Emerson Rosemount 644, Reference Manual

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75
Reference Manual
00809-0200-4728, Rev RA
Section 5: Operation and Maintenance
April 2015
Operation and Maintenance
Table 5-2. Standard RTD vs. RTD with Matched CVD Constants with Enhanced Transmitter
Accuracy Option P8
Callendar-Van Dusen equation:
The following input variables, included with specially-ordered Rosemount temperature sensors,
are required:
R
t
= R
o
+ R
o
α [t – δ (0.01t-1)(0.01t) – β (0.01t – 1)(0.01t)
3
]
R0 = Resistance at Ice Point
Alpha = Sensor Specific Constant
Beta = Sensor Specific Constant
Delta = Sensor Specific Constant
To input Callendar-Van Dusen constants, perform one the following procedures:
Entering CVD constants using a Field Communicator
From the HOME screen, enter the Fast Key sequence.
Entering CVD constants using AMS Device Manager
1. Right click on the device and select Configure .
2. In the left navigation pane choose Manual Setup and choose the Sensor 1 or Sensor 2
tab depending on the need.
3. Find the Transmitter Sensor Matching (CVD) group box and enter in the required CVD
constants. Or select “Set CVD Coefficients” button to be guided through steps. You
may also select “Show CVD Coefficients” button to see the current coefficients loaded
into the device.
4. Select Apply when complete.
Note
When the transmitter-senor matching is disabled, the transmitter reverts to either user or
factory trim, whichever was used previously. Make certain the transmitter engineering units
default correctly before placing the transmitter into service.
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
644 ±0.10 °C 644 ±0.10 °C
Standard RTD ±1.05 °C Matched RTD ±0.18 °C
Total System
(1)
(1) Calculated using root-summed-squared (RSS) statistical method
±1.05 °C Total System
(1)
±0.21 °C
Device Dashboard Fast Keys
2, 2, 1, 9
TotalSystemAccuracy TransmitterAccuracy
( ) 2
SensorAccuracy
( ) 2
+ =