Emerson 00809-0100-4102 manual Trim the pressure signal, Sensor Trim Overview, Example

Reference Manual	Section 5: Operation and Maintenance
00809-0100-4102, Rev AA	May 2013

Example

A range 4 differential pressure HART transmitter (2051CD4...) will be used in an application with a static line pressure of 1200 psi (83 bar). The transmitter output is ranged with the Lower Range Value at 500 inH20 (1, 2 bar) and the Upper Range Value at 1500 inH20 (3, 7 bar). To correct for systematic error caused by high static line pressure, first use the following formulas to determine the corrected values for the high trim value.

High Trim Value:

HT = (URV - (S/100 x P/1000 x LRV))

Where:	HT =	Corrected High Trim Value
	URV =	Upper Range Value
	S =	Span shift per specification (as a percent of reading)
	P =	Static Line Pressure in psi

In this example:

URV =	1500 inH2O (3.74 bar)
S =	-0.95%
P =	1200 psi
LT =	1500 - (-0.95%/100 x 1200 psi/1000 psi x 1500 inH2O)
LT =	1517.1 inH20

Complete the Upper Sensor Trim procedure as described in “Sensor Trim” on page 68. In the example above, at step 4, apply the nominal pressure value of 1500 inH20. However, enter the calculated correct upper Sensor Trim value of 1517.1 inH20 with a Field Communicator.

Note

The Range Values for the upper and lower range points should be at the nominal URV and LRV. In the example above, the values are 1500 inH20 and 500 inH20 respectively. Confirm the values on the HOME screen of the Field Communicator. Modify, if needed, by following the steps in “Set range points” on page 19.

5.4Trim the pressure signal

5.4.1Sensor Trim Overview

A Sensor Trim corrects the pressure offset and pressure range to match a pressure standard. The Upper Sensor Trim corrects the pressure range and the Lower Sensor Trim (Zero Trim) corrects the pressure offset. An accurate pressure standard is required for full calibration. A zero trim can be performed if the process is vented, or the high and low side pressure are equal (for differential pressure transmitters).

Zero trim is a single-point offset adjustment. It is useful for compensating for mounting position effects and is most effective when performed with the transmitter installed in its final mounting

Operation and maintenance 67