Temperature Measurement of Aluminium Bars

Hi Guest,

With the help of radiation tube and pyrometeter you can measure the temmpeprature of aluminium billet

http://www.temperatures.com/rtapps.html

The Fluke, (Raytek), IR thermometer you used is laser pointed device. The laser does not do the temp. measurement, only there to aim. The actually temp. measurement is infrared.

The reason you get such a large discrepancy against the TC is that the emissivity adjustment was incorrect.

Check into perminant mounted devices from IRtek:

http://www.irtek-temp.com/index.php

and Raytek:

http://www.raytek.com/Raytek/en-r0/ProductsAndAccessories/?trck=google

Once these are setup correctly, they are accurate and dependable.

thanks for the reply's,

just one little question, does the emmisivity vary from different types of alloys? The collor of the oxidation layer can vary from light gray to black.

"currently we use thermocouple needles that are placed between the coils of the oven to measure the temperature."

If you are placing your thermocouples between heating elements how can you possibly be getting an accurate reading of the actual temp. of the bars?

If you have varying surface finishes, that could, influence the emissivity of the product, especially if there is ambient light involved.

It's good that you registered, welcome. It's also good that we know your location, as it can affect the answer.

IRtek, is a European company, (Italian I think). I have several of their handheld devices and are reasonably happy with them. I'm not sure if they make permanent mount devices, but you should look into that. I know Raytek, (Fluke), does, and they are international.

You would be best advised to contact these manufacturers, (and google for others). They will be more than happy to assist you, and answer all questions that you have.

Certainly, with this type of device you can get a more accurate reading than the procedure you are using now.

Good luck. Feel free to ask any questions that you have. And do keep us posted!

"If you are placing your thermocouples between heating elements how can you possibly be getting an accurate reading of the actual temp. of the bars?"

the type of thermocouples that we use is made of 2 seperate elements. they have to make contact to the aluminium to get a reading. the time they are not used they are extracted from the oven.

"If you have varying surface finishes, that could, influence the emissivity of the product, especially if there is ambient light involved."

by varying surface finishes, do you mean the type of material like AL6061 or AL 7005 or if its glossy or dim?

In march there is a maintenance fair so I guess i'll get some information there from different vendors

greetings

Oh, I see, I was just confused about TC placement. I don't think the alloy will make much of a difference, glossy or dim might.

Do your homework before you go to that show, so you can ask all the right questions.

See if you can get a company to come to your plant, and give a demonstration.

Hi,

temperature measurements seem never be correct.

If thermocouples: there is a coupling of part to thermo-element this will vary with contact force and dirt and scale and roughness.

And there is a coupling of thermo-element to instrument (that is at Lab temperature).

These couplings are to be interpreted as thermal resistances: Rth to be measured in K/W or delta-temperature/heat-flux.

So we have the following system: a part with a temperature (may be distribution) and an internal thermal resistance (Rthi), a first coupling to the thermo-element (Rth1), some heat-flux flowing along the thermo-element-wires (Rth2) to the measurement amplifier.

So we have a resistive divider from Tpart over Rthi and Rth1 to the element (Te) and from the element along its connection or Rth2 to the temperature of the input (Tamp).

This is totally equivalent to a resistive voltage divider.

You are measuring Te but you want to measure Tpart. So calculate.

Make a check if you are near true by using thinner or thicker thermo-element-wires.

The place where you measure is one of the worst places you can think, the coils have a lot of resistive heating and sometimes internal water cooling.

But the temperature of the coils is not a direct measure of the temperature of your billets.

Coupling of the HF-field and its distribution and resistivity of the billets will have a big influence.

So try the above and try to place the thermo-elements between two billets.

RHABE

Two comments. First, in order to accurately use a thermocouple, the thermocouple junction must be at the same temperature as the item you are measuring. One good method of assuring this is to drill a hole in the item and insert the thermocuple into the hole. The depth of the hole should be at least 10 times its diameter. This is called a thermowell. There are other methods such as clamping the thermocouple to the ingot, but the thermowell is the most accurate and should be used as a standard. With regard to infrared measurements, emmissivity correction has been mentioned, but equally important is to remember that the temperature you read is an average of what the radiometer sees in its field of view. To obtain an accurate reading, the whole ingot must be in the field of view. Otherwise your reading will be part ingot temperature, and part background temperature.