K type vs rtd

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!

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.

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.

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

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.

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

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.

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.

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.

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