What's a good k type thermocouple?

[.p4nzer]

Hi, all. I need 4 thermocouple for my thermometers. Those I have are very very low quality thermocouple and I'm searching a good model to buy, built for at least -100 degrees.

I will use it for phase changes, dry ice cooling and perhaps ln2 next year.

Bye

[ultralo1]

Google omega engineering. k type dosent work accuratley at those low temps, you will need t type

[eligray]

Anyone know of some cheaper, reasonable quality k-types though? I also am interested in such a device as long as the price isn't ridiculous

[n00b 0f l337]

Don't just ice test your thermocouples; is it fair to draw a line with only one point and say its correct?
No, and not even two points are proper, because these things aren't linear factors.

So what to do?
Ice bath.
Boil bath.
Ambient compared to your thermostat.
And!! ! ! !! Something much lower on the temp scale, like dry ice.

It's worth the time to know your accuracy.

[.p4nzer]

Don't just ice test your thermocouples; is it fair to draw a line with only one point and say its correct?
No, and not even two points are proper, because these things aren't linear factors.

So what to do?
Ice bath.
Boil bath.
Ambient compared to your thermostat.
And!! ! ! !! Something much lower on the temp scale, like dry ice.

It's worth the time to know your accuracy.

I know... I have made some try but I haven't an instrument that I can define surely accurate to compare the temps.

I have bought 2 thermometers, each one with 2 k thermocouples.

I have tested them on a dimastech phase change (1/2 hp), without any charge on it.

The dimastech thermocouple, that I suppose has very low accuracy, showed -50 celsius.

The oldest thermocouple I have, showed -40. The newest 2 stopped at -22 and the last measured +14 celsius O_O

I guess the most accurate is the -40 but I can't be sure of it.

At ambient temperature the differences are very little, max 1 degree, but I need them for dry ice benching.

Bye

[eligray]

NoL what do you use? how accurate have your tests shown it to be?

[n00b 0f l337]

http://cgi.ebay.com/Set-of-2-Type-K-Thermocouple-Probe-50-to-250-C_W0QQitemZ250356867986QQcmdZViewItemQQptZBI_Autom ation_Components?hash=item250356867986&_trksid=p3286.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A13 18|301%3A0|293%3A1|294%3A50
I buy those;
At -50C they're 1-2C off.
At -100C they're 3-4C off.
Anything lower I use Omega's. (Like the NCE 3 Stager)

[.p4nzer]

Thanks a lot :D