Tuning industrial PID controller module for water chiller? - Page 1
Forum section: electronics / beginners

author: LinuxHata
author_rank: Frequent Contributor
timestamp: June 26, 2023, 12:07:06 pm
content: Hello.I have a common REX C100 type PID controller with relay output.I've used them countless times for heating applications and they do work fine.However, when I need to use it with water chiller (for K40 laser), it does not work as needed.I've configured it for cooling from the menu, according to the manual, and it do works, but it tries to cool down like it does for heating - by giving short, 3-4 second pulses to chiller compressor. Of course, this approach does not work with water as it should. I tried to launch auto-tuning, it took several hours but returned with error.So is there a way to adjust it in a simpler way? Like this:Turn output on, if water temperature is above X value.Turn output off, if water temperature is below Y value.So I basically need to disable PID control ?Here's manual for it:https://www.rkcinst.co.jp/english/downloads/8933/imnzc22e1/

author: Jeroen3
author_rank: Super Contributor
timestamp: June 26, 2023, 12:21:25 pm
content: For compressors you need to configure a minimum on time, and it takes some time for it work, and there is a maximum number of switch-ons per hour.Looks like you can set a "Cool-side proportioning cycle" can you set that to minutes?

author: LinuxHata
author_rank: Frequent Contributor
timestamp: June 26, 2023, 01:09:56 pm
content: The manual is very weird, looks like google-translated from chinese.It is currently set to 20, can be set from 1 to 100.

author: jbryan189
author_rank: Contributor
timestamp: June 26, 2023, 01:35:11 pm
content: Looking at the iffy manual, I can assume the SL2 parameter is set to [0011 F Water cooling (W type)]? Thats pretty nice parameter but not exactly sure how it will effect the PID loop?Let us know as this is interesting for me anyways.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: June 26, 2023, 02:43:12 pm
content: Yes I have set it to water cooling.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: June 27, 2023, 12:43:59 am
content: For cooling applications like that you typically have circulating chilled water and control the cooling cycle with a control valve on the chilled water, not by turning the compressor on and off.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 27, 2023, 07:44:23 am
content: As others have said, you can't turn the compressor on/off quickly enough. On the other hand, well stirred/mixed water based system does not need PID control, simple hysteretic is probably good enough (unless you need some 0.1degC accuracy).The simplest you can do is to increase the reservoir volume of water so that temperature change during compressor on (cooling) or compressor off (heating by the load) is slower. Then you can use simple on/off thermostat and the duty cycle will be long enough (like 10 minutes for a compressor), and the water temperature does not change too much during that period.Adding a controlled mixing valve allows faster control. Then you would set the water reservoid temperature to something like 5degC colder than needed, and it could be allowed to oscillate as long as it's always at the minimum required temperature or lower. Then use a motorized 3-way mixing valve to distribute that water into the system, mixing some returning water to bring the temperature up. Driving that valve would need a PID loop or something.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: June 27, 2023, 11:09:43 am
content: I had simple, selfmade system, which was using DS18B20 as sensor and some PIC to control the relay and everything was fine so far. But it got immersed in water and went away. So, as an alternative, I decided to use existing PID controller, but switch PID mode off. I almost achieved it - by changing a lot of values which was set at max, to min, which was set to min, set to maxnow it works, just for some times, it tries for half second to turn off the output, but compressor does not notice that at all.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 27, 2023, 02:26:18 pm
content: Well, according to the manual you posted, C100 is not available in W control variant (first letter after C100 family part number) at all. Clearly the product is unsuitable for the job. Probably easiest is to replicate your working PIC-based controller which will easily allow modifications like minimum on-time and minimum off-time in software.