DIFFERENTIAL PRESSURE TRANSMITTERS TECHNICAL REQUIREMENTS FOR IAS

This article is about general and technical requirements for differential pressure transmitter (DP Transmitter) used in Integrated Automation System or Building Automation System.

DIFFERENTIAL PRESSURE TRANSMITTERS TECHNICAL REQUIREMENTS FOR IAS

  1. General DP performance requirements

    1. Pressure transmitters shall be constructed to withstand 100% pressure over-range without damage and to hold calibrated accuracy when subject to a momentary 40% over-range input.
    2. Pressure transmitters shall provide the option to transmit a 0 to 5V dc, 0 to 10V dc, or 4 to 20 mA output signal.
    3. Differential pressure transmitters used for flow measurement shall be sized to the flow sensing device and shall be supplied with shutoff and bleed valves in the high and low sensing pick-up lines (3 valve manifolds).
    4. Provide a minimum of a NEMA 1 housing for the transmitter. Locate transmitters in accessible local control panels wherever possible. Provide tubing with rubber or neoprene grommet from panel to expose room conditions when necessary.
    5. Low air pressure, differential pressure transmitters used for room pressurization control (i.e. laboratories, OR’s clean rooms, etc.) shall be equipped with a LED display indicating the transmitter output signal.
    6. Duct sensing pressure applications where the velocity exceeds 1500 fpm shall utilize a static pressure traverse probes.

  2. Liquid, Steam and Gas:

    1. General: Two-wire smart DP cell type transmitter, 4-20 mA or 1-5 VDC linear output, adjustable span and zero, stainless steel wetted parts.
    2. Ambient Limits: –40 to 175 degrees F (-40 to 121 degrees C), 0 to 100% RH.
    3. Process Limits: –40 to 400 degrees F (-40 to 205 degrees C).
    4. Accuracy: Less than 0.1 percent.
    5. Output Damping: Time constant user selectable from 0 to 36 seconds.
    6. Non-interactive zero and span adjustments adjustable form the outside cover.
    7. Vibration Effect: Less than +/- 1 percent of upper range limit from 15 to 2000 Hz in any axis relative to pipe mounted process conditions.
    8. Electrical Enclosure: NEMA 4, 4X, 7, 9.
    9. Approvals: FM, CSA.
    10. Acceptable Manufacturers: <Confirm list>
      • Honeywell
      • Foxboro
      • Setra
      • Rosemount Inc. 3051 Series
      • Approved equal
  3. General Purpose Low Pressure Air (0 – 125 Pa): Generally for each measurement of duct pressure, filter differential pressure or constant volume air velocity pressure measurement where the range is applicable. The pressure transmitter shall be capable of transmitting a linear electronic signal proportional to the differential of the room and reference static pressure input signals with the following performance requirements.
    1. General: Loop powered two-wire differential capacitance cell-type transmitter immune to shock and vibration
    2. Switch shall be capable of Automatic Rest
    3. Output: Two wire 4-20 mA output with zero adjustment.
    4. Overall Accuracy: Plus or minus 0.5 percent of full scale
    5. Dead Band: Less than 0.3% of output
    6. Repeatability: Within 0.2% of output
    7. Linearity: Plus or Minus 0.2% of span
    8. Response: Less than on second for full span input.
    9. Temperature Stability: Less than 0.05% of output shift per degree C change.
    10. Minimum Range: 1 inches w.c.
    11. Maximum Range: 10 inches w.c.
    12. Housing: Polymer housing suitable for surface mounting.
    13. Static Sensing Element: Pitot-type static pressure sensing tips similar to Dwyer model A-301 and connecting tubing.
    14. Range / Span: Select for specified setpoint to be between 25 percent and 75 percent full-scale. Not greater than two time the design space DP
    15. Magnehelic Gauges: Provide Dwyer Series 200 Magnehelic Differential Pressure Gauge (or equal) for each DP transmitter.  Provide gauge, mounting bracket, ¼ inch aluminum tubing, static pressure tips, and molded plastic vent valves for each gauge connection.  Select range for specified recommended filter loading pressure drop to be 75 percent full-scale.  For other DP transmitters select range for specified setpoint to be between 25 percent and 75 percent full-scale
    16. Acceptable Manufacturers: <Confirm list>
      • Setra
      • Modus T30
      • Veris PX Series
      • Dwyer Series 616
      • Approved equal
  4. Medium to High Air Pressure Applications (125Pa to 2500 Pa) : The pressure transmitter shall match the characteristics defined for low air applications with the modified performance criteria:
    1. Zero and Span (% F.S./ Deg C) shall be 0.05% including linearity, hysteresis and repeatability.
    2. Accuracy: 1% Full Scale (best straight line)
    3. Static Pressure Effect: 0.05% Full Scale (to 700 KPA)
    4. Thermal Effects: less then +/- 0.05% Full Scale / Deg C over 5C to 40C when calibrated at 22 deg C.
    5. Pressure switches shall be manually reset.
  5. General Purpose Low Pressure/Low Differential Air: Generally for use in static measurement of space pressure or constant volume air velocity pressure measurement where the range is applicable.
    1. General: Loop powered, two-wire differential capacitance cell type transmitter.
    2. Output: Two-wire 4-20 mA output with zero adjustment.
    3. Overall Accuracy: Plus or minus 1 percent.
    4. Minimum Repeatability: +/- .25 percent of reading.
    5. Maximum Range: 1, 0.25, or 0.5 inches w.c.
    6. Housing: Polymer housing suitable for surface mounting.
    7. Acceptable Manufacturers: <Confirm list>
      • Setra
      • Modus T30
      • Honeywell
      • Approved equal
    8. Static Sensing Element: Pitot-type static pressure sensing tips similar to Dwyer model A-301 and connecting tubing.
    9. Range: Select for specified setpoint to be between 25 percent and 75 percent full-scale.
  6. VAV Velocity Pressure: Generally for use in variable volume air velocity pressure measurement where the range is applicable.
    1. General: Loop powered two-wire differential capacitance cell type transmitter.
    2. Output: Two-wire, 4-20 mA output with zero adjustment.
    3. Overall Accuracy: Plus or minus 0.25 percent.
    4. Minimum Range: 0 inches w.c.
    5. Maximum Range: 1 inch w.c.
    6. Housing: Polymer housing suitable for surface mounting.
    7. Acceptable Manufacturers: <Confirm list>
      • Setra
      • Approved equal
    8. Range: Select for minimum range that will accept the maximum velocity pressure expected.

Magnehelic Gauges:  Provide Dwyer Series 200 Magnehelic Differential Pressure Gauge (or equal) for each DP transmitter.  Provide gauge, mounting bracket, ¼ inch aluminum tubing, static pressure tips, and molded plastic vent valves for each gauge connection.  Select range for specified setpoint to be between 25 percent and 75 percent full-scale.

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