Meriam MFT 4010 Modular Calibrator_HART Communicator - Manual (Page 20)

15
Differential Pressure Calibration
Differential pressure gauges and transmitters can be calibrated using xDN or xGI sensor modules. The
following drawing depicts a typical calibration set-up. The units under test should be isolated from the process
and drained of liquids if necessary. The low-pressure port of the DP unit under test is vented to atmosphere. Do
not connect the low-pressure port of an xDN sensor to the low-pressure port of the DP unit under test. Such a
dead end connection can cause errors due to the expansion or contraction of trapped gas as a function of
temperature change.
Meriam does not recommend using process pressure as the pressure source for DP pressure device
calibration. Errors in measurement and calibration can easily creep in if the pressure source is unstable. In
addition, xDN sensors have a maximum overpressure limit of 150 PSI when a three-valve equalizing manifold is
used properly. Sensor damage can occur if more than 15 PSI is applied to the high or low side of an xDN0020
or xDN0200 sensor through improper use of the equalizing manifold.
Additional DP Application Information
In addition to reading gauge pressures, the MFT can also be used to measure
the pressure drop across a device in a pressurized pipe. Examples include
measuring the differential pressure across positive displacement meters, filters,
orifice plates or valves. Process compatibility and pressure ranges of the sensor
modules need to be considered for each application.
A three valve equalizing manifold or push-to-read equalizing valve should be
used to avoid damaging xDN sensors. Follow the specific operating procedure
for each type of valve manifold.
3-Valve Manifold: Make sure all shut-off valves are closed. Connect to the
process. Slowly open the equalizing valve. Slowly open the high pressure
valve and then the low pressure valve. Close the equalizing valve and take
the measurement. Reverse the process to disconnect.
Push-to-read valve: Connect to the process. Open shut off valves. Push the
push-to-read plunger to take the reading.