Hi all, I'm just getting ready to program an application for PID controling the temperature of thermal oil which is heated by 4 banks of heating elements. I have 8 contactors (2 per bank) switching the elements and one thermocouple for the PV. My question is how do I set up the output from the PID loop in the ML1400 as an on/off to one binary output instead of writing this value to an analog output. I have a number of PID applications running analog actuators fairly successfully but up to now none working with this type of setup.
Select a desired time period for time proportioning your outputs. Then use the SCP instruction to scale the PID output to that time period and use that value for your on time.
For example, lets say that you choose one minute. Scale the PID control variable (0-16383) to 60 seconds. Now move that to the preset of a timer for your ON time. A second 60 second timer resets the first.
----------------+-PID-------------+
|PID FILE PD9:0|
|Process Var N7:0|
|Control Var N7:1|
+-----------------+
----------------+-SCP-------------+
|Input N7:1|
|Input Min 0|
|Input Max 16383|
|Scaled Min 0|
|Scaled Max 6000|
|Output T4:0.PRE|
+-----------------|
If you are using solid state contactors then choosing a 16.383 second time proportioning period (if appropriate for your process) and programming the timer with a millisecond time base and the preset word as the PID control variable has the advantage of simplicity.
----------------+-PID----------------+
|PID FILE PD9:0|
|Process Var N7:0|
|Control Var T4:0.PRE|
+--------------------+
