Temp probe problems

[Eclectic Ales]

I am having some crazy problems with my thermocouples. They are all reading close to 20 deg off of the correct temp when I am trying to calibrate them. I have all of the thermowells filled with the heat transfer paste that I purchased from GW Kent. I am trying to calibrate them with a cup of ice and water and a digital thermometer that I have tested and is right. I have tried to replace the sensors with different ones and they still read the same close to 20 deg F off. I do know that the thermowells are slightly larger than they should be but I can not replace them because they are welded into the tank. I will be checking the resistance at the sensor and at the cabinet soon to see if they match and compare them to a chart for it. The sensors are pt100's. Has anybody had any crazy problems like this and if so what was the fix?

[Natrat]

Could be hysteresis settings or perhaps sample rate? Is there a filter setting in your menus? That can help stabilize your settings. There should also be a corrective offset...I'm not sure where you are, but I've found that altitude can also throw a curveball

[Eclectic Ales]

There is a calibration but im kinda afraid to set it to that far off. I dont think that sensors should be that far out of calibration. I am not any altitude that would make it matter either so I am a bit stumped on it.

[mkunce]

Re

Check the wire type from the controller to the tank thermometer. It needs to be thermocouple wire - the same type (j, t, etc) as the thermometer lead. Non-thermocouple wire will pick up noise.

[Eclectic Ales]

Thats great to know! I dont think that it is thermocouple wire at all I believe its just plain old wire.

[Eclectic Ales]

Ok so I just checked and mine are not thermocouples but they are resistance temperature detectors. Would this still need to have special wire for them?

[schmogger]

I am using type K thermal wire and with this wire it has to be a continuous length, ie. no splices or pieced together wire. The stuff is not cheap either. Good luck.

[El Superyeasto]

RTD Problems

I use both rtd's and thermocouples in my brewery. My temperature controllers are rtd or thermocouple specific, are you sure your temp controllers are compatible? Should be able to look up specs by model number etc. A couple degrees off is one thing but you have something entirely different going on. Good Luck

[Eclectic Ales]

I have a panel that was built by Brewmation and all they use is pt-100 rtd sensors so I know it will work. I will be checking wiring this weekend and see whats going on if anything.

[El Superyeasto]

Wiring the rtd

I would check the Brewmation wiring diagrams carefully. What model of temperature controller are you using?

[Eclectic Ales]

Its built into the cabinet and its only a temperature module that sends the signal over to my plc. I have checked the wiring over and over and called the company but I still have not figured it out. I think its time to get out the multi meter and get busy.

[Eclectic Ales]

Are these 2 or 3 wire sensors? a 2 wire RTD doesn't compensate for the length of the run from the sensor to the receiver(display). Is there a possibility that the length of your wires is causing a problem with calibration? Are your sensor wires near any electrical wires that could be emanating noise?

It is a 3 wire sensor. The resistanceof the sensors is a good bit off. They are a cheap sensor that i had laying around the brewery that came with my brew system. I contaced Kevin at brewmation about the problem and he was able to point me to the supplier that they use for their sensors. Ill post back with results.

[Eclectic Ales]

I have to say that I'm glad that Brewmation told me where to get the sensors they use from because it totally fixed my problems. The sensors that I already had were reading 114 ohm in ice water when they should read exactly 100ohm. The new ones from Brewmation's supplier read exactly 100ohm in ice water. Problem is solved! Thanks everybody for the help!