Omron CP1E with TS101 expansion temperature control

[sehonn]

Hello,

I am trying to write a program for a freezer system. I have a CP1E with TS101 expansion for testing, but the actual project will use another CPU, not sure yet which one.

I have to control the temperature in 15 cooling warehouses with a single PLC. The warehouses are using shared ammonia compressors to obtain cold air. The temperature has to be precisely -22 degrees Celsius in each warehouses(+,- 0,5 degrees C). When the temperature goes above -21 degrees for more than 2 mins in one of the warehouses, the ammonia compressors start to work and a valve brings the cold air to the warehouse. When the temperature reached -22 degrees, the walve closes, and the compressors stop to work (unless they are needed to cool down another warehouse.) There will be a PT100 in each room

Since the temperature has to be very precise, I assume that I have to use PID control

I have never made any temperature or PID control before, so I need some light from you guys

I read the manual, but I need some more explanation to understand it.

If you could show me a sample program of a PID temperature control with some explanation, I would be very thankful .

 

[gclshortt]

Information on PID:
http://blog.opticontrols.com/archives/344
https://www.csimn.com/CSI_pages/PIDforDummies.html
http://www.plctalk.net/qanda/showthread.php?t=25338
Videos:
https://www.youtube.com/watch?v=0vqWyramGy8
https://www.youtube.com/watch?v=wbmEUi2p-nA

I would tackle the problem using individual process temperature controllers that will communicate back to a central PLC for local control and monitoring.
Example:
https://www.automationdirect.com/adc/Shopping/Catalog/Process_Control_-a-_Measurement/Temperature_-z-_Process_Controllers
Solo process temperature controllers have Modbus RTU (RS485) communication built into the unit and start at a price of $90 USD each.

The Omron CP1 controllers have modbus adapters for the communication.
https://www.myomron.com/index.php?action=kb&article=1243

Using temperature process devices will allow individual control at the cooling location and have remote control in a central location (PLC).

Hope this helps you out.
Regards,

 

[gtsuport]

For the actual project, I would suggest looking at a CJ2 processor and CJ1W-TCxxx modules.

As the gclshortt has suggested individual loop controllers may be a good way to control this system.

The CJ1W-TCxxx modules are basically loop controllers integrated into a plc module. There are 2 loop and 4 loop modules. Autotuning of loops is supported on the module.

Just my $0.02.

 

[sehonn]

Thank you for your answer, although I am familiar with the prinicples of the PID controllers.

Unfortunatelly I cannot use individual process temperature controllers, I have to solve the problem without them.

In the meantime I got the information of the CPU and expansion type.

CPU: CJ2M-CPU33

Expansion: CJ1W-TS562

Probably the first time I am going to lay my hands on the actual CPU, is going to be the time when I have to upload the program to the system. So first I would like to test a single temperature PID control on my CP1E to see if it works.

 

[danw]

What device can you modulate with PID? A flow valve to an evaporator? A damper?

PID is used to modulate, as opposed to on-off control. Devices that switch on-off, like a solenoid valve is controlled in "time proportioning mode", where the device is On for some fraction of a fixed time interval and OFF for the remainder of the time interval. The Calculated PID output, 0-100%, is the percentage of ON time. This means that even when the temperature is 0.1 deg off setpoint, the will still "call for" cooling, although with a very short ON period.

Years ago, chiller compressors were run on-off. Maybe there've been changes in technology to where compresors can tolerate or survive frequent cycling. Years ago refrigeration was designed for optimal efficiency at fixed compressor motor speed. Maybe technology has changed.

 

[gtsuport]

Sehonn,
The CJ1W-TSxxx module is a temperature sensor module, you would need to create the PID code in your program.

The CJ1W-TCxxx is a temperature control module and handles all that for you.

Download the W483 manual for the CP1E.
This will provide all the information on the CP1E instructions including PID.

 

[gtsuport]

Sehonn,
Just re-read your original post.
Tried to locate some example code.
Located a tutorial on myomron.com, but it is not in English.
Myomron.com is a European Omron support website.
You could register there and review the information.

I don't typically work with PLC PID, so don't have any examples.
Usually the biggest issue is getting the term values in the correct units. Also make sure you allocate enough D memory for the Control area of the instruction.

 

[sehonn]

Hey guys,

I have just visited the plant where I had the chance to check other freezer systems. The reason why they suggested to use CJ2M-CPU33 and CJ1W-TS562 is that all the other freezers use them and non of them have PID control.

It means that I also don't have to make it. I have other questions though, but I just make another topic for them since they are not related.

Thanks!