Cheap thermometer calibration technique?

On Tue, 08 May 2007 19:36:52 -0700, John Larkin


Yes.It was me, and a MATTE finish (flat black paint) WILL yield a BETTER surface quality with reference to IR readings than a shiny surface will.
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Miles off the mark, as usual.
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wrote:

At what temperature? You have to consider emissivity with IR measurements. If your DMM/thermocouple reads okay with the input shorted (terminal block temperature) chances are it's accurate enough at typical heat sink temperatures. Chances are your IR is not.
Best regards, Spehro Pefhany
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~130F, max. I am frequently asked to measure the temp of a stack of press output (big 6-color sheet-fed presses) to determine if the IR dryer lamps are functioning properly. Sometimes using an IR gun is fine, but some press operators prefer the traditional method of a probe inserted halfway down the stack. It would be nice if my tools' readings corresponded.
Re. the ice "calibration": as someone pointed out, ice & h2o isn't very IR-emissive, it it? Would it help to mix in a little black ink? (Lots lying around a print shop...)
Thanks,
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wrote:

All that IR from the lamps might be reflecting around and giving you problems too.

It won't mix in (it's oily), that's kinda the point with offset printing. ;-)

Best regards, Spehro Pefhany
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Measurement is taken after printing is done and lamps are cooled (they aren't in direct "sight" of the delivery stack on the press, anyway).

We've got lots of (large format) inkjet printers, too! Would h2o-soluble ink in the ice water increase the emissivity?
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wrote:

Yes, but I don't know how you're going to get a matt finish on the water. More importantly perhaps, the ink might alter the boiling point.
Best regards, Spehro Pefhany
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On Tue, 08 May 2007 15:00:14 -0500, Spehro Pefhany

The term is matte.
Water is a bad idea for the IR, and the color doesn't matter.
The term for today is:
SURFACE QUALITY
http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf
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On Tue, 08 May 2007 17:46:11 -0700, The Great Attractor

You keep posting this link, so why don;t you *read* it?
Water has a thermal IR emissivity of 0.98, about as black as anything gets.
John
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On Tue, 08 May 2007 21:50:48 -0700, The Great Attractor

OK, positively the last time:
IF THE EMISSIVITY IS 0.98, IT CAN'T BE REFLECTIVE IN THE THERMAL IR.
And while you're at it, check your own link for the emissivity of glass. And smooth ice.
John
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["Followup-To:" header set to sci.electronics.design.] John Larkin wrote:

He's proven himself to be both stupid and illiterate, so please be nice and stop riling him by shoving his nose at documents that he can neither read nor understand.
robert
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So where's the "standard" in this experiment?
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Garner some facts here:
http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf
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The probe also has to be calibrated. Ideally, NIST traceable with a correction chart provided.
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If you use a stainless thermos or Starbucks coffee mug thing, and fill it with stirred crushed ice and water, and fire an ir sensor down into that, it should be pretty good.
I've got an ice cube on a paper plate on my desk, just starting to melt. Our FLIR thermal imager shows it at about +0.5C, and a cheap Extech IR thermometer claims -2C.
The emissivity of the ice cube seems close to 1.0. As I image it and wave my hand around nearby, there's no hint of thermal reflections or temperature change, so it's almost totally black in the thermal IR.
Oh my red plastic Presidential Water Cup is on my desk, too, with about an inch of water in the bottom. It reads 6.8C with a thermocouple, 7.0 on the FLIR, and 4C on the Extech. Again, no hint of reflections. So water also looks black at thermal wavelengths.
John
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John Larkin wrote:

Is your FLIR imager one of the cryo-cooled ones, or do you have a newer one (less than a decade old) with the uncooled detector?
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wrote:

It's an E45, about a year old, uncooled. About every 30 seconds, it clicks and seems to close an internal shutter for a couple of seconds, which I assume is some sort of auto-cal of the sensor array.
It's pretty slick, except for the USB interface which is bizarre. It's a network device, not memory like other cameras, and you have to install their strange software to talk to it.
We can focus so close that we can image the hot-spot temp on an 0603 resistor! Imaging an operating pcb can lead to all sorts of revelations.
We looked at the Fluke, but nobody at Fluke seemed to understand it. Not a good sign.
John
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John Larkin wrote:

The internal shutter is for NUC (Non-Uniform Correction) -- focal plane array sensors in general (even visible light) have gain and offset differences from one pixel to the next. Part of it is periodic with the internal structure of the chip or with polish marks. The rest is just purely random. Visible light sensors can be selected to eliminate this to some extent (pro video cameras have nonuniformity correction, but the camera manufacturers won't admit it). IR detectors can't, and the amount of nonuniformity in the uncooled detectors can be astonishing; as of five years ago it could be 100x as much as your intended signal.
So every once in a while the shutter comes down, the internal logic recalibrates the NUC, and the camera continues on.
There are only a few companies that actually manufacture imagers (FLIR Sweden is one). So many companies that "make" IR imagers are just plopping an OEM module made by someone else into their case.
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wrote:

K. Irani invented the "resistor bolometer" back in 1960.
http://www.mikroninfrared.com /
They have imagers, but likely get their sensors from an OEM house, as does FLIR most likely. Chip fabs ain't cheap endeavors.
The best thing about a good IR device maker is the electronics behind the instrument.
FLIR buys their calibration sources from these guys.
These guys are the top dogs in non-contact temperature measurement.
We made some that are still in use at the shuttle launch pads that have the longest IR focal length made for a calibrated instrument.
The observation shacks are 1000' from the pad, and the instruments observe a ten foot spot, and detect a 200 C change within a one foot spot in that circle (1 FOV). The area observed is known as "the protected area". It is near the blast chutes on the pad.
When IR imagery was in its infancy, their device was $90,000, and was 4 frames per second, and we had early 386s back then, and there was not even a way to get the images off onto VHS. At least it was 16 colors.:-] We also had one that looked through a microscope.
Now, they are likely 16 bit color, and the image data can be manipulated post capture. These guys are pretty good.
I used to build a 2.5 foot by 4 inch, gold mirrored, rifle stock and scoped analog unit that power companies used to point at insulators and transformers to get status without having to climb poles or towers.
Now, they just point an imager at them. And a fairly cheap one at that.
The world has come a long way since '87.
Here's a good primer:
http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf
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On Tue, 08 May 2007 12:20:02 -0700, John Larkin

My FLIR rep confirms: water is 0.98.
John
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