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4.14 Scale Adjustment Page
Information.
•
Process variable, Remote set point and position feedback inputs do not require
recalibrating when the input type or range is changed.
•
Scale Adjustment Reset – removes any previously programmed offset or scale
adjustment settings.
•
System offset errors – can be removed using Offset Adjustment.
•
System scale errors – can be removed using Span Adjustment.
•
Offset/Span Adjustment – can be used to perform spot calibration.
Switch off the power supply. Connect accurate signal sources, suitable for simulation over the
entire input ranges, in place of the process variable signal connections (terminals 10, 11, 12),
remote set point signal connections (terminals 7, 8 and 9) and position feedback connections
(terminals 4, 5 and 6). For thermocouple inputs, connect the millivolt source using appropriate
compensating cable – see Section 4.6.1 of the Installation Guide . For 2-lead resistance
thermometers the resistance box may be connected at the sensor end of the leads or the lead
resistance must be added to the calibration values.
As a general rule, spot calibration values should be:
< 50% of range span value when using Offset Adjustment parameters.
> 50% of range span value when using Span Adjustment parameters.
SCALE
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Page header – Scale Adjustment
Process Variable Scale Adjustment Reset
Set
no
and span values to their nominal values.
displayed to indicate that these parameters have been
reset.
Process Variable Offset Adjustment
––––
Electrical and resistance thermometer inputs
Apply the correct input for the spot calibration required.
For RTD inputs, use resistance values obtained from
standard tables.
Thermocouple Inputs
Measure the ambient temperature at the output terminals
of the signal source (calibrator). From thermocouple tables
obtain the millivolt equivalent of this temperature (a) and
that for the spot calibration temperature (b). Subtract (a)
from (b) and set the signal source to the resultant value.
(The voltage is negative if the spot calibration temperature
is below the measured ambient temperature).
Note. The displayed units are engineering units.
Set the value required. The decimal point position is set
automatically.
Example – If the display range is 50 to 250.0 and a spot
calibration is required at 100.0 and 225, inject a signal
equivalent to 100 and set the display to 100.0.
Continued on next page.
and press
to reset the process variable offset
YES
:
4 CONFIGURATION...
dONE
:
is
45
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