[Stoves] Gas Sensing

Fri Feb 8 15:45:44 CST 2008

Dear Frank,

What is the temperature range for the sensors? Will the gas samples have to
be diluted to cool them?

Best,

Dean

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of frank
Sent: Friday, February 08, 2008 10:26 AM
To: Discussion of biomass cooking stoves; nick at qubitsystems.com
Subject: Re: [Stoves] Gas Sensing

Thanks Bear,
Great collection of detectors.

The two that I purchased are the Qubit S126 Methane and the Qubit 129 
CO. I find they both use the  Figaro Semiconductor  and that Figaro 
supplies  most all.

For our purpose I wonder if it is that important that one detector will 
measure (respond to) several gases? All the gases are combustible and 
should be at zero. So I am thinking we just report as Combustible Gas 
(as CO).  That is CG (as CO).  And we calibrate the equipment using CO. 
Like when testing a mix of sugars the results are reported ( as Glucose) 
so this method of reporting is common.

If we can agree to this we can all use these cheap detectors, have 
comparable results and not be tricked in the future into thinking we are 
just measuring only the gas they advertise the detectors measure. We 
site the Figaro Part number required and have Bear or someone build the 
board.

I like the Qubit because it is a flow through system where you can make 
a loop with [flow through pump][rotameter][mixing cell][injection 
port][detector] all connected using tubing. Flush and fill with air and 
circulate. Then inject increasing known volume of CO and calibrate. 
Break the circle and connect one end to the stack. (Yet to try this)

Qubit also make a CO2 and O2 flow through detector that can work in a 
series. I flush with N when calibrating these. Also the detectors get 
sensitized when in contact with the gas they are to measure so the line 
can be flushed with the selected gas and then connected together to make 
a loop for storage.  One of the detectors are stored best in cold (I 
think the O2 one?) so I place the entire collection in our cold room 
between uses.

I have copied Nick from Qubit so he can correct what I have said : )     
He has been very helpful to me in the past.

Thanks
Frank

Bear Kaufmann wrