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Technical Instructions Document No. CA1N1552E-P25 November 24, 2003 QBM81-… Differential Pressure Switch Description Differential pressure switch for monitoring air pressure in HVAC systems. Features • Monitors air filters, airflow and fan belts • Can be used to monitor pressure in clean rooms, kitchens, etc. • Easy to mount Application The QBM81-... Differential Pressure Switches are used to monitor differential pressure, underpressure and overpressure in HVAC installations. By measuring differential pressure, they monitor the state of air filters, prevailing airflows, damaged fan belts and overpressure in clean rooms, kitchens, etc. They are also used to monitor differential pressure and positive and negative relative pressure in HVAC systems. Product Numbers There are three differential pressure switches available that measure various pressure ranges: Table 1. Product Numbers. Ordering Product Number Pressure Range (Inches WC) QBM81-3 0.08 to 1.20 QBM81-5 0.20 to 2.00 QBM81-10 0.40 to 4.00 If required, FK-PZ... duct probes must be ordered separately. When placing an order, specify the quantity, product number and description. Example: 1 QBM81-5 Differential Pressure Switch and one set of FK-PZ2 duct probes Siemens Building Technologies, Inc. Technical Instructions Document Number CA1N1552E-P25 November 24, 2003 Operation QBM81-… Differential Pressure Switch The differential pressure between the two pressure connections deflects a springloaded diaphragm. This special diaphragm ensures long-term stability of switching points. Each type is engraved with individual scales for highly accurate adjustment. The options for adjustment are shown in Figure 2. Switch State XD 1 2 3 SMIS0077R1 1 1 2 3 0 ∆p W Figure 1. Operation Diagram. Switching Points Cut-in Pressure (in WC) min. 1.20 Cut-in Pressure (in WC) Switching Differential min. 2.00 max. Cut-in Pressure (in WC) max. 1.60 2.40 1) 1) max. 3.20 1.20 0.80 min. 4.00 1) 0.80 1.60 0.40 0.80 Pressure Range 0.08 to 1.20" WC ∆p in WC Pressure Range 0.20 to 2.00" WC 0.24 0.16 0.08 0 0 0.16 0 0.08 ∆p in WC 0 0.12 0.08 0.04 0 0 SMIS0078R2 0.40 ∆p in WC Pressure Range 0.40 to 4.00" WC 1. Factory Setting Figure 2. Switching Points. Mechanical Design The QBM81-... Differential Pressure Switch consists of: • Housing and cover • Diaphragm • One sheet-steel mounting bracket Connection kit (supplied with each switch) consists of: • Two duct adapters • Four fixing screws • 6.6 feet (2 m) tubing, ø 0.25 inch Page 2 Siemens Building Technologies, Inc. QBM81-… Differential Pressure Switch Accessories Technical Instructions Document Number CA1N1552E-P25 November 24, 2003 For difficult conditions or cases where high-precision measurements are required, two other kits are available: FK-PZ1 Set of two duct probes (nickel-plated iron) with rubber grommet FK-PZ2 Set of two duct probes (aluminum) with aluminum mounting rosettes and four mounting screws Mounting Notes Mounting instructions are enclosed with the pressure switch. NOTE: Mounting positions other than vertical affect the cut-in pressure. See Commissioning Notes. The pressure switch is suitable for mounting on air ducts or walls. The recommended orientation is vertical, but any orientation is acceptable. The pressure connection tubes can be of any length, but the response time will increase if they are longer than 6.6 feet (2 meters). The pressure switch should be mounted so that it is above the pressure connection points. To prevent the accumulation of condensation, the tubing must be routed so that there is a gradual incline from the pressure connection points to the pressure switch (no looping). Commissioning Notes The required setpoint can be selected on the setpoint knob located under the cover. See Dimensions, Item 5. NOTE: The setpoint scale provided with the unit is metric. The pressure switch is factory-calibrated in the vertical position. If installed horizontally, this will affect the switching point as follows: Specifications Electrical Interface • With cover facing upwards: Switching point is 0.044" WC higher than scale. • With cover facing downwards: Switching point is 0.044" WC lower than scale. Type of switch Contact rating Operating voltage Switching differential (∆p)* Reset Service life Product Data Measuring range Repeatability Range 0.08 to 1.20 in WC Range 0.20 to 4.00 in WC Maximum overload on one side Admissible media Siemens Building Technologies, Inc. Single-pole change-over, multi-layer contact 24 Vac/dc, >0.01 A 250 Vac Maximum 5 A resistive Maximum 3 A inductive, cos ϕ >0.6 (0.8 A starting current sixfold, cos ϕ > 0.6 Maximum 250 Vac Adjustable Automatic >1,000,000 switching operations See Product Numbers <± 0.10 in. WC <± 0.02 in. WC 20.07 in. WC Air and non-corrosive gases Page 3 Technical Instructions Document Number CA1N1552E-P25 November 24, 2003 QBM81-… Differential Pressure Switch Housing Cover Diaphragm Mounting bracket Duct adapters Tubing Fiberglass reinforced polycarbonate Polycarbonate Silicone (low-swell rubber, no ABS) Sheet-steel (galvanized) ABS PVC, soft Connections Electrical connection Cable entry Pressure connections 3 screw terminals PG11 cable gland Male, ø 0.24-inch Weight and Dimensions Weight (including packaging) Dimensions 0.42 lb. with mounting bracket See Figures 5 and 6 General Ambient Conditions Ambient temperature Operation Storage Ambient humidity –4°F to 185°F (–20°C to 85°C) –40°F to 185°F (–40°C to 85°C) <90% rh (non-condensing) Mounting Orientation Any. See Commissioning Notes. Agency Approvals Protection class Class 2 Protection standard IP54 to IEC529 Combustion class to UL94 Pressure casing and housing V-0 Cover HB Plastic tubing V-2 Duct adapters HB Conforms to CE requirements * The switching differential is factory-set to a fixed value (See Figure 2), and the adjustment screw is sealed with paint (approximately one turn counterclockwise from the end-stop). Specifications, Continued Materials SMIS0079R1 Wiring Terminals 1 Ph 2 SWITCH CONNECTS 1-2 ON PRESSURE FALL 3 SWITCH CONNECTS 1-3 ON PRESSURE RISE ∆p Figure 3. Wiring Terminals. SMIS0080R1 Application Examples ∆p + ∆p – – + + Pressure upstream of filter – Pressure downstream of filter + Pressure downstream of filter – Pressure upstream of fan on inlet side or open to atmospheric pressure. With radial fans, locate at inlet center Figure 4. Application Diagram. Page 4 Siemens Building Technologies, Inc. QBM81-… Differential Pressure Switch Technical Instructions Document Number CA1N1552E-P25 November 24, 2003 Dimensions All dimensions in inches (millimeters) 3.52 (89.4) 1.75 (44.4) 0.98 (25) 1.58 (40) 3.60 (91.4) 0.87 (22) 1 2.01 (51) 5 2 3 ø0.24 (ø6.2) 3.47 (88) 0.75 (19) P2 ø3.19 (ø81) P1 SMIS0081R1 4 Legend: 1 Mounting bracket 2 P1 connection, higher pressure 3 P2 connection, lower pressure 4 Pressure differential scale (factory-sealed with paint) 5 Setpoint knob Figure 5. QBM81-… Differential Pressure Switch Dimensions. ø0.26 (ø6.5) 3.09 (78.5) 2.36 (60) SMIS0082R1 2 x ø0.13 (2 x ø3.4) ø0.63 (ø16) ø0.26 (ø6.5) Figure 6. Duct Adapter Dimensions. NOTE: Two duct adapters are supplied with the pressure switch. 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. Other product or company names mentioned herein may be the trademarks of their respective owners. © 2003 Siemens Building Technologies, Inc. Siemens Building Technologies, Inc 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 [email protected] Document No. CA1N1552E-P25 Printed in the U.S.A. Page 5