K type vs rtd - Home Brew Forums
Home Brew Forums > Home Brewing Beer > Electric Brewing > K type vs rtd

Reply
 
Thread Tools
Old 06-17-2012, 02:48 PM   #1
amurphyz
Recipes 
 
Mar 2012
Posts: 61
Liked 5 Times on 4 Posts



Yet another rookie question:
Will k type thermocouples work fine, or do you need to use rtd style. Reason I ask is because I can get k type high quality thermocouples from work for dirt cheap, and can make all of my own stainless bungs to weld into my keggles. Just tryin to save some $$$$, thanks guys and gals!



 
Reply With Quote
Old 06-17-2012, 04:20 PM   #2
arlemaster
Recipes 
 
Jun 2012
Posts: 8

Type K thermocouples will work just fine. They have a temperature range that is way beyond what's needed for brewing, so to ensure the best accuracy, make sure you do your calibrations at the temps that you will want to be sensing. For example, calibrate at 150 degree F if you are calibrating for mash temps.


__________________
-Anthony

 
Reply With Quote
Old 06-18-2012, 02:20 PM   #3
Walker
I use secondaries. :p
HBT_LIFETIMESUPPORTER.png
 
Walker's Avatar
Recipes 
 
Sep 2005
Cary, NC
Posts: 10,987
Liked 101 Times on 89 Posts


The only issue (which may not really be an issue for you) is that the 3-wire RTDs are basically self-correcting as far as error introduced by lengthening the wires or using connectors on the wires. With thermocouples, you have to be mindful of adding more wire or connectors on the path.
__________________
Ground Fault Brewing Co.

 
Reply With Quote
Old 06-18-2012, 02:27 PM   #4
Rbeckett
Recipes 
 
Dec 2011
Bronson, Fl
Posts: 995
Liked 70 Times on 49 Posts


Best approach to Thermocouple is to buy them way too long for the application and trim them to appropriate length when installed. Much better to trim than to add connectors and other terminals in that data stream. I ordered all of mine with a 2 meter lead so I can trim them down to correct length when I install them in the system.
Wheelchair Bob
__________________
What do you mean "no Kidneys"???, WTF now I gotta drink less beer...
Join the Automation sub forum in Electric brewing for a discussion of components and control systems. I did!!!!

 
Reply With Quote
Old 06-18-2012, 03:20 PM   #5
crane
Recipes 
 
Sep 2011
San Diego, CA
Posts: 605
Liked 75 Times on 62 Posts


The reason RTDs have 3 wires for canceling out the wire resistance is because those RTDs have a fairly low resistance and they work by changing resistance as the temp changes. Thermocouples work in a completely different way. They actually generate a voltage by themselves. One thing to keep in mind about thermocouples is that the voltages they produce are extremely small. Therefore they can pick up electrical interference quite easily. The noise that they pick up is then amplified along with the signal. Running them next to high voltage high current lines can mess up your measurements.

 
Reply With Quote
Old 06-18-2012, 03:35 PM   #6
amurphyz
Recipes 
 
Mar 2012
Posts: 61
Liked 5 Times on 4 Posts


Hey thanks guys, all good info, right now I just have the bung welded in the mlt, which had no"control" factor anyway, just kind of a reference since I'm using a herms and not a rims system. I think for my sanity, I will just go with the rtd sensor so it's not a problem down the road. The thermocouples I get only have a 2" lead, so I would have to have a connector there, as well as at the cp, sobi think I would be diagnosing and chasing a problem down the road. Thanks again

 
Reply With Quote
Old 06-18-2012, 10:52 PM   #7
crane
Recipes 
 
Sep 2011
San Diego, CA
Posts: 605
Liked 75 Times on 62 Posts


Yeah. You would need to use K-type TC extension wire to get the signals back to your controller as you cannot use regular copper wire to extend TCs. The cost of K-type connectors and extension wire may be more than just going with an RTD.

 
Reply With Quote
Old 06-21-2012, 10:31 PM   #8
amurphyz
Recipes 
 
Mar 2012
Posts: 61
Liked 5 Times on 4 Posts


I do have the correct k type wire, but the more I read an the more posts I get, kinda getting the drift that the rtd is the better way to go.

 
Reply With Quote
Old 06-21-2012, 10:39 PM   #9
BetterSense
Recipes 
 
Jul 2011
Richardson, Texas
Posts: 1,025
Liked 55 Times on 45 Posts


You are correct. I'm a thermal/diffusion engineer, and will tell you that you use a thermocouple when you have to--when there's no other choice. They are basically a pain. RTD is the superior temperature sensor for brewing applications. Actually there are some diode temperature sensors out there that are even easier to integrate if you are doing your own electronics, but between thermocouples and RTDs, I would take the RTD every time.

 
Reply With Quote
Old 06-22-2012, 02:14 PM   #10
thargrav
Registered User
Recipes 
 
Dec 2009
Huntsville, Alabama
Posts: 821
Liked 38 Times on 35 Posts


You can always wire the thermocouple into a bridge network to increase accuracy.



 
Reply With Quote
Reply
Thread Tools



Forum Jump