123
Reference Manual
00809-0100-4021, Rev GC
Section 3: HART commissioning
April 2014
HART® commissioning
Figure 3-11. Trim
3.15.1 Sensor input trim
The Sensor Trim command allows for alteration of the transmitter’s interpretation of the input
signal as shown in Figure 3-11 on page 123. The sensor trim command trims, in engineering (°F,
°C, °R, K) or raw (, mV) units, the combined sensor and transmitter system to a site standard
using a known temperature source. Sensor trim is suitable for validation procedures or for
applications that require profiling the sensor and transmitter together.
Perform a sensor trim if the transmitter’s digital value for the primary variable does not match
the plant’s standard calibration equipment. The sensor trim function calibrates the sensor to
the transmitter in temperature units or raw units. Unless the site-standard input source is
NIST-traceable, the trim functions will not maintain the NIST-traceability of your system.
The trim functions should not be confused with the rerange functions. Although the rerange
command matches a sensor input to a 4–20 mA output—as in conventional calibration—it does
not affect the transmitter’s interpretation of the input.
Note
A warning will appear “Set the Control Loop to Manual” (see “Setting the loop to manual” on
page 10.)
Application: Linear Offset Application: Linear Offset and
Slope Correction
Solution: Single-Point Trim Solution: Two-Point Trim
Method:
1.Connect sensor to transmitter. Place sensor in
bath between range points.
2.Enter known bath temperature using the Field
Communicator.
Method:
1.Connect sensor to transmitter. Place sensor in
bath at low range point.
2.Enter known bath temperature using the Field
Communicator.
3.Repeat at high range point.
One-Point Trim Two-Point Trim
Transmitter System Curve
Site-Standard Curve
HART 5 Fast Keys
3, 4, 4
HART 7 Fast Keys
3, 4, 4
Resistance (ohms)
Temperature
Resistance (ohms)
Temperature
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