PT_COMP composite template

The PT_COMP composite template is used to compensate a measured flow based on measured pressure and/or temperature. The compensation can be used for gas or liquid streams where flow is measured using either a differential pressure flowmeter or a mass flowmeter. Flow compensation of a gas stream can be based on measured pressure, temperature or both. Compensation for liquid flow is based on measured temperature, using a linear relationship between temperature and density.

Inputs to the block are the measured flow, pressure, and temperature. The block output is the compensated flow. The status of the compensated flow is that of the measured flow. If the status of the measured pressure or temperature is other than Good, the reference (calibration) value is used in the calculation when applicable. This effectively disables compensation based on that input when the status is not Good. Status transitions are bumpless in downstream control blocks.

Note

All (gas and liquid) compensated flows are limited between 90 and 110% of the uncompensated flows. Use the COMP_LO_LIM and COMP_HI_LIM parameters to change these limits.

The compensation factor is calculated as follows:

Gas Stream

(( PRESSURE + ABS_PRESS_CF ) / ( REF_PRESS + ABS_PRESS_CF ))
*
(( REF_TEMP + ABS_TEMP_CF ) / ( TEMPERATURE + ABS_TEMP_CF ))

Liquid Stream

(( TEMPERATURE * DENSITY_M ) + DENSITY_B ) / REF_DENSITY

If the flowmeter is the differential pressure type, the compensation factor is the square root of the above equations.

You create a usage of this composite template by placing a custom block on the module's function block diagram. From the Special Items palette in Control Studio, drag the Custom Block icon onto the diagram. Give the block a usage name and select the block type as Linked Composite. Reference the existing object by browsing to the PT_COMP template.

This block can be configured using Control Studio or DeltaV Explorer, as well as from the faceplate in DeltaV Operate or DeltaV Live (provided the user has the Restricted Control security key). To configure this composite function block for DeltaV Operate, use the PT_COMP_ dynamo (in the frsFncblk dynamo set). To configure this block for DeltaV Live, use the PT_COMP_ GEM class (in the Function Block GEM class folder).