problem with PID control

Hello i am new here and have a question regarding pid control loops.

I am currently working on a project for my company which uses a unitronics vision 280 with E2B and 2 expansion modules for analog in and out. The project involves a liquid helium heater which has a temperature sensor on it. The temperature sensor is first directed to a shinko unit which uses a setpoint. The output signal from the shinko is then directed to the analog input module. On the plc it must be possible to change the setpoint and minimum and maximum temperature limits. This is done using MI. But when the system is running the pid loop does not work. I did read about pid loops and studied the example from unitronics but it does not work.
A picture of the settings i use on pid are shown below. What i see is that the control value stays the same and the output does not change.
Furthermore i also see that the heater is using the setpoint of the shinko instead of the setpoint from the plc. Meaning that a change in the shinko SP would also change the heater proces.

My question is if these settings are correct or if something is missing here. I also want to know if someone uses shinko's between a sensor and a plc and what his experience was.

You show the configuration but do you have any logic to turn on the PID function? Also, is the PID output writing to the analog output?

The temperature sensor is first directed to a shinko unit which uses a setpoint. The output signal from the shinko is then directed to the analog input module.

Click to expand...

If the Shinko uses a setpoint, it must be a controller, not a transmitter (transmitters don't have setpoints). Therefore the Shinko output is the output of the PID algorithm in the Shinko controller, it is not a retransmission of the temperature. Correct? Have I missed something?

What the PLC is receiving is not the process variable (PV), the temperature, rather it's receiving the PID output of the Shinko controller.

I don't understand why you would want to send the PID output to the PLC.

If you want to run PID on the PLC, you'll have to get the temperature signal into the PLC as the process variable, compare it to a setpoint and uses the output of the PLC controller to drive the heater.

Dan

Not familiar with the Shinko unit, but other temperature controllers/conditioners such as Omega can be repeaters. They convert an RTD or thermocouple signal to 4-20 and provide a local readout. So...the Shinko may or may not be a controller. It could be a converter. The setpoint is for local alarming, the text changes colors etc...
Some also have aux. contacts for alarms.

Hard to say with the information provided, but this could also be part of a cascade control scheme.

Ken

Thanks for replying everyone

Here is the additional information:

The shinko can be set as a controller. If this is done it uses a PID loop. However it is setted as a converter meaning that it converts the signal from the teperature sensor. The converted signal is then send as a 4-20mA signal to the analog module. From there the signal goes to the plc. This signal comes in but the PID loop does not activate on it. There is a signal originating from the analog output to a eurotherm (temperature regulator) which controls the temperature of the helium heater. But the PID loop does not work so this signal is the same signal strength in mA all the time.

The PV is reading internal memory address (M1) 22. Is the physical input copied into this address?

Is the sequence below correct?

temp sensor --> Shinko re-transmitter 4-20mA output --> PLC AI --> PLC PID ---> PLC 4-20mA AO --> Eurotherm ? ?

What function does the Eurotherm do? Is it a controller or an SCR power unit? what does it connect to? What model number is it?

Dan