PID Tuning - HELP!

[onelegout]

Yeah I canceled autotune, I'm really starting to wonder about my sensors and PID.
I've got another one which seems to do the same thing though! I'll try swapping them next week.
I've put in your PID values, and the temp seems to be read much more often now, but the output light seems to flash as if it's switching on and off every second or less - before it was either on or off, I hope this doesn't fry my SSRs!

I've reset the temp correction to the correct value to try and see if that makes a difference.

It's just going to be a case of waiting and trying different things I think!

 

[Walker]

I've put in your PID values, and the temp seems to be read much more often now, but the output light seems to flash as if it's switching on and off every second or less - before it was either on or off, I hope this doesn't fry my SSRs!

Son't worry about those SSRs. Rapid on/off switching is the whole reason we use SSRs. They are just large chunks of silicon and won't wear out due to the switching.

 

[onelegout]

Ok I've decided to make a decision here and buy new PIDs and sensors. It's very hard to find good PT100 sensors here in the UK, do you have any reccomendations on which to use? I'd really like to make a PT100 switch box as well, so I could switch between inputs for different functions (sensor in HLT for heating HLT water, switchable with sensor in Heat exchanger output for herms use.) but I don't know much about that kind of thing. I know that thermocouples require special wire and that you can't just wire them up to a switch, but is the same true for RTDs?

P.S. which PID should I get? The auber one?

 

[Walker]

I did not buy the Auber PID. I only used the image as a reference.

I bought my PID off ebay. It's a "TET612" and shipped from China.

Are you sure the PID and sensors are bad, though?



As for the RTD's. They use more than 2 wires with the point of that being that the PID can compensate for resistance added by things like long wires or connectors or switches.

You should be able to use a selector on RTDs with out any issues, but this is me just repeating what I have read. I have not actually done this myself.

 

[onelegout]

I did not buy the Auber PID. I only used the image as a reference.

I bought my PID off ebay. It's a "TET612" and shipped from China.

Are you sure the PID and sensors are bad, though?



As for the RTD's. They use more than 2 wires with the point of that being that the PID can compensate for resistance added by things like long wires or connectors or switches.

You should be able to use a selector on RTDs with out any issues, but this is me just repeating what I have read. I have not actually done this myself.

I'm pretty sure that its a bad sensor or some other problem - I'm going to try and get some good PT100 probes anyway, and if that doesn't help things at least I'll have some better quality sensors

 

[onelegout]

Ok, today I took the control box indoors and did some tests. I had diagnosed the problem as a faulty sensor, or faulty PID. I decided to test the sensors' accuracy with an ice bath, tepid water bath, and boiling water.

I had three types of sensor, pt100 sensors from virtual village, K type thermocouples from virtual village, and J type thermocouples from ebay.

The PT100 sensors did not work at all, giving me an error in every configuration.

The J type thermocouple I had been using in my tests at the beginning of this thread would only read up to 67*c.

The K type thermocouple would only read up to 45*c

I had 3 J type thermocouples, so tried one of the others that I had not used, and hey presto it works perfectly! Senses the temperature accurately and correctly all the way up to boiling point. I'm now going to fix a couple of leaks on the brewery and run another autotune test with the new sensor.

 

[Walker]

my first probe was a pt100 from virtual village. The probe worked fine for me, but the cable connected to the thing wasn't very sturdy and developed a loose connection after a while.

When you had your pt100's connected, did you change the setting on the PID to tell it that you were connecting a pt100?

 

[onelegout]

My PIDs are supposed to be able to determine what type of sensor it is automatically, but I'm sure they don't do it correctly.
I'm going to run the autotune test now, but I'm doing it from cold without bringing the temps up to around 60*c first. Is this the right thing to do or should I get it to temp first?
H

 

[Walker]

My PIDs are supposed to be able to determine what type of sensor it is automatically, but I'm sure they don't do it correctly.

Oh, wow. I've never seen that before.

I'm going to run the autotune test now, but I'm doing it from cold without bringing the temps up to around 60*c first. Is this the right thing to do or should I get it to temp first?
H

What I saw suggested (and what I did myself) was turn the PID on and let it start heating the water up by itself. Once it got near the set temp, then flip it into auto-tune mode and wait.

 

[onelegout]

ok cool well what I'm going to do is test it autotuning from cold, and see how it goes, then if it doesn't work as I'd have liked I can give it another go tomorrow. I fixed a few leaks too today, so even if this doesn't work at least I've done something productive!

25 mins into the autotune so far, and it seems to be going about right. The only anomaly I've seen is that my current reading of the BK(MT) is a degree higher than the output of the hex, which is odd!

 

[Walker]

The only anomaly I've seen is that my current reading of the BK(MT) is a degree higher than the output of the hex, which is odd!

Did you calibrate all of the sensors and enter any temp offsets into the PIDs?

Your might just have one sensor that is reading a little off.

My first probe had a static error of 3.5*F. The new one has a static error of 1.5*F. If I were to use those with out accounting for the errors, I would see temp differences 2.0*F between the two probes.

