DESCRIPTION AND OPERATION
AUTOMATIC ADJUSTMENTS AND CORRECTIONS
2 - 8
I-E96-301B
®
User Gain and Offset Adjustment
A user-specified linear adjustment may 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 Volt analog input is 0.1 Volts
too high, the slave can compensate for this offset by adding an
offset value of -0.1 for this channel and input type.
User gain value is multiplied times Volts for high level inputs,
times millivolts for low level inputs and thermocouple inputs,
and times 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 function code 217. Once
defined, user gain and offset values remain in NVRAM and are
not lost when module power is interrupted. For more informa-
tion refer to function code 217 in
Engineering Units Conversion
Thermocouple and RTD inputs are converted to the tempera-
ture units specified in function code 216, either degrees C or F.
Conversion 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, 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 conversion to
engineering units (external to function code 215/216 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 slave function code 216 would then output a cor-
rected voltage input reading which may be processed in the
MFP through a square root, polynomial, or other function
block followed by a scaling function to provide the value in
engineering units.
