Advise on thermocouple

Hi,

I want to calibrate my heatbed. I will be getting a silicone heater with a 100k ntc termistor inside. i'm thinking of sticking it on a 5mm think glass.

I know that the thermistor will be inside the heater and not touching the glass so I want to find the final heat on top of the glass.

anyone have a advise on a thermocouple that I could get ? maybe one that i could connect to my digital multimeter ? (not a Fluke unfortunately)

Thanks

J-F

There are some multimeters that can read temperatures. Not all though - just some. Those will have come thermocouple probe as accessory, and designated place to plug thermocouple in it.

But can not add this function to a multimeter that does not already have it because it needs support circuitry. So i am afraid you may need another multimeter specifically with this function, or some other means to read temperature.

ok, thanks.

I had in mind that some thermocouple came with adapters and you could use something like 1mV/deg. scale.

I found some on ebay that looks good.

for sake of interess : Scientific Digital Thermometer 1 K-Type Thermocouple Temperature Sensor Probe

Quote
Rigor_M
I had in mind that some thermocouple came with adapters and you could use something like 1mV/deg. scale.

Those do exist. Something like this: [www.frys.com]

Why not just get an extra thermistor and hook it up in place of your hot end thermistor for testing the heated bed? That would give you the reading you require.

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Thanks, at that price, i'll just get a dedicated probe ;-)

I was thinking of a thermocouple because its more accurate when reading temperature than a normal thermistor..

I have a couple of those in stock.. i guess I could tape one on the bed to take readings..

Thermocouple usually employs a dedicated IC to provide certain required functions like reference, compensation and amplification. An usual multimeter might have an error like 1-2-3% +/- ~-1-2 digit(s) and that means error addition to the measurement, loosing a lot of precision, and 1mV/deg is quite a low scale for a common multimeter. Personally as a matter of opinion i would rather go for a multimeter which is specified to read temperatures, or a dedicated tool like your link, or even an IR thermometer - well, its just my opinion.

Edit: If you have thermocouples physically, and if you use a firmware which supports chips like max6675 you could make a small board with that chip and have the temp reading over spi. If the firmware does not support max6675 expressly, you can use some other chip which outputs an analog signal, one chip is ad595 and i think there is some other its successor, and with the latter one you can use thermocouples directly to the analog pin, but from experience that may include some crosstalk with other wires (i had like 1-2-3 deg of variation per reading accounted to the noise), whereas with max6675 talking over spi such noise should not be an issue.

Edited 1 time(s). Last edit at 03/24/2014 05:08PM by NoobMan.