Good afternoon/morning everyone,
As someone who designs Infrared Thermometers for a living I couldn't
resist responding to some of the comments so far.
Please don't take this as a plug for my companies products, the comments are
meant to be general.
> -----Original Message-----
> From: Chris Maxwell [SMTP:[email protected]]
> Sent: 07 January 2002 16:20
> To: Crabb, John; [email protected]
> Subject: Re: Thermocouple alternative?
>
>
> Hi John,
>
> A possible solution would be to use an infrared non-contact thermometer.
>
>
> They measure temperature essentially by pointing them at the object of
> interest. They have a few drawbacks that I know of:
>
> 1. You need to have visual access to the part or surface of interest.
Yes, this is fundamental to the operation. However there are
fibreoptic thermometers available which greatly help with access. These are
commonly used to measure inside induction heating furnaces for example.
> 2. You need to account for "spot size" since its detector essentially
> integrates all of the infrared in its field of view. The spot size
> changes with distance from the thermometer to the surface of interest.
Variable focus helps here. Also there are thermometers available with
nominally parallel field of view, over a specified useful working range.
> 3. If you are trying to graph temperature over time: you can't just
> glue it in place and hook it to a data logger. I don't know if it would
> be worth rigging up some kind of tripod to keep the infrared detector
> aimed at the point of interest.
Many hand helds come with a tripod mount. Larger types should have all
kind of mountings, cooling jackets , purges etc as required.
> We had one in the lab for a couple of days. It was a handheld, battery
> powered unit about the size of a Palm Pilot. Sadly, I only got to play
> with it a little bit before it was taken away. I wanted to see how
> accurate it was at measureing component temperatures on a circuitboard.
>
Now days you can get relativley inexpensive hand held thermal imagers.
These may be more suited to
pcb work.
> >-----------------------------------------
Ted Rook wrote:
Yep, infrared point and shoot thermometers have some terrific advantages but
another drawback with 'infra-red' instruments, they are calibrated for one
value of surface emissivity. Before relying on the value for precision
measurements you should familiarize yourself with Emissivity.
Only low end products. Consider a thermometer with variable emissivity
compensation.
-------------------------------------------------------------
Jeff jenkins wrote:
I have had difficulty convincing agencies to accept data from non-contact
thermal measurement systems, e.g., infrared or optical. The way that I have
convinced them is to take side-by-side measurements on something that is not
producing strong fields using a thermocouple and the non-contact measuring
device. When they saw that the two devices measured the same temperature,
they were satisfied.
Thermometers are available with calibration traceable to UKAS or NIST
standards. This should avoid such problems.
If not supplied with traceable calibration by the manufacturer (many aren't)
they can be calibrated independently afterwards by an independent lab just like
other test gear.
------------------------------------------------------------------
Benoit Nadeau wrote
>From an earlier life in a commercial EMC testing lab, I had one day this
customer from Quebec City who developped a Fiber-optic based temperature
sensing system. Their web site specifies that it is immune to RF. I think it
is worth to look at:
http://www.fiso.com/temp.htm
These look interesting but note that they are not "non-contact". Not an
issue for applications such as transformer windings, but they are likely to
have a higher thermal mass than thermocouples so care needed with small
components.
------------------------------
I also like John Woodgates suggestion of using precision thermistors.
Very useful for measuring component temps on circuit boards etc.
If anyone one wants any further help with any of the concepts then
please contact me offline.
Best regards
Andy Wood
Engineer- Special products
Land Instruments International
WWW.LANDINST.COM
Infrared thermometry and calibration labs.
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