Calibration; 1Calibration Frequency - Emerson Rosemount Reference Manual

Reference Manual
00809-0100-4021, Rev GC
3.14

Calibration

Calibrating the transmitter increases the precision of the measurement system. The user may
use one or more of a number of trim functions when calibrating. To understand the trim
functions, it is necessary to realize that HART transmitters operate differently from analog
transmitters. An important difference is that smart transmitters are factory-characterized; they
are shipped with a standard sensor curve stored in the transmitter firmware. In operation, the
transmitter uses this information to produce a process variable output, dependent on the sensor
input. The trim functions allow the user to make adjustments to the factory-stored characteriza-
tion curve by digitally altering the transmitter's interpretation of the sensor input.
Calibration of the 3144P may include:




3.14.1 Calibration frequency
Calibration frequency can vary greatly depending on the application, performance
requirements, and process conditions. Use the following procedure to determine calibration
frequency that meets the needs of your application.
1.
2.
a.
b. D/A Accuracy = (% of transmitter span) x (ambient temperature change) °C
c.
d. D/A Effects = (% of span per 1.0 °C) x (ambient temperature change) x (Process
e. Sensor Accuracy = °C
f.
3.

4.

HART® commissioning
Sensor Input Trim: digitally alter the transmitter's interpretation of the input signal
Transmitter-Sensor Matching: generates a special custom curve to match that specific
sensor curve, as derived from the Callendar-Van Dusen constants
Output Trim: calibrates the transmitter to a 4–20 mA reference scale
Scaled Output Trim: calibrates the transmitter to a user-selectable reference scale
Determine the Required Performance
Calculate Total Probable Error
Digital Accuracy = °C
Digital Temp Effects = (°C per 1.0 °C change in ambient temperature) x (ambient
temperature change)
temperature range)
 
TPE = DigitalAccuracy
Calculate Stability per Month
(% per months) x (Process temperature range)
Calculate Calibration Frequency

RequiredPerformance TPE
----------------------------------------------------------------------------------------- -
CalFreq =
StabilityPerMonth
2 2
   
+ D A + DigitalTempEffects

–
Section 3: HART commissioning
2 2
   Effects  
+ D A + SensorAccuracy
April 2014
2
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