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Old 09-26-2013, 06:38 PM   #1
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Default Funny Readings On PID?

Ok...so first off, I'm just trying to do a simple PID controller box that will operate a fan for my smoker....nothing too fancy. Had a few questions.

I'm using the Auber PID and the K Thermocouple that was recommended by the electric brewery.

1) The thermocouple has 3 connections. I'm directly connecting it to the PID...it has 2 red and one blue connector. Which should connect wear? Do you need to use all three?

2) My thermocouple is reading off and slow. I put the TC in the freezer last night and walked out this morning to find it reading 67 degrees. Any idea on why it would be off...some setting need adjustment?

3) I know the PID is supposed to control a SSR relay, but I'm only planning on using a computer fan, which probably draws like 40 watts. Is there any problem with directly connecting the fan to the PID or do I need an SSR relay?

4) Anyone ever hooked up a fan to a kamado smoker? Not really sure how I might mount it so though I might ask for suggestions. Thanks In advance for any tips/advice

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Old 09-26-2013, 08:06 PM   #2
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If you have two reds and a blue, are you sure you have a K thermocouple? That sounds like and RTD. If you have chosen the wrong temp probe in set up it will read wrong.

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Old 09-26-2013, 08:25 PM   #3
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Originally Posted by sablesurfer View Post
If you have two reds and a blue, are you sure you have a K thermocouple? That sounds like and RTD. If you have chosen the wrong temp probe in set up it will read wrong.
You are probably right. It seems to work with just 2 of the connections attached...so what would be the purpose of the 3rd connection? I'll grab the manual and see how to change it from a K to an RTD. Thanks
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Old 09-26-2013, 10:29 PM   #4
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Originally Posted by jdlev View Post
...
and the K Thermocouple that was recommended by the electric brewery.
...
Exactly which thermo did you secure? That info is really important.

Also: Which PID did you order from Auber Instruments. That also matters a lot.

I'd like to help but need a lot more info.

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Old 09-27-2013, 09:50 PM   #5
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Surfer was right. Just needed to set it to RTD.

So what can I connect to the PID to power? I read that it can handle up to a small heater under 10amps? I don't need anywhere near that...just a small fan that will probably pull 40w. So how should I connect the computer fan...do I need to go through a SSR for that or can I just plug it directly into the SSR ports on the PID?

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Old 09-29-2013, 02:47 AM   #6
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P-J was right, also. More information is needed. Which PID did you get? What are the voltage requirements of your fan?

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Old 09-30-2013, 05:27 PM   #7
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so what would be the purpose of the 3rd connection?
Short answer: Greater accuracy.

Long answer (stolen from elsewhere): In a three wire RTD one of the wires is connected to one side of the temperature element and the remaining two wires are connected to the other side of the element. The purpose of the third wire is to allow the temperature transducer to compensate for the resistance that the field cable adds to the total resistance in the RTD circuit. A typical transducer uses a Wheatstone bridge arrangement for the measurement circuitry.

Without lead length compensation, the temperature measurement would be off by the amount of resistance added to the RTD's resistance, and given that a typical industrial RTD is only 100 ohms at 0 deg C, the error can be significant depending on the length of the field cable.

By using two signal wires it provides greater accuracy by eliminating any wiring influences/errors.

Kal
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