K Type Thermocouple

[ZenEffect]

So, Ive been trying to hunt down a k type thermocouple that will read down to -196C and havent had any luck... been through 6 different "brands" and none read below -182c. I know its not the meter as I have borrowed one from a friend a while ago and was able to read down to -196C.

Is there any specific brand I should look out for to get a higher probability of getting it to read down to the temps I want?

[Buckeye]

None that I have used will read that low either. I am not sure what brands but I think they end up costing a lot more.

I have found no real reason to be able to read that low of a temp, besides just knowing. Just fill the pot up and it will get as cold as it can.

[ZenEffect]

None that I have used will read that low either. I am not sure what brands but I think they end up costing a lot more.

I have found no real reason to be able to read that low of a temp, besides just knowing. Just fill the pot up and it will get as cold as it can.

The idea is to measure the delta between what ln2 boils at vs base of the pot... and also to measure temp swing to see if I can make improvements on my mounting, pot, or thermal interface material.

[Buckeye]

I did have info someplace on better probes but can't remember what I did with it, I will keep looking.

[ZenEffect]

Cool, thanks I appreciate it

[markwrc]

you will need a N or T type thermocouple to be able to read lower than -180oC

[ZenEffect]

just as an update... i bought a Fluke 80PK-1 from my local Frys (right off the shelf)

gave it a test... -197c

[gazza30]

You can get them here from KP's store

[K404]

One of the el cheapo sellers on Ebay has stock of probes that read -196 in LN2. You have to bin them, but at £1 each, it's not a big problem

[n00b 0f l337]

Just order Omega brand. Or order a roll of wire from them.

[ZenEffect]

Just order Omega brand. Or order a roll of wire from them.

i have no way of welding the 2 together. i could do the psu mod, but id really rather not.

[n00b 0f l337]

Actually K types can be soldered with good effect, give it a twist or two then solder.

[ZenEffect]

with like regular solder? will it still read properly at ln2 temps? getting a roll would be optimal if i could solder it... ive got a bunch of mini connector ends that I can recycle from "bunk" k type probes.

[n00b 0f l337]

Yeaaaaaap. The extra interface won't matter because the solder will all be at the same temperature, so won't be producing a microvoltage of its own (or one so low it won't cause any real interference).
For reference in the phase section, Mytekcontrols confirmed this, and solders his own thermocouples and uses them on -150C machines.

The main concern with solder and thermocouples is not for cold, its for hot! Many thermocouples go into industrial processes. So the last thing you want is that solder melting on you. And that's why they weld them.

[ZenEffect]

interesting to know. I can get a spool for way cheaper than a $25 fluke thermocouple. (spool = 10+ thermocouples and cost is around $60... a big win in my book)

i will order a spool today, once it comes in I will relay the results. Im not 100% sure that mytekcontrols has tested them in LN2, but given his and your knowledge, I do not doubt it will work.. it still has to be tested by myself though.

next order of business.... a meter that has a display refresh rate of 4x a second. I found a Chinese one that does 12x a second, data logging, calibration, etc... looked really nice actually.... however no price for single unit, I would have to order 1000 of them

[MTP04]

What meter are you using now?

I use a Fluke 52-2 and find it very quick to refresh but not sure how many times in a second it refreshes. For sure at least 2x but probably more. Before the fluke I used a meter that refreshed once per second and was a pain to work with when try to hold a tight temp range.

[ZenEffect]

va8090, it says 1x per second, but im measuring 2x per second real. I would get a fluke, but the only real advantage that I see is the ability to use a T type probe... which I have no need for now.

[MTP04]

Just checked with fluke and they do update 4x a second.

I know they are pricey but if your not in a rush then just wait for a good deal on ebay for a used one. The cheapest I've seen them go for is ~150 USD. That's for the 2 probe version. The single probe version should be cheaper.

[ZenEffect]

can anybody else verify this? all the documentation ive read says 2x

[l0ud_sil3nc3]

I have two Flukes and neither will read below -187c or so with the other probes reading only -182c or so. Batteries have been changed in both units, and the K type thermocouples are Fluke branded, so my question is how do you calibrate these thermometers or is there no way to do that?

[ZenEffect]

I dont think its the meter I think its the probe. I will buy another one, test it, and send it to you for comparison. I think there may be a difference between the ones that come with the probe vs a probe you buy separately.

I can bin the probes at frys the same way we do cpu's. they had at least 20 probes there so they should have another that reads -196c.

[MTP04]

For sure there are meters out there that can't go lower than say -50c no matter on the probe. My very first meter was like that. The software/chip inside was limited. So when buying unknown meters make sure it says -200 or lower for k type probes.