# Need help with a good thermocouple!



## James Coburn (Jan 20, 2019)

Ok so ive been doing some modifications on my dynaglow smoker. The only problem i have right now is my thermocouple has a bad swing in it. I set my pid to match it at around 50 degrees when starting up. But once it reaches around 140 my pid was reading about 230. I had to go in and reprogram it just to get the element to come back on. Im using my thermopro to monitor air temp inside right beside the thermocouple. 

My question is has anyone found a good brand thermocouple that doesn't have a bad swing like i did?


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## daveomak (Jan 20, 2019)

What type thermocouple  do you need...  "K" ???

I'm thinking your thermocouple has a bad connection...  either in the tube or the plug...


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## James Coburn (Jan 20, 2019)

daveomak said:


> What type thermocouple  do you need...  "K" ???
> 
> I'm thinking your thermocouple has a bad connection...  either in the tube or the plug...


Yes its a k.


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## James Coburn (Jan 20, 2019)

daveomak said:


> What type thermocouple  do you need...  "K" ???
> 
> I'm thinking your thermocouple has a bad connection...  either in the tube or the plug...


Daveomak...its a brand new one and i soldered the connections onto a mic jack to be able to remove it later to replace. You think there is too many connections? Should i just run it straight to the pid instead?


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## daveomak (Jan 20, 2019)

What I was told, YEARS AGO, you can't solder the connections....   Changes the impedance ...  Thermocouples have 2 different wires that have a mechanical connection...  the wires have a specific resistance...  when they change temperature, the resistance/impedance changes in each wire....  SOMEHOW the change/difference is measured...  those differences are miniscule and solder screws it up... That's the reason thermocouples and connectors have screws to secure the wire connections...    Try that and see if your situation improves...  Hope so...  Clip the wires to eliminate any solder on them...


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## James Coburn (Jan 20, 2019)

daveomak said:


> What I was told, YEARS AGO, you can't solder the connections....   Changes the impedance ...  Thermocouples have 2 different wires that have a mechanical connection...  the wires have a specific resistance...  when they change temperature, the resistance/impedance changes in each wire....  SOMEHOW the change/difference is measured...  those differences are miniscule and solder screws it up... That's the reason thermocouples and connectors have screws to secure the wire connections...    Try that and see if your situation improves...  Hope so...  Clip the wires to eliminate any solder on them...


Makes sense,  thanks a bunch!  I will try that first.


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## mosparky (Jan 20, 2019)

Dave has it very close. There is a miniscule voltage generated by the connection of 2 different metals. The meter or controller is reading this voltage like a really low volt battery. Here inlies the problem. The connections have to be the same metal as the wire all the way to the device. If you connect to a standard plug you add a bi metal junction, thereby skewing the voltage from the true thermocouple output voltage therefore you get false readings. In case you think you will just read the temp by reading the voltage, be aware the voltage output is not linear. Voltage at 80 deg is not twice the volts at 40 deg nor 1/2 the volts at 160 deg.
 The terms on your pid should be color coded. one goldish the other silver. MATCH the wire colors. One is gold or copper color the other is silver.
 There are plugs and recepticles made for this purpose. Pretty sure you will need extra thermocouple wire to wire from the recepticle to the PID. Again match colors. The thermocouple wire is pretty cheap. And an effective thermocouple can be made by simply stripping the ends and twisting together. Thats really all the manufacturer does. then they pot them in a thin metal sleeve with epoxy.


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## daveomak (Jan 21, 2019)

Thanks Sparky.....   I knew it was something like what I noted...  KeRap, I just lerned how to spel elektricity....   Dave


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## James Coburn (Feb 5, 2019)

daveomak said:


> What I was told, YEARS AGO, you can't solder the connections....   Changes the impedance ...  Thermocouples have 2 different wires that have a mechanical connection...  the wires have a specific resistance...  when they change temperature, the resistance/impedance changes in each wire....  SOMEHOW the change/difference is measured...  those differences are miniscule and solder screws it up... That's the reason thermocouples and connectors have screws to secure the wire connections...    Try that and see if your situation improves...  Hope so...  Clip the wires to eliminate any solder on them...


You must have heard right! I ditched the mic Jack and ran the TC directly to the PID and it solved my problem it still isn't perfect but I can live with it for now.


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## daveomak (Feb 5, 2019)

Cool....  I guess my memory, for older stuff, is still working fairly well...  It's a day to celebrate...  HAHAHAHA....


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