Home Brew Forums > Problem with PID PV reading

09-30-2012, 02:16 PM   #1
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I've been getting some weird readings from my rex c100s.

I'll set the 'set value' to 66, it will heat the water up to that level and then the 'present value' display will read as if it is holding a steady temp at 66.

Afterwards I'll raise the set value to 75, and instantly the present value temperature reading will increase dramatically.

I have no idea what is going on here. Do any of you know what it could be? I have some video of this happening in my later posts.

Here are a couple pics of my set up:

Note: I hadn't calibrated the temperatures yet in this picture, so that's why the PVs for the three PIDs are all reading different room temperatures. And, yes, I know the middle one isn't currently connected to an SSR.

09-30-2012, 03:04 PM   #2
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I believe that the actual temperature of the water is somewhere close to 43 degrees C, but the reading fluctuates when I change the set value.

You can see the changes in readings in this video.

Between 10-30°, I'm getting a consistent PV reading.
10.3° SV = 42.9° PV
20.3° SV = 42.9° PV
30.3° SV = 42.9° PV

When I hit 40° (close to the actual temperature, but a little under) the PV reading drops 2° .
40.3° SV = 40.9 PV

If I set the SV over the real reading, it goes back to reading the normal PV.
50.5° SV = 42.9 PV

Lastly, I demonstrate that the reading gets more and more off the closer I get to the real temperature reading.
33.3° SV = 42.8 PV
35.3° SV = 42.4 PV
37.3° SV = 41.9 PV
39.3° SV = 41.5 PV

09-30-2012, 06:09 PM   #3
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I went back and turned the auto-tune back on and started over, but I'm still having problems.

In this video, I set the set value to 51.5 and let it heat up to that temp. After that, the present value reads 51.5 for a long time. Then, once I change the SV, the PV jumps up 52.2 and continues to climb. It's currently up to 53.5.

This happened to me once during a mash and I was several degrees over what I should have been. It really pissed me off.

Sorry for the music on the video. There were some distracting background noises that I wanted to eliminate.

10-01-2012, 05:04 PM   #4
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All of my PIDs are having this same problem, and I have tried swapping the probes. Maybe it is something that could be adjusted in the settings.

If it helps, here is a copy of the manual and a transcription of all of the PID's current settings:

http://www.rkcinst.co.jp/english/pdf_ma ... zc21e1.pdf

Option -Setting- Explanation
AL1 -000.0- Alarm 1
ATU -0000- Auto-tune
P -12.3- Proportional Band
I -88- Integral Time
d -22- Derivative Time
AR -51- Anti Reset Wind-up
T -2- Heat Side Proportioning
SC -000.0- ????
LCK -1000- Set Data Lock

after the lock I get these options with these settings:

Option -Setting- Explanation
COD - 0000 - ????
SL1 - 1000 - Input Type
SL2 - 0000 - Temperature Type and Cooling Type
SL3 - 0000 - ????
SL4 - 0001 - Alarm 1 Type
SL5 - 0000 - Alarm 2 Type
SL6 - 0001 - ????
SL7 - 0000 - ????
SL8 - 0000 - ????
SL9 - 0000 - ????
SL10 - 1001 - ????
SL11 - 0000 - ????

There are a few other parameters mentioned in the manual, but I don't see them in my settings menu.

10-04-2012, 01:49 PM   #5
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Just looking at your photos I noticed the XLR connections for your probes. Possibly there is a issue with using the wrong connectors for probes. I found this on the auberin website under connectors.

10-04-2012, 01:52 PM   #6
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Maybe this is a better snapshot

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10-04-2012, 07:14 PM   #7
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This is a valid idea. This weekend I'll have to try connecting the probes directly to the PIDs to see if I'm getting the same problems. Good thinking!

10-04-2012, 07:24 PM   #8
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Let me know how it works out. I'm in the process of gathering equipment for my control panel build. I will probably be purchasing those connectors.

10-04-2012, 08:50 PM   #9
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What kind of temp probes are you using? Thermocouple (Type K or J, etc) or RTD (PT100)?
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10-07-2012, 09:43 AM   #10
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Quote:
 Originally Posted by ColeBeer78 Just looking at your photos I noticed the XLR connections for your probes. Possibly there is a issue with using the wrong connectors for probes.
I just bypassed the XLR connecters and wired the PT100 probes directly to PID controller, but I'm still getting the same problem.

I've seen plenty of other people using XLR connectors, so I imagine you won't have a problem with them.

Thanks for the idea though.

Does anyone else have any other ideas about what could be going on?