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Old 01-30-2013, 07:33 PM   #1
manoaction
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Default Control Box on Wall Instead of Brewstand

I'm working on my plan for an automated system based around a BCS brain.

Originally, I was going to mount everything on the brew stand and just plug the brew stand into the wall when it was time to brew.

Conversely, I'm now thinking about mounting all of the electronic guts on the wall and then just plugging the brew stand into power cords coming from the box on the wall. I like the idea of it being on the way because I could then use it to also manage a fermentation chamber and cold box in another part of the house.

My biggest question is, how big of a pain/expense is it to splice thermocoupler probes, and is it a big problem to extend their wiring. Is this something that's commonly done?

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Old 01-30-2013, 07:54 PM   #2
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I would not suggest splicing T/C wires if at all possible. Everytime you make a connection it creates a seperate cold junction and requires an offset calibration for this. RTD's on the othe hand can be spliced with negligable effects. Visit Omega.com. They have alot of temp probe connectors and extensions if needed along with some nifty panel jacks that will let you plug your probes in to the main panel. Just remember to match types as the temp curves vary from type to type.

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Old 01-30-2013, 08:07 PM   #3
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Hmm... That's what I was afraid of.

Is there degradation when running RTD's long distances? For say like 20 feet over to where my cold box would be?

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Old 01-30-2013, 08:33 PM   #4
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No problem at all. I have ran them in industrial enviroments well over 150 ft with no problem. RTD's are more forgiving but are not quite as precise usually. They are more than adequate for this purpose. When I mention precision I am talking about tenths or even hundreths of a degree.

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Old 01-30-2013, 08:34 PM   #5
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One good thing about Rtds is that you can use shielded Beldin type of cabe to hook them up. You do not need expensive T/C wire.

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Old 01-30-2013, 09:09 PM   #6
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You can extend thermocouples if you use the proper wire and connectors. I would be weary of running one 20 ft though. They produce an extremely small voltage so you need to make sure you aren't introducing any noise by using shielded wire.

Extending RTDs is a better route but you need to take a few things into consideration. PT100s only have 100 ohms of resistance at room temp. Extending a basic 2 wire PT100 can cause problems because the resistance of the wire can throw off your measurements. You can get around this problem by using a 3 or 4 wire RTD. These will compensate for the resistance of the wire when used with a device that has the proper circuitry for these types of RTDs

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Old 01-30-2013, 11:12 PM   #7
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Quote:
Originally Posted by crane View Post
You can extend thermocouples if you use the proper wire and connectors. I would be weary of running one 20 ft though. They produce an extremely small voltage so you need to make sure you aren't introducing any noise by using shielded wire.

Extending RTDs is a better route but you need to take a few things into consideration. PT100s only have 100 ohms of resistance at room temp. Extending a basic 2 wire PT100 can cause problems because the resistance of the wire can throw off your measurements. You can get around this problem by using a 3 or 4 wire RTD. These will compensate for the resistance of the wire when used with a device that has the proper circuitry for these types of RTDs
I didnt know anybody still used 2 wire rtds. I know some places still have them in lab equipment but it is rare in most industrial instrumentation applications. It has probably been over twenty years since ive used them in the field. With a 3 or 4 wire rtds, length is not much of an issue because it uses a basic voltage divider circuit to compensate for voltage drop.
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Old 01-30-2013, 11:39 PM   #8
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PT1000s are better than PT100s because the contribution of the lead wires is 10x less. Better still are thermistors, in the multiples of thousand Ohms, and even better than that are dedicated temperature measurement devices like DS18B20s which have a digital output. And best of all are sensors with radio frequency transmitters that don't use wires at all.

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Old 01-31-2013, 01:25 PM   #9
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Ah I didn't catch that the OP is using a BCS for his controller. In that case I don't know why you are talking about extending thermocouples as the BCS only accepts thermistors. I prefer and thermistors myself. Their high resistance makes the resistance of the wire negligible and they are easy to interface with once you calculate the steinhart coefficients.

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Old 01-31-2013, 04:08 PM   #10
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Quote:
Originally Posted by crane View Post
Ah I didn't catch that the OP is using a BCS for his controller. In that case I don't know why you are talking about extending thermocouples as the BCS only accepts thermistors. I prefer and thermistors myself. Their high resistance makes the resistance of the wire negligible and they are easy to interface with once you calculate the steinhart coefficients.
I didnt notice the BCS comment either. I was just speaking from experience with industrial controls and costs associated with them.
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