Inaccurate PID Temperature Readings

[uncrichie]

In 2011 I decided to build a PID controller for the lead pot. I chose the Auber SYL-2352 PID controller. Upon testing and setting the temperature I noticed the temp readings were off anywhere from 200-235F degrees. I was casting bullets in pure lead and alloy with readings of 920-975F degrees. Anything lower and incorrect fillout, any higher and frosting would start. I realized the true temperatures were probably in the 700's. It never really bothered me because I just wrote down what temps on the PID gave me good bullets depending on the alloy.

Well, after 7 years (go figure) its starting to bother me and I want to trouble shoot what is causing the inaccurate readings. The controller seems to be working perfectly except for the goofy readings, it holds temperature very well.

Any of our PID Gurus out there ever hear anything like this? Any ideas?

Thanks, Kurt

[Mike W1]

Not a guru but first thing I'd do is disconnect the TC and short the 2 pins and you should read ambient temperature of the room. If that didn't do it I'd likely try another TC for comparison. After that maybe an incorrect parameter could be the culprit. The PID should be good if it passes that first test though.

[uncrichie]

Hi Mike, thanks for the reply. You just jogged my memory. I should have mentioned when I turn everything on from cold start it reads ambient temp in the garage correctly. Today when I turned it on it read 58 degrees which was a degree or two from my analog thermometer on the garage wall. I will do as you advise and disconnect and jump the thermocouple and see if I get the same type readings.

Kurt

[HATCH]

Where did you get the thermocouple from?

The default setting on most PID is for K type thermocouples.
If the thermocouple is a different type other then the K type then you WILL have the issue you are having.

You need to go into the setting and verify the settings for TC

[uncrichie]

Hi Hatch, I bought it direct from Auber Instruments about 7 years ago with the controller. I don't think I have the literature from the thermocouple so I'm not sure what type it is. What I can do is order another TC of a known type and reset the PID. While waiting for that I can fire up the lead pot and try changing some of the internal PID settings and hope for the best. Thanks for the suggestions.

Kurt

[bangerjim]

After over 45+ years of experience (a true guru) with thermal control devices, it sounds like you have the wrong T/C. Or have the controller programmed for the wrong T/C. Either will really screw up you readings.

Go thru and double check the settings. Is the T/C you have marked “K”? Or what? Many of those cheepo ones are not marked at all!!!!!!!

A shorted controller input (with a paperclip) will read approx room temp. But if the temp compensation in the curves is wrong in the controller, as you get hotter, the error gets worse.

Just order another “K” T/C and make sure programming is correct.

A very inexpensive fix for your system!!!!!!

Jim

[jsizemore]

Did you shorten the leads or add a plug?

[AggieEE]

Google thermocouple color code. Somewhere on the web there is a chart of the lead colors of different types of TCs, what they are made of and temp range. Found it one time when I was teaching a class and we were discussing TCs.

[uncrichie]

Just got in from the garage. I have to tell you guys you are terrific and a wealth of information. After reading Hatchs post I went to Aubers websight and looked through the instructions for my PID. Not knowing what TC I have I started to change the "SN" settings which is the sensor settings. "0" is the default setting for a "K" TC which is where I was getting the 900F plus readings. I changed the setting to "5" for a "J" TC and low and behold I got the readings I should have been seeing from the get go! The 975 degree reading I was used to seeing is now at 758 degrees which is right in the center of the ballpark. Many thanks to all of you. Jim the TC had no markings that I could find, must have been one of the cheapo ones you mentioned. I did order a "K" TC and will compare its readings against the "J" readings, of course with the proper sensor settings.

Thanks again fellas, Kurt

[HATCH]

I ran into that problem when dealing with the Master Caster Factory TC.
It was at 900F and the lead was just starting to melt good

Cast Boolits is where members are suppose to help other members when it comes to reloading questions.

[bangerjim]

Listing the temps you were reading, it really sounded like you had a “J” running on the “K” range.

Glad you found your gremlin! Color codes are great for T/C extension wire and plugs, but many of the cheeeeepo chicom T/C’s are not color coded/marked to the ISO/NIST standards. J/K/T/S/R/N/etc all have different coefficient curves and their own unique usages in industry. “K” is the most common for the lower temp ranges we use in casting. When processes reach the limits of the highest T/C’s, they use optical pyrometers.

Banger

Banger