Emerson Rosemount 644 with HART Protocol, Reference Manual

Page: 77 / 112

69
Reference Manual
00809-0200-4728, Rev SA
Troubleshooting
July 2018
Troubleshooting
Figure 5-3. Recalling the Sensor Trim with the LOI
5.4.4 Active calibrator and EMF compensation
The transmitter operates with a pulsating sensor current to allow EMF compensation and detection of
open sensor conditions. Because some calibration equipment requires a steady sensor current to
function properly, the “Active Calibrator Mode” feature should be used when an Active Calibrator is
connected. Enabling this mode temporarily sets the transmitter to provide steady sensor current unless
two sensor inputs are configured.
Disable this mode before putting the transmitter back into the process to set the transmitter back to
pulsating current. “Active Calibrator Mode” is volatile and will automatically be disabled when a master
reset is performed (through HART) or when the power is cycled.
EMF compensation allows the transmitter to provide sensor measurements that are unaffected by
unwanted voltages, typically due to thermal EMFs in the equipment connected to the transmitter, or by
some types of calibration equipment. If this equipment also requires steady sensor current, the
transmitter must be set to “Active Calibrator Mode.” However, the steady current does not allow the
transmitter to perform EMF compensation and as a result, a difference in readings between the Active
Calibrator and actual sensor may exist.
If a reading difference is experienced and is greater than the plant’s accuracy specification allows,
perform a sensor trim with “Active Calibrator Mode” disabled. In this case, an active calibrator capable of
tolerating pulsating sensor current must be used or the actual sensors must be connected to the
transmitter. When the Field Communicator, AMS Device Manager, or the LOI asks if an Active Calibrator
is being used when the sensor trim routine is entered, select
No to leave the “Active Calibrator Mode”
disabled.
5.5 Trim the analog output
5.5.1 Analog output trim or scaled analog output trim
Perform an output trim or a scaled output trim if the digital value for the primary variable matches the
plant’s standards but the transmitter’s analog output does not match the reading on the output device.
The output trim function calibrates the transmitter to a 4–20 mA reference scale; the scaled output trim
function calibrates to a user-selectable reference scale. To determine the need for an output trim or a
scaled output trim, perform a loop test (
“Performing a loop test” on page 30 ).
CALIBRAT CALIBRAT
DAMPING
VARIABLE MAP
TAG
ALM SAT VALUES
PASSWORD
....
VIEW CONFIG
SENSOR CONFIG
UNITS
RERANGE
LOOP TEST
DISPLAY
EXTENDED MENU EXTENDED MENU
EXIT MENU
SENSOR 1 CALIB
SENSOR 2 CALIB*
ANALOG TRIM
FACTORY RECALL FACTORY RECALL
BACK TO MENU
EXIT MENU
....