2 - 8 WBPEEUI240774A0
Automatic Adjustments and Corrections
User Gain and Offset Adjustment
A user-specified linear adjustment can be applied to the input
signal before it is converted to engineering units. This gain and
offset is applied to the value obtained after all compensation
and correction operations are performed.
User offset and gain compensates input signals for user correc-
tions. For example, if a 0 to 10 VDC analog input is 0.1 VDC
too high, the ASI module can compensate for this offset by add-
ing an offset value of -0.1 for this channel and input type.
User gain value is multiplied by volts for high level inputs, by
millivolts for low level inputs and thermocouple inputs, and by
ohms for RTD inputs. The default user gain is a value of one.
User offset is added to the input signal. Units of offset are spec-
ified as volts for high level inputs, millivolts for low level inputs,
and ohms for RTD inputs. The default user offset is a value of
zero. Separate user gain and offset values can be specified for
each input channel and each input type. The user gain and off-
set values can be set and reset using FC 217. Once defined,
user gain and offset values remain in nonvolatile memory and
are not lost when module power is interrupted. For more infor-
mation refer to FC 217 in the Composer Function Code Appli-
Composer Function Code Appli-Composer Function Code Appli-
Composer Function Code Appli-
cation Manual
cation Manualcation Manual
cation Manual.
Engineering Units Conversion
Thermocouple and RTD inputs are converted to the tempera-
ture units specified in FC 216, either degrees C or F. Conver-
sion tables representing the voltage (or resistance) to
temperature relationship are used for this conversion. The
table used in performing the conversion depends upon the
input signal type specified.
If the input is identified as either millivolt or high level voltage,
then the specified engineering unit zero and span values are
used to convert the input reading to a scaled engineering unit
value. If special calculations need to be performed prior to con-
version to engineering units (external to FC 215 and FC 216
blocks), then the zero and span values specified in the function
code should be set to represent a standard voltage span for the
input. The I/O module FC 216 would then output a corrected
voltage input reading which may be processed in the controller
To Next Page
Loading...
