K-type thermocouple

According to the thermocouple theory at

it shouldn't make any difference if a fair bit of the thermocouple wire's exposed to the high temperature. Does it correctly read 100C when you measure the temperature of boiling water?

...was the sensor in the middle of the oven or near the element / flame / fan inlet?

I imagine the temp may be a lot higher near the element/flame/fan inlet than say in the middle of the oven.

The boiling water test suggested by Bob is a good idea, also maybe iceblocks in water continuously stirred should give close to 0C.

Or hold it tightly in your hand, should be about 32 degrees C.

than

iceblocks

A crushed ice "slushie" is the usual method for zero C. Ice blocks in water will be "close" as you suggest. In both cases the water should be as pure as possible.

However calibrating at 0c and 100C, will not guarantee accuracy at 300C oven temperature. In any case the position of the sensor in the oven is likely to be the biggest problem. Shielding from any direct radiated heat may help.

MrT.

That's how I ALWAYS calibrate them.

Graham

Would indeed have to be continuously stirred. Ice itself may well be much below

0C.

Graham

I have found K-type thermocouples to be very reliable. Even with those cheap Asian multimeters. Maybe a degree or two out at most, but good enough for general stuff.

I commend them to you.

Graham

I didn't use boiling water, but I did use an ice cube. It was within

1 degree. I'm fairly convinced that it reads accurately, at least when using the tip, but I wasn't sure what effect exposing the whole length of wire to the temperature being measured would have.

I'll read up on the theory, thanks.

I wanted the sensor near where the oven thermometer was, so that was in the middle of the oven. I made sure the wire didn't run any closer to the element than the oven thermometer. However, the meter was obviously outside the oven, so the wire had to run through the door, where it was in contact with the metal of the oven. This perhaps affected the temperature measured.

Thanks

This may have been an issue. The oven thermometer is shiny metal, but the coating on the wire, other than the tip, was yellow.

After all the previous responses, FWIW... It's likely that the reading you're getting corresponds to the actual temperature of the t/c. The main error is likely to be radiative heating of the sensor, if you can shield it from that you're likely to get a good reading at the measurement point you choose. Oven thermostats and controllers are likely to be pretty rough, and as has already been pointed out, the temperature's unlikely to be uniform throughout the oven.

Why worry if it cooks OK?

Because it doesn't. :-)

"Taylor"

** Gas or electric ?

Element at the top or bottom ?

** Bead or metal rod ??

Does help a tad to be specific.

I suppose it's completely out of the question for you to reveal the make and model of your " probe ".

Why spoil a good troll - eh ?

.... Phil

Water only boils at 100C when the atmospheric pressure is 101.3kPa. If you are above sea level, water will boil at a lower temperature. At

1000m above sea level, water boils at only approx 95C.

David

Electric.

Bottom.

Bead.

Yes thank you. It's close enough for me though on an average day at close to sea level.

Graham

locks

below

Grahams right (for once) but if the bath is continuously stirred so that the water is moving all the way through the ice (or a least through the ice in the immediate vicinity of the sensor) and the water is pure (or at least de-ionised) the temperature is 0C plus or minus a few thousandths of a degree Celcius/Kelvin.

If you dig through the American National Bureau of Standards web pages you could find a more detailed exposition (I did the last time I looked but that was about five years ago).

-- Bill Sloman, Nijmegen