InstrumentationPressure Measurement

Piping of differential pressure and flow transmitters


In this session we are gonna discuss about how to connect differential pressure & flow transmitters to the several process


  • Check of high/low pressure sides of transmitter

    The detecting unit of the differential pressure transmitter bears symbols H and L which represent high and low pressure sides, respectively. Also, vent/drain plugs are provided at the lower process connection, while impulse pipes are connected at the upper process connections.

  • Flow measurement (in case of gas)

    Place the transmitter above the differential pressure source.

  • Flow measurement (in case of liquid)

    Place the transmitter below the differential pressure source. Make piping so that gas in the impulse pipe is not delivered to the transmitter, and incorporate gas reservoirs as required.

  • Flow measurement (in case of steam)

    Set two condensers at the same height near the process tap. Fill the line between the condensers and transmitter
    with condensed water. Install a drain port as required.

  • Pressure measurement (in case of liquid)

    Zero point can be checked with a manifold valve installed.

  • Pressure measurement (in case of gas)

    Mount the transmitter above the process pipes to preventing moisture from entering the inside of transmitter.

  • Level measurement

    1) In case of wet leg:

    For measurement, connect the highest liquid level tapping of tank with the low pressure side of transmitter, and the lowest liquid level tapping of tank with the high pressure side of transmitter.
    Level calculation formula
    LRV : ρH2 – ρ0H1
    URV : ρH2 + ρ1h – ρ0H1
    Span (ΔP): ρ1h
    LRV : Low limit of measurement (0% point)
    URV : High limit of measurement (100% point)
    ρ0,ρ,ρ1: Density
    H1, H2: Liquid level,
    h: Liquid level change

  • 2) In case of dry leg:

    For an open tank, leave the low pressure side of transmitter open to atmosphere.
    Level calculation formula
    LRV: ρH1
    URV: ρH1 + ρ1h
    Span (DP): ρ1h
    LRV: Low limit of measurement (0% point)
    URV: High limit of measurement (100% point)
    ρ,ρ1: Density
    H1: Liquid level, h: Liquid level change

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