Home Brew Forums > Home Brewing Beer > DIY Projects > Brew Stands > K Type Thermocouple vs RTD temperature sensor
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Old 10-19-2009, 02:50 PM   #1
maxbing
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Default K Type Thermocouple vs RTD temperature sensor

I am about to pull the trigger on some PID temp controllers from Auber Instraments. I can't decide on the type of temp sensors to go with K Type Thermocouple vs RTD temperature sensor. RTD is a little more expensive but not enough to really matter.

Does anyone have any advice? Pros or cons of each?

Thanks


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Old 10-19-2009, 03:03 PM   #2
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This link gives a nice comparison of the two: http://www.smartsensors.com/spec.htm

I've seen a lot of posts recommending RTDs for their higher accuracy and linear response. However, it's splitting hairs, IMHO. Both sensors are capable of less than +/-1% accuracy (effectively, less than +/-1.5 degrees at mash temps). For brewing applications, a decently calibrated thermocouple is just fine. I chose thermocouples for my rig, mostly due to the faster response time.


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Old 10-19-2009, 03:05 PM   #3
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In our application I don't think you'll see a lot of difference. Just make sure to match your controller to the type of temperature sensor you are going to get. Here's a chart that tells some of the differences
http://www.smartsensors.com/spec.htm

Edit:
darnit, beat by a couple minutes
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Old 10-19-2009, 03:24 PM   #4
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Nice link,

Thanks guys.

one column made my decision for me...Ruggedness. other than that for the temps we are talking about both look like they would be fine.
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Old 10-19-2009, 05:47 PM   #5
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Thermocouples are just a junction between two dissimilar metals where a RTD is simply a resistor that changes value with temperature. As the previous posters pointed out, for our purposes, it's a non issue. I went with a thermocouple because I found one, for not too much money that had a 1/2" NPT thread on it so I could screw it right into my keggle.
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Old 10-21-2009, 03:23 AM   #6
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The tech at Auberins told me that the RTD coupler is a more accurate sensor. The price difference is not much. What I like about mine is that the actual 1/4" NPT probe is able to be removed from the probe via a quick disconnect. I did not plan on this, just discovered it after I ordered it (to be honest with you I had no idea what I was ordering) after talking to the Auberins tech....who I pissed off with all of my elementary questions.


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Old 10-21-2009, 06:12 AM   #7
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RTD is my vote. They offer more repeatable readings over time, and thus more robust in my opinion. I use 3wire RTDs that compensate for the resistance of the wires, which is important if you want to use long runs like I do. 4wire will compensate for different resistances between the wires.

Doorbell wire is a cheap source for wire... get some quick connectors from omega they are only a couple of bucks. Mine have 1/8mpt which I thread into 1/8fpt - 1/8straight thread. A silicone oring and a nut are used to make watertight connections. That's how I modded my stainless conicals to monitor temperature of the beer. I use a dial probe on the kettle... only used to gauge approach to boiling. Good luck!
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Old 11-01-2009, 07:39 PM   #8
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Default Thermocouple Types

Any thoughts on the type of thermocouple to choose? J vs K vs T ect?

Also, I'm thinking about ordering from omega since they seem to have better quality than the Auberins ones I've gotten. The question is the configuration. I can get a connector on the end of the probe, braided line with a connector on the end of the line as well. Does anyone have the connector at the end of the probe? If so, do you like it?
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Old 11-01-2009, 10:03 PM   #9
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Quote:
Originally Posted by StMarcos View Post
RTD is my vote. They offer more repeatable readings over time, and thus more robust in my opinion.
Not true. You can't change Physics. A junction between between two dissimilar metals will always induce an EMF and unless the two metals change their chemical composition over time the EMF will stay constant.
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Old 11-02-2009, 12:14 AM   #10
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It is true. There are more sources of drift in a thermocouple than in an RTD. They are also more accurate.


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