IR Thermometer - How accurate are they?

[stix]

Purchased one of these a while back for testing temperature making r-candy. I tested it briefly and it seemed to work ok, besides, I never really needed or used it, as my frypan knob seemed pretty much accurate enough.

 

Got a new oil filled frypan and the temp gauge is in Fahrenheit (those bloody Americans still haven't seen the light ). So apart from having to convert from celsius (google), I thought I would pull out the old trusty IR thermometer for a well deserved cameo performance. Well, it doesn't make any bloody sense at all!! the temps read way too low!!

 

However, I've read before that "silver" or a very reflective surface can throw the reading out. If that's the case (which it seems like it is)... Well, what a useless piece of equipment that's turned out to be. I may as well shove the bloody thing up my flamin' a*rse - which indecently should read around 37C or 99F!

 

Apart from taking that drastic step, I took a reading in my mouth which registered at about 34C. So one could take the view that the IR thermometer is functioning fine.

 

So if someone else could please confirm my findings, otherwise I may have to test the other orifice and... oh.... sh*t... the humanity!!!

 

Seriously though, A reflective surface screws up the reading? Please confirm.

 

Cheers.

 

[EDIT]

 

As I've been writing this, I've been experimenting with a KNSB mix (KNO3 65 / Sorbitol 35) I've just measured off the actual mix and the temperature is very close to accurate!! - even though the comp itself is white/grey-ish in colour.

 

So I've answered my own question - silver/mirror/reflective finishes do not give an accurate temperature reading when using an IR Thermometer. Looks like I'll have to cancel the appointment with the proctologist. Thank God for that!!!

Edited June 27, 2015 by stix

[mikeee]

All else fails read the instructions.

We have run into this multiple times at the process facility I work at. Absolutely funny explaining to an engineer that one piece of metal bolted to another piece of metal is not going to have a 500 degree differential. A highly reflective surface will give a false temperature reading every time. Seems like the IR guys always want to break the newbie engineer interns in the hard way, every year I see an emergency work order come through to take electrical equipment down for repairs because it is about to melt down.

Shiny new fuses, buss bars, bolts, nuts, anodized metals, liquids etc. will give you false readings. They make adhesive targets that you can apply to shiny surfaces for taking regular readings or just paint it with a flat color.

[marks265]

There is a term for the problem Mikeee describes. It is called emissivity. The amount of reflection of an object will alter the real temperature of an object when measured with a thermocouple for example vs the IR reading that you get. This may help to understand where I'm going.

[mikeee]

Most people provide a blank stare when you provide the term emissivity and then you have to explain reflective

surfaces etc. etc. etc.

 

Emissivity is a measure of the efficiency in which a surface emits thermal energy. It is defined as the fraction of energy being emitted relative to that emitted by a thermally black surface (a black body). A black body is a material that is a perfect emitter of heat energy and has an emissivity value of 1.

[marks265]

How I learned about was when I was trying to read the temperature of waffle irons when on an automated line in a carousel. The newer ones were more reflective and read either hotter or colder than the older darker ones. I can't remember exactly which one was which. Then I did some research and found the term when talking to a supplier. Hence the link I had, because the link could describe it better than I. Temperature measuring can be a real pain sometimes and IR is my least favorite, but it does have its place :-)

[mikeee]

marks265,

 

You should have listened to your mother when she told you not to touch because it would burn you. :-)

IR temperature sensing equipment is a great tool if used properly. There are thousands of applications

used in industrial, commercial and residential applications for IR technologies. The railroad industry uses

automated IR scans to monitor bearing temps on all of the wheels on the trains as they pass monitoring

stations and repair orders are automatically created to repair the cars with hot bearings before they start

fires along the railways. The utility industry monitors energized transformer terminations and insulators

and schedules repairs before the systems go critical. The process plant I work at monitors energized

systems while they are running and generate repair orders on systems that require attention. Any time

you can't touch the material you need the temperature on, IR is usually a viable choice. Some of the better

IR sensing equipment and cameras have adjustments for emissivity. Even the IR technicians take a year or so

to get comfortable with the IR scanning equipment used on site, the cameras they use are about $30K a piece.

We have around 40 high voltage transformers feeding power to around 6000 motors that run 24/7 so we use

a lot of IR monitors and cameras every day to identify problems.

