Thermocouples in the kitchen

[Boulevardier]

Having had various temperature problems with our expensive (AEG), but now 10-year-old, oven, I have bought a cooking thermometer which uses thermocouple probes. The instructions say that it is for measuring food temperature, not oven temperature. Is there any reason that a thermocouple probe wouldn’t be able to measure air temperature in the oven? After all, air is a fluid and I thought that measuring fluids’ temperature was what thermocouple probes do well.

I know that measuring surface temperature is a general problem for thermocouples (and anything else), but thought fluids were straightforward.

Any thoughts or experiences?

Mike

[broadgage]

Two possibilities.
Firstly there must be a limit as to the maximum temperature that the instrument can stand. The very hot air in the oven might exceed this limit.
The food will be less hot, seldom much exceeding 100 degrees.

Secondly, if the probe must be removed from the oven to read it, it might cool down too quickly to permit of an accurate reading.

[Boulevardier]

Seems pretty clear from the instructions that probe and lead is capable of withstanding oven temperatures - it's designed to be left inside the hot oven, with the lead coming out between the door seal and the oven body. This also means that the oven doesn't have to be opened to read temperature - which is displayed on an external unit.

Mike

[John10b]

That’s an interesting question.
I can say that type K TC can be used to measure the temperatures inside very hot containers. Some times a small slug of metal is fitted on the tips to smooth out the very rapid fluctuations that can occur, this would depend on set specifications and the objectives.
For longer more permanent installations RT an other sensors can be used.
Again this all depends on the design and requirements.
Cheers
John

[Bazz4CQJ]

This sounds a lot like they are just covering themselves against some crazy legal claim. The temperature inside an over can vary significantly, even with a fan-assisted one; scientific ovens go to some expense to achieve uniformity. So just placing a single TC at some arbitrary place may or may not give you a good guide "oven temperature".

Another grey area; what is the outer covering of your TC? A K-type TC in a steel sheath will go to far higher temperatures than domestic oven will see, but a TC covered in PTFE, for example, should be kept within certain limits, as was discussed recently on the forum.

B

[Boulevardier]

The probes are steel-sheathed, and the cable sheath is metal-braided, so should be OK.

I can’t see either why it wouldn’t work to measure air temperature. Apart from the manufacturer's instructions, I was also led to ask the question by the fact that they are just about always described as “food thermometers” rather than “oven thermometers”, and the descriptions only talk about sticking the probes into food. I also came across a cooking forum in which people were bewailing the fact that it wasn’t possible to buy an oven temperature thermometer, because they were all food thermometers – that also puzzled me.

Mike

I wanted to cook a piece of lamb at 55C for hours, I tried measuring the oven air temperature with a thermocouple, it was all over the place. Did the same with the measuring bit inside a glass of water, a much better result.

The result was a lovely soft (eat it through a straw softness) pink Christmas lunch, even mother in law who is a good cook said so, praise indeed.

[Boulevardier]

"I tried measuring the oven air temperature with a thermocouple, it was all over the place."

That's very interesting, and might bear out the impressions I've picked up that TCs don't work in air. Anyone any idea why that should be?

Mike

TCs do work in air, it was (is?) the oven control.

[ex seismic]

I used to use metal cased K type thermocouples to measure air temperature in industrial process drying plants usually running in the low hundreds of degrees C. They work quite happily but as has been mentioned there can be surprisingly large variations depending where the probe is in the air flow. I'm sure the same would apply in an oven especially a fan assisted one. To get an "accurate" reading either average a number of probes or as we did plot the temperature profile across a duct and use a single probe in a position decided by a consensus of those involved.

[Terry_VK5TM]

Originally Posted by merlinmaxwell

...it was (is?) the oven control.

I thought ovens still used the oil-filled capillary type thermostats (disregarding the you beaut fancy modern electronic stuff).

Everything we have bought last 3-4 years has still been the capillary style.

[John10b]

The set up for measuring temperatures inside a container, some as large as ISO containers, will depend very much on the material used, the engineering and technical specifications required, and what will be stored or transported inside and for how long.
As previously mentioned large fluctuations can occur, As ex seismic mentioned you can place several sensors inside and get some sort of feel for the “average” temperature. In some cases this will be acceptable but if you were to be transporting other more “sensitive “ material you may have to be more accurate.
This is were the full specification of the requirements come into play and tests carried out.
All very interesting and a bit far away from cooking a joint of meat in the oven.
Cheers
John

[Refugee]

All the food thermometers I have seen in recent years have the display and electronics firmly fixed to the thermocouple so would be unsuitable for measuring ovens.

There are mechanical dial gauge type too I have one, never needs batteries but the oven opening to see the reading.

[Refugee]

The very early ones just had a bi-metal strip and dial.
They were indeed heat proof.

[emeritus]

Hot air rises, and even in a fan oven the top will be hotter than the bottom. Non-fan ovens will have significant temperature variations with height. Mum's old " Radiation" cookery book for her original gas oven pointed this out, and provided suggestions as to which dish should go on what shelf when a number of items needed to be cooked at the same time.

[Brigham]

Do new cookers not come with oven temperature gauges?
My Jackson has a mercury thermometer mounted on the oven door.

[Refugee]

Our oven came without a conversion table for the new fangled metric temperature dial

[AC/HL]

That looks like one of mine a while ago. I misread the controls and switched the grill on rather than the top oven. Pictographs again!

[Terry_VK5TM]

We've got a four-legged garbage disposal unit for days like that