Emerson Rosemount 644h, Reference Manual

Page: 43 / 78

Reference Manual
00809-0100-4728, Rev HA
December 2002
4-3
Models 644H and 644R
4. Set the control loop to manual and select
OK.
5. Select the appropriate sensor trim units at the
ENTER SNSR 1 TRIM
UNITS
prompt.
6. Select 1 Lower Only or 2 Lower and Upper at the
SELECT SENSOR
TRIM POINTS
prompt.
7. Adjust the calibration device to the desired trim value (must be within
the selected sensor limits). If a combined sensor and transmitter
system are being trimmed, expose the sensor to a known
temperature and allow the temperature reading to stabilize. Use a
bath, furnace or isothermal block, measured with a site-standard
thermometer, as the known temperature source.
8. Select
OK
once the temperature stabilizes. The communicator
displays the output value the transmitter associates with the input
value provided by the calibration device.
9. Enter the lower or upper trim point, depending on the selection in
Step 6.
Transmitter-Sensor Matching
Perform the Transmitter Sensor Matching procedure to enhance the
temperature measurement accuracy of the system (see the comparison
below) and if you have a sensor with Callendar-Van Dusen constants. When
ordered from Emerson Process Management, sensors with Callendar-Van
Dusen constants are NIST-traceable.
The Model 644 accepts Callendar-Van Dusen constants from a calibrated
RTD schedule and generates the actual curve to match that specific sensor
curve.
System Accuracy Comparison at 150 °C Using a PT 100 ( α =0.00385)
RTD with a Span of 0 to 200 °C
Standard RTD Matched RTD
Model 644H ±0.15 °C Model 644H ±0.15 °C
Standard RTD ±1.05 °C Matched RTD ±0.18 °C
Total System
(1)
(1) Calculated using root-summed-squared (RSS) statistical method
±1.06 °C Total System
(1)
±0.23 °C
Standard IEC 751
“Ideal” Curve
(1)
Actual Curve
Temperature, °C
R
esist
ance, Oh
m
0 °C
(1) The Actual Curve is identified from the Callendar-Van Dusen equation.
TotalSystemAccuracy TransmitterAccuracy
( )
2
SensorAccuracy
( )
2
+ =