 

[onelegout]

I'm using one sensor attached to the hex output on the PID and sensing the other temps using a calibrated digital thermometer.
I'm running a new test with the set point at 45*c so that I can test the PID's ability to hold a temperature and complete an autotune session. We'll see how that goes!

I've set the correction to make the sensor correct using an ice bath and boiling water to get it right and checking it at different temperatures with my digital thermometer, but I think my homemade thermowell in the HEX output takes a while to adjust to the correct temperature, so part of the reason I'm testing the brewery at the mo is to see what the correction should be. Right now it looks like the sensor inside the thermowell is around 3*c colder than the liquid in the hex.

 

[Walker]

Ah.... I didn't realize you were using a thermowell.

I put a DIY thermowell in my MLT (for a small probe thermometer) and that thing always reads about 1*F lower than the actual temp inside the MLT (as measured with the same thermometer), so that might have something to do with it.

 

[onelegout]

yeah I think mine takes a minute or two to catch up; I'll calibrate it as soon as I can get hold of a new thermometer - mine decided to die today half way through the test!
The PID seemed to work ok but I think I may have to tune it myself manually. I've been looking into PID tuning and have a basic idea on how to do it. The main focus for now is making sure that the PID reads the correct temperature, as I still have not got confidence in the accuracy of the sensor.

Tomorrow my goal is to calibrate the sensor with the thermowell.

 

[onelegout]

Ok a quick update on this

I've been very suspicious about the PID's I had. They were bought from ebay and were from Italy. The manuals I had for them were all in Italian, and when they sent me an English one I realised it was for a slightly different model. I finally got one of the PIDs working properly with a sensor but when I ran a brew test on it with water, it didn't track the temperature properly, and kept getting stuck at certain temperatures for ages.

I eventually got really annoyed and posted a rant on facebook about how I was fed up with temperature control systems, to which a friend said 'you know I work for a PID company right?'

So I'm now the proud owner of two new PID controllers They're West Control Systems '6100+' and '6700+' models, and will hopefully do a much better job than the italian ones did

I'm going to set them up and try them out in a bit, will have some inital results by this evening.
H

 

[BrewBeemer]

So I'm now the proud owner of two new PID controllers They're West Control Systems '6100+' and '6700+' models, H

This is what I come up with using a different address for that PID if this helps;
http://iseinc.com/process_and_temperature_controls.htm

 

[onelegout]

I finally sorted the new PID controller - had to use a battery pack circuit to use the relay output of the PID to switch an SSR (the PID had no SSR driver).

My first test of the new PID was odd - the temp kept rising and the output wouldn't turn off - then I realised something! There are two modes, 'direct' and 'reverse' acting. I had assumed that the 'direct' mode was for heating and the 'reverse' mode was for cooling - its the other way around!

 

[Walker]

I finally sorted the new PID controller - had to use a battery pack circuit to use the relay output of the PID to switch an SSR (the PID had no SSR driver).

Ouch. Mechanical relays will wear out over time. If you ever have to replace it, look around for one that can drive an SSR directly.

My first test of the new PID was odd - the temp kept rising and the output wouldn't turn off - then I realised something! There are two modes, 'direct' and 'reverse' acting. I had assumed that the 'direct' mode was for heating and the 'reverse' mode was for cooling - its the other way around!

Hmmmm... If the PID was set to act as a "cooling" device, wouldn't that mean that the heat would not have even been turned on at the start of te test (when the measured temp was already lower than your set temp)?

 

[onelegout]

I used the manual mode to ramp the temperature - and it appears that I now have it working!!!

The temp had risen to 75*c, I set the mode to 'reverse acting', and the output turned off. It dropped to 65.9, the output turned on. It rose to 66.1, the output turned off!

It's held 66*c within 0.5 degrees now for 20 minutes, and occilates by 0.2*c every minute or so. Fingers crossed it will stay like it

Oh, and I'm trying to get my hands on an ssr driver board for my PID, as the company does make them and they're a simple switch.

 

[onelegout]

SUCCESS! We finally have fully functional PID control!

it's been within 0.2 degrees of 66*c for half an hour, apart from once when I had to turn off the pump for 30 seconds to fix a leak, when it dropped to 59.5*c

The problem I have with measuring it now is that it oscillates quicker than I have been measuring it. I'm now going to sit with it for 15 mins and record the temp every 30 seconds or so.

 

[cdbrown]

Reverse mode is the one you want to let the PID do the work. When doing autotune it's best to be at the temp you normally want before running it so let the system run for a while and then hit the autotune setting. Run the autotune for a couple of batches and then let it do it's job. It's great to be able to walk away and come back an hour later to see it ramping up to mash out temps.

 

[onelegout]

I'm not sure auotuning further is even necessary as I measured the oscillations and it doesn't deviate by more than 0.3*c, which I thing is more than good enough for brewing I'm going to clean the whole thing out and get brewing on it asap will be great to see how it does with a proper mash nit just water