User`s manual

76 Chapter 7 535 User's Manual
Applications
C. DUPLEX CONTROL
The Duplex control algorithm enables two discrete control outputs for the control
loop. Duplex control is commonly used for applications that require both heating
and cooling or when 2 control elements are needed to achieve the desired result.
Hardware Configuration
• The controller must have two output modules assigned to the loop (any
combination of output modules).
Software Configuration
1. Go to the CONFIG. menu.
Set CTRL.TYPE to DUPLEX.
2. To use different algorithms for each output (PID for the first, and On/Off for
the second):
Go to the CONTROL menu.
Set ALGORITHM to PID:ON/OFF.
3. To make the control action for each output independent of the other:
Go to the CONTROL menu.
Set ACTION:1 or ACTION:2 to either DIRECT or REVERSE action based
on the diagrams in the output examples section (Figures 7.2 through 7.8).
4. Go to the TUNING menu.
Set values for PID OFST:1 (or ON OFST:1) and PID OFST:2 (or ON
OFST:2). These parameters allow the user to independently offset the point
at which output 1 and output 2 become active. PID OFSET units are in per-
cent (%) of control output; ON OFST is in engineering units. The settings
can be used to make sure there is a dead band, i.e., no controller output
around setpoint. They can also be used to overlap output 1 and output 2 so
that both are “on” in a small band around setpoint.
5. Set MAN. RESET (manual reset) term to 50%. This causes the PID output
to be 50% when there is zero error. This term is still active as a “load line”
setting when using automatic reset (integral), so set it to 50% whether using
automatic reset or not.
6. REL. GAIN (relative gain) changes the gain of Output 2 relative to Output
1. Note that the relative gain can limit the maximum output available for
Output 2 when using PID control.
7. Go to the CONTROL menu.
Set LOW OUT. and HIGH OUT. to limit the maximum or minimum outputs
from Output 1 and Output 2. The actual limitation on the outputs is depen-
dent on the offset settings, the relative gain setting and the control action.
Duplex Output State Examples
The following Duplex examples represent a variety of ways this function can
be set up. PID control examples show the PID output percentage on the
horizontal axis, and On/Off control examples show the process variable on the
horizontal axis. The vertical axes are the output of each physical output. Most
of these examples use the first output as heating and the second output as
cooling.
When using PID control, the 535 controller actually displays the PID output.
To relate this output to the actual physical output, locate the PID output on the
NOTE: The duplex output states vary
depending upon:
1. Control Type (PID, On/Off, etc.)
2. Control Action (DA, RA)
3. Output Limits
4. Output Gap or Overlay, and
5. Ouput 2 Relative Gain and PID%
Output.
Please refer to the output state
examples in this section to confirm
that the configuration is appropriate
for the process.
NOTE: Set manual reset/load line
parameters to 50% when using Duplex
control (MAN. RST.:X parameter is in
the TUNING menu.)