Questions on Pneumatic Transmitter and Repeater

Calibrate a pneumatic pressure transmitter to an input range of 0 to 200 inches of water, with an output range of 3 to 15 PSI.

Pneumatic Pressure Transmitter

Suppose you wish to calibrate a pneumatic pressure transmitter to an input range of 0 to 200 inches of water, with an output range of 3 to 15 PSI.

Contents

Complete the following calibration table showing the test pressures to use and the allowable low/high output signals for a calibrated tolerance of +/- 0.5% (of span):

Process Pressure Measurement Tolerance Suppose this transmitter is installed as part of a complete pressure measurement system (transmitter plus remote indicator and associated components), and the entire measurement system has been calibrated within the speciﬁed tolerance (± 0.5%) from beginning to end.

If the operator happens to read a process pressure of 153 inches W.C. at the indicator, how far oﬀ might the actual process pressure be from this indicated value?

Answer

Given the tolerance of ± 0.5% of the 200” span (± 1”), the actual process pressure could be as low as 152 ”W.C. or as high as 154 ”W.C.

pressure transmitter calibration table

Share with us the formula used for the above calculations using the below the comments section.

Pneumatic Pressure Repeater

Examine the diagram for a Foxboro model 139PP pneumatic pressure repeater, then identify multiple faults which could cause this instrument to:

Output less pressure than it should (i.e. less pneumatic signal pressure than process ﬂuid pressure)
Output more pressure than it should (i.e. more pneumatic signal pressure than process ﬂuid pressure)

For each of your identiﬁed faults, explain why the pneumatic output signal pressure will be incorrect, and also identify how to correct the problem.