Siemens QFM81 Series Betriebsanleitung

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

(Wh) Switching

Differential

(Xd)

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 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).

Technical Instructions QFM81 Series Duct Hygrostats

Document Number 155-707

April 21, 2010

Page 2 Siemens Industry, Inc.

r. h. [%]

SEN0507R1

Figure 1. Function Diagram.

rh Relative humidity in %

S1 Microswitch

1−2 Humidification

1−3 Dehumidification

w Setpoint

x Actual value

dSwitching 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 Xd, 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

<5m/s

>5m/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 AWGmaximum

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 – 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.

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]

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)

A B

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

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