Can High Emissivity IR Paint Solve Pyrometer Accuracy Issues on Steel Surfaces?

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Discussion Overview

The discussion revolves around the challenges of measuring the temperature of a steel surface using a pyrometer, particularly due to varying emissivity. Participants explore the potential of using high emissivity infrared (IR) paint to improve measurement accuracy, while also considering the specific requirements for the paint, such as transparency in the visible range and stability across a temperature range of 50-200°C.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant suggests using a high emissivity paint that is transparent in the visible range to address the varying emissivity issue when measuring temperature with a pyrometer.
  • Another participant questions the necessity of the paint being transparent in the visible range, proposing that carbon or soot could serve as an effective high emissivity surface.
  • A participant mentions the specific application of measuring temperature on a drying cylinder in a paper machine, emphasizing the need for transparency to avoid coloring the paper.
  • Concerns are raised about the effectiveness of calibrating emissivity due to the non-uniformity of the surface, with one participant reporting emissivity values ranging from 0.2 to 0.6 across different areas.
  • Some participants discuss alternative methods for temperature measurement, including two-/multi-band pyrometers and pyroreflectometers, noting limitations in their operational temperature ranges.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of the paint being transparent in the visible range and the feasibility of calibrating emissivity. There is no consensus on the best approach to accurately measure the temperature of the steel surface.

Contextual Notes

Participants highlight limitations related to the non-uniformity of the steel surface and the specific operational conditions of the drying cylinder, which may affect the applicability of proposed solutions.

jarra
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I'm having problems measuring the temperature of a steel surface with varying emissivity with a pyrometer. So I thought one way to overcome the varying emissivity is to paint the surface with a paint that has a high uniform emissivity in the IR region.

The paint should:
  • Have high emissivity in the 7-15µm range and be transparent in the visible range.
  • Not change it's emissivity in the temperature range 50-200oC.
  • It is also preferable that the paint is non-toxic.


Does anyone know of a paint that matches these criteria?
 
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Why do you need it to be transparent in the visible?
Otherwise the best easiest high emissivity surface is carbon, soot from a smoky candle or charcoal from a barbecue is about as good as it's possible to get.
 
The surface I'm supposed to measure is a drying cylinder in a paper machine. I'm supposed to measure the temperature while the machine is running. So in order not to colour the paper the paint needs to be transparent in the visible.
It is my master project I'm working on so if anybody have an alternative method on how to measure the temperature I would be all ears.

Thank you for your help!
 
jarra said:
The surface I'm supposed to measure is a drying cylinder in a paper machine.
Non contact ir thermometer is a classic method.

So in order not to colour the paper the paint needs to be transparent in the visible.
Still not clear why it needs to be transparent.
The drying is going to be by contact so as long as it isn't super insulating the paint isn't going to have any effect on the drying.

If the metal is only at 100-200C the peak emission is going to be well out into the IR band so just the metal may be black enough, you could also calibrate the emissitvity by measuring the IR signal and the temperature of the part while it is not moving.
See http://www.raytek.com/Raytek/en-r0/IREducation/ for more info on IR thermometers
 
While drying the paper is in direct contact with the cylinder so if the paint had a colour the paper would probably be coloured as well.

I don't think calibrating the emissivity would work well either. Because the surface is not uniform. When trying to calibrate the emissivity I obtained emissivities in the range 0.2-0.6 for different areas.

I've been searhing the net for pyrometers that are "independent" of the emissivity and I've found two-/multi-band pyrometers, and pyroreflectometers. But they use photodetector sensor that doesn't work in the temperature range 90-200 C.

Thank you again for your replies.
 

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