707 April 21, 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.us.sbt@siemens.com Dimensions SEN0511R1 0.39 (10) 0.65 (16,5) ø 1.18 (ø 30) 1.64 (41,7) 5.51 (140) 2.87 (73) 2.52 (64) 5.12...6.14 (130...156) 0.83(21) AB Pg 11 9.69 (246) 0.22 (5,5) 1.06 (27) 0.22 (5,5) 2.13 (54) A - B 2.24 (57) 1.12 (28,5) 0.24 (6) 1.10 (28) 2.67 (68) 1.65 (42) 2.99(76) 2.13 (54) Figure 4. Dimensions in Inches (Millimeters). Document No. 155-707 Printed in the U.S.A. Page 5 Next >