ABB 691HT Operating Instructions Manual page 41

LRV : - 200
URV : + 200
OP : [ 50 ] %
< - - - - > CLR
PV : 0.01 mbar
OP : 45 %
O/P O/P
LOW HIGH
LRV : - 180
URV : + 220
OP : [ 45 ] %
< - - - - > CLR
PV : 0.01 mbar
OP : 60.00 %
O/P O/P
LOW HIGH
WARNING - Loop may
be returned to Auto
C A L I B R A T I O N
PV OUT RERAN
SCALE % GING
Use of the Green Keys - TRIM - Sensor Trimming option ( for KST temperature transmitters )
The Sensor Trimming operations in the temperature
transmitters is to correct the characterisation parameters
stored in the transmitter's EEPROM during the last cha-
racterisation process, either the first, factory done, or a
subsequent trimming operation, in order to match your
standard calibration equipment.
To understand completely the reason for this operation it
is necessary to know that during the manufacturing the
transmitter's digital output is compared to different input
in order to obtain parameters that are stored in the
EEPROM: these parameters, applied to a suitable
algorithm, provide a precise primary output linearisation.
During the use of the transmitter the sensor is submitted
to various influences, mainly ageing, that can affect the
original characteristics.
The effect of these changes is that, although through the
reranging operation the analog output matches with the
input signal, the interpretation of this signal by the tran-
smitter is incorrect and the Process Value indication, in
engineering units, doesn't match with the real input.
The sensor trimming operation forces two points, usual-
ly the zero and full scale values, to match exactly the
primary output: these values are stored in the transmitter
in a permanent way.
The K-ST Smart Temperature Transmitter is able to store
in its EEPROM two different set of parameters, related to
the Factory Trim and the User Trim.
While the first one recalculates the LRV and URV maintaining the original
SPAN, the O/P HIGH recalculates the URV so the SPAN can be
changed.
When F1 (O/P LOW) is pressed the existing LRV and URV are displayed,
ENTR
and the user is asked to input the evaluated output in percentage, while
between square brackets it is given the actual one.
Press F4 (ENTER) to accept the new percentage.
The "wait . . . . " message is given till the operation is completed, and so
the new output percentage is displayed.
LRV and URV have been changed, according to the new output
percentage.
ENTR When F2 (O/P HIGH) is used, again the LRV and the URV are displayed.
By setting the new output percentage and pressing F4 (ENTER) a new
URV is calculated according to the new output percentage.
If the new setting has been performed correctly, the new output percentage
is displayed, together with the PV indication.
Use ESCAPE to exit and to return to the CALIBRATION menu.
PRO
CEED
After the warning message: "Loop may be returned to auto" press F4
(PROCEED) to return to the CALIBRATION MENU.
Additional information and examples on the use of PV Scale and Output
% reranging are given in the 600T EN Series Instruction manual.
The Factory trim parameters are obtained during the
manufacturing process and are not modifiable by the user,
while the User trim parameters can be set by the user
using his standard calibration equipment.
The user trim parameters are set by default, unless a
custom calibration is required, to the same values than the
factory trim parameters. If the transmitter has been custom
calibrated the user trim parameters are set accordingly to
the custom calibration.
The sensor trimming operation should be done using
testing equipment, millivolt generator or ohms reference,
of a suitable class ( accuracy at least three times of the
transmitter accuracy ). If such equipment is not available,
the Factory trim parameter can be satisfactorily used in
most of the cases.
For millivolt or thermocouple sensor type connect your
millivolt source accross the terminals 2 (+) and 1 (-). If
the transmitter is set for differential measurement short the
terminal 2 and 3. All the connection should be done
using copper wires.
For ohm or RTD sensor type connect your ohms referen-
ce accross the terminals 1 and 4. If the transmitter is set for
a three wires measurement short the terminal 1 and 2,
while if it is set for four wires measurement the terminals
3 and 4 should be shorted as well. For ohm or RTD
differential measurement connect your ohms reference
accross the terminal 1 and 4 and insert accross the
terminal 1 and 5 a resistor having a value included
between the low and the high trimming value.
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