thermocouple module

[daviddoria]

i need one that fits radio shack 22-812 multimeter. i believe i need this to measure temperatures (will it do liquids?) i googled it but came up with nothing.

anyone know of one?

david

 

[daviddoria]

hmmm

https://www.radioshack.com/product....1_008_001_000&product_id=910-5611&site=search

found that one....
however it says not liquid submersable...

any thoughts?

 

[glmclell]

it would reduce the response time of the probe some, but you could seal the junction in a bead of epoxy or silicone (depending on what kind of liquid you're wanting to measure)

 

[daviddoria]

i just want to measure water at room temperature and with ice.

you mean just put silicone around the end of the wire that is placed in the water?

 

[John Sorensen]

If this is just for a home hobby experiment thing you probably don't need to worry about it at all. I made thermocouples out of just twisting thermocouple extension wire together and put it in an ice bath (for 32F) and in my mouth (for 98.6F) two point calibration. And I still feel ok.

j.

 

[glmclell]

you mean just put silicone around the end of the wire that is placed in the water?

yes!

if you're just measuring water, you don't have to worry about it really, but your probe will eventually corrode away... so if its just for short term contact situations, you wouldn't need anything at all I guess

 

[daviddoria]

john, what do you mean "thermocouple wire"?

this sounds much cheaper than buying the 40 dollar module....

 

[mechie]

Thermocouple Options ?

The manual for your meter says that it needs a signal of 1mV per degree Celcius so the thermocouple module must be an amplifier with "cold junction correction" and linearisation.
Given the relatively small range of temperatures you want to measure how about usng some other sort of sensor ?

Maybe a silicon signal diode and simple op-amp could be used ?
Maybe one of those temp sensor ICs would be easier ?
:wink:

 

[John Sorensen]

When done properly ( :x ) thermocouple extension wire (the wire that runs from the junction to the monitoring device) is made of the same material as the probe (the junction). (Some very misguided people will run copper or whatever from the probe to the meter, which is so wrong). Anyway, if you get some "thermocouple extension wire", strip insulation off the end, and twist the wires together, viola, it's a thermocouple. Ideally it would be welded, but if this is for a home project, it's good enough. I've done this with type J and type K thermocouple wire. I don't know if you live in the states, but if you do you may be able to go to your local HVAC supplier and ask them nicely for a few feet of the stuff. They may have type T, which is more common for HVAC. Then the trick is just getting something to measure the temp, as the junction will only put out millivolts, which is not linear, and I don't even think it's monotonic. Have you thought about a thermistor, instead? Much easier if you're doing roll-your-own temperature measurements, especially at low temps.

j.