A “smart” DP transmitter with built-in square root characterization is used to measure flow through a pipe.
The orifice plate range is 0 to 150 inches WC at 0 to 480 gallons per minute:
Operations personnel have strong reason to believe that the actual flow rate through this pipe is 160 GPM, yet the DCS registers a flow rate of 182.4 GPM. Based on this information, determine the likely source of calibration error in this system. Also determine whether this transmitter has square-root characterization enabled or not.
Additionally, suggest a good “next step” to perform to either pinpoint the location of this problem or correct it.
The calibration error lies either with the transmitter, the impulse lines (unequal fluid heights inside), or with the orifice plate itself. The transmitter does have square-root characterization enabled.
A good “next step” would be to block and equalize the transmitter manifold to check what its PV and AO parameters register with no applied differential pressure.
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