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CO and CO² Electronic Flue Gas Analyser

Michael/5of9

Jan 25, 2017
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A good day to you at Electronics Point; this is out of the ordinary, I have an electronic flue gas analyser, made by Colwick Instruments Ltd (they are no longer around), it’s called Anagas. The sensor fitted detects CO carbon monoxide only, yet the manufacturer successfully managed to achieve detecting CO² carbon dioxide; I am guessing this was achieved by fitting the BD131 S M (a STMicroelectronics BD131/BD132 NPN+PNP Bipolar Transistor, 3 A, 45 V, 3-Pin) and other components.

This was built over twenty years ago; so the technology and components back then wouldn’t be as available as of now.

I have read that a metal oxide semiconductor can contribute to detecting CO² in the form of a transistor and have uploaded a PDF called Metal Oxide Semi-Conductor Gas Sensors, which confirms this and a link to a video called How MOSFETs and Field-Effect Transistors Work! which explains more on this subject.

It would be good to have this clarified and to know more about how this was achieved, detecting CO², from the components fitted on the two PC boards fitted inside the analyser.

You can see what it’s all about on my Microsoft OneDrive.

I am in the process of fitting a new battery pack and a new CO sensor to this analyser before it goes for re-calibration.

Kind regards Michael
Heating & electrical Engineer
 

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  • Metal Oxide Semi-Conductor Gas Sensors. Abst.pdf
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shrtrnd

Jan 15, 2010
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Your MOSFET/FET video explains how they work. They are electronic components. They have nothing to do (themselves) with the detection of CO/CO2. Your circuit apparently uses them in the electronic circuitry that is
designed to detect CO/CO2. If there is an improvement in your analyzer using MOSFETs, that is due to the design
of the circuit that detects CO2, NOT because a MOSFET has anything to do with CO/CO2 detection in and of itself.
It's been a lot of years, but I used to work on air quality monitoring instruments for a county Health Dept.
Your CO sensor is the only thing that is going to detect CO/CO2, your circuit sensitivity is what will determine
how well that CO sensor signal is amplified. (Apparently MOSFET's are used in the amplification circuitry)
If you believe your CO analyzer is able to detect CO2, I'd concentrate on verifying that, and the accuracy of the
expected reading.
 

Michael/5of9

Jan 25, 2017
13
Joined
Jan 25, 2017
Messages
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Your MOSFET/FET video explains how they work. They are electronic components. They have nothing to do (themselves) with the detection of CO/CO2. Your circuit apparently uses them in the electronic circuitry that is designed to detect CO/CO2.
Agreed; I understand.

If there is an improvement in your analyzer using MOSFETs, that is due to the design of the circuit that detects CO2, NOT because a MOSFET has anything to do with CO/CO2 detection in and of itself.
The MOSFET is ONE of the components to show the strength/percentage of CO/CO2.

If you believe your CO analyzer is able to detect CO2, I'd concentrate on verifying that, and the accuracy of the expected reading.
Agreed; before sending the analyser for re-calibration, could you or anyone else suggest any further uncomplicated tests or renewals that could be done? :)

Thank you; kind regards Michael
 
Last edited:

shrtrnd

Jan 15, 2010
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I'm sure we'd like to help. The problem is that we don't know the original circuit of your analyzer, and we don't know the modification using MOSFETs that is supposed to allow the analyzer to give you CO2 readings.
You intend to send the instrument in for recalibration. With those results, you will have a better idea of it's present
CO/CO2 analyzing capabilities, (or limitations). That would give you a better idea of what you have to work with.
No amount of speculation will compensate for actual test results.
Depending on your requirements, you may find you need better accuracy for whatever laws or monitoring limits you expect to meet, than what your instrument can provide. And you may need to look for a newer instrument. (With specifications from the instrument manufacturer).
I say that because I suspect you are required to meet some specific compliance requirement here.
I just don't see how we can offer advice on prepping the instrument for recalibration without the schematics and
test point voltage readings to verify the instrument's operational capabilities.
We're about as in the dark about what you have as you are at this point.
My advice is to communicate with the recalibration house closely, and obtain the data they produce in the recalibration process to see if your instrument will meet whatever requirements you have as it is.
If you have a manual with a spec sheet on this instrument, compare the recal results with manufacturer's specs,
and see if it will do the job you hope it will do, or if the recal results fall short of the manufacturer specs, and the
instrument requires electronic circuitry repair.
Sorry we can't be more helpful at this point.
 
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