[stix]

Thanks guys for all the good info.

Yeah, I guess in the back of my mind from years back I'd heard of the of the "emissivity" issue (didn't remember or even know the name perhaps - but understood the concept). I recently bought an oil-filled frypan that was calibrated in Fahrenheit - never been tested properly.

I was getting bored of converting (C to F) using google, I should have just printed out the chart. Then I remembered about the IR thermometer, and thought "finally the day has come for the IRT to prove its worth".

 

Things unfolded almost as they were happening, as I tried to post in post #1.

The most ironic and bizarre thing is that I remember when I got my new frypan, I was lovingly cleaning it up on my kitchen bench with soapy steel wool, trying to make it look so "nice and shiney"! as you do... I looked over toward the sink and saw a pile of dirty pots, pans, plates etc... I just kept polishing my frypan.

Edited June 29, 2015 by stix

[marks265]

Yes, I know, that's why I still get burned as I never listened to her either.

 

I once had a service come in with their fancy IR equipment to check for electrical hot spots. Then I followed it up with a nut and bolt check of our buss bar and other service equipment. The IR caught very little in the way of hot spots, one or two items IIRC. On the other hand a physical check for tightness of connections showed oodles of flaws. Some connections were so loose it took about 2 turns to tighten them. The resistance had to be low enough to not create enough current draw to produce any heat for the load required. I spent pretty good cash to see all the fancy reports and pics they gave. In the end a good ole hands on check for loose connections or problems was best for the cash spent.

 

I personally see IR temp readings as a reference for every day maintenance tool. To just haul the thing out of a cabinet and expect an actual true and accurate reading with one of these for any situation is a little ridiculous. On the other hand it depends on a margin of error you are willing to accept. And like Mikeee alludes to it must be used wisely.

 

I guess I just generally hate the darn things for said reasons. If I were to use one I would use it for consistency purposes related to pyro regardless of the reading when applicable.

[stix]

Cheers Mark, thanks for the info.

 

Maybe I could do an r-candy mix with some added carbon black, use the IR thermometer to take readings and re-calibrate the knob to Celsius using a sticker over the old one?

 

It would be nice though to have a thermocouple temp controller - but that would probably cost more than the pan itself. What I'm doing doesn't have to be that accurate. +/- 3degC would be good enough.

Edited July 2, 2015 by stix

[stix]

So after about a month of wrestling with my new frypan and the IR thermometer, I've come to some very unappealing conclusions.

 

What I've been trying to do is refine a process and make it simpler (as you do). The reality is that my process has become more time consuming, less accurate and more detrimental to the whole purpose!!!

 

The r-candy formula I've been using for some time includes carbon black (0.3%) It's used primarily as an "opacifier" it also colours the whole mix black. The consistency is a black soft putty which can be read with reasonable accuracy with the IR thermometer - I think.

 

The major issue I have realised is that my new wonderful oil filled fry-pan is not the way to go. Although the oil gives an even heat, it takes way to long to respond to changes and therefore unwanted caramelisation occurs.

 

I'm not making braised lamb casserole, I'm making r-candy where the sugars can easily caramelise and be detrimental to the overall performance.

 

Where to from here? I should go back to my old classic basic electric frypan and the "ring of fire" but it would be nice to know that the IR thermometer is a standard that can be relied upon in this instance.

 

The ultimate fry-pan solution would be immediate heat control, with the IR thermometer as confirmation.

 

Cheers.

[MrB]

So, what your really looking for is a cheap, induction heated, copper slug, aluminum frying pan? Even heat, fast'ish reactions to changes in adjustments. Cheap, means the amount of copper is small, and hence the heat storage is smaller.

I THINK it should work. But finding the parts...

Good luck.

B!

[stix]

Thanks B! - funny thing is that I did look at purchasing an induction cooker, then decided to get the oil one.

http://www.amateurpyro.com/forums/topic/10775-using-an-induction-cooker-for-making-r-candy/

 

In the last couple of days making a few test mixes, I've been a bit more attentive - turning the device up briefly to melting temp, then straight back down to casting temp (whilst checking with the IRT) The residual heat is enough to do the job. This has worked a lot better.

 

However, I'm going to have to try an induction cooker - just to see if it works well.