Installation manual

Publication 1747-RM001G-EN-P - November 2008
9-28 Proportional Integral Derivative Instruction
For example, if measuring a full scale temperature range of
-270°C (PV=0) to +1000°C (PV=16383), enter a value of -270 for Smin
and 1000 for Smax. Remember that inputs to the PID instruction must
be 0 to 16383. Signal conversions could be as follows:
2. Enter the setpoint (word 2) and deadband (word 9) in the same scaled
engineering units. Read the scaled process variable and scaled error in
these units as well. The control output percentage (word 16) is displayed
as a percentage of the 0 to 16383 CV range. The actual value transferred
to the CV output is always between 0 and 16383.
When you select scaling, the instruction scales the setpoint, deadband, process
variable, and error. You must consider the effect on all these variables when
you change scaling.
Output Alarms
You may set an output alarm on the control output (CO) at a selected value
above and/or below a selected output percent. When the instruction detects
that the output (CO) has exceeded either value, it sets an alarm bit (bit 10 for
lower limit, bit 9 for upper limit) in word 0 of the PID control block. Alarm
bits are reset by the instruction when the output (CO) comes back inside the
limits. The instruction does not prevent the output (CO) from exceeding the
alarm values unless you select output limiting.
Select upper and lower output alarms by entering a value for the upper alarm
(word 11) and lower alarm (word 12). Alarm values are specified as a
percentage of the output. If you do not want alarms, enter zero and 100%
respectively for lower and upper alarm values and ignore the alarm bits.
Table 9.41 Signal Conversions
Parameter Range
Process limits − 270 to + 1000 °C
Transmitter output (if used) + 4 to + 20 mA
Output of analog input module 0 to 16383
PID instruction, Smin to Smax − 270 to + 1000 °C