ABB 268D/V Operating Instruction page 45

Sensor trimming
If a sensor trimming operation is requested for level transmitters, follow the relevant procedure of the Hand Held Communicator
and PC Software instructions.
If the result is not satisfactory after having carried out either the ZERO TRIMMING or the FULL TRIMMING, the operation must
be repeated with a special variation for these transmitters.
This special procedure dedicated to the level transmitters is as follows:
a) LOW TRIM (low value) for FULL TRIM operation, or ZERO TRIM, only.
A standard operation must be performed according to the procedure. If the result is not satisfactory the operation must be
repeated with a similar procedure but with a new value which has to be entered. This value must be calculated, as follows,
taking in consideration the error with reversed sign:
V
new entered
- 1st Example: Trimming at 10 mbar (applied value)
If the displayed value (via HART) after the first operation, is 10.2 mbar, then the error is +0.2 (10.2 - 10).
The new value to be therefore entered is 9.8 mbar (10 - 0.2).
- 2nd Example: Trimming at true zero (0 mbar)
If the displayed value (via HART) after the first operation, is -0.5 mbar, the operation must be repeated entering + 0.5 mbar.
Note: The LOW TRIM and ZERO TRIM operations affect the span as they do not change the upper
range value previously set. So a high trimming operation according to point b, is highly recommended.
b) HIGH TRIM (high value) for FULL TRIM operation.
A standard operation must be performed according to the procedure. If the result is not satisfactory the operation must be
repeated with a procedure similar to that shown at point a above.
(new calculated value with error taken with reversed sign).
Output % Reranging
Sometimes, in case of tank level measurement, it becomes difficult to calculate the LRV or the URV of the transmitter, or to empty
the tank for zero adjustment. So, not only with flange-mounted, but also with differential pressure transmitters using remote seals,
the Output % Reranging operation helps the user during transmitter calibration.
When it is knows the level of the tank, expressed in percentage, the liquid level, it is possible to input this percentage that
automatically the transmitter recalculates its LRV and URV according to the new percentage value.
This can be done using a HART configuration tool on a 2600T Transmitter.
Two options are available as Output % Reranging operation:
1) OP Range Low
2) OP Range High
As example:
. . . ADDENDUM FOR FLANGE-MOUNTED TRANSMITTERS
V
= applied - (
where both LRV and URV are adjusted
where only URV is change in accordance with the new input percentage
+
V V
displayed - applied)*
Actual level measured by the transmitter:
Transmitter output
Calibration :
a) New input level measurement (Option 1) = 30%
New calibration : LRV
The transmitter output is now = 30%
Starting again from the initial settings:
Transmitter output
Calibration :
b) New input level measurement (Option 2) = 30%
New calibration : LRV
The transmitter output is now = 30%
(*) error
= 27%
LRV = -125 mbar
URV = +340 mbar
= -139.5 mbar
URV = +325.5 mbar
= 27%
LRV = -125 mbar
URV = +340 mbar
= -125 mbar
URV = +291.5 mbar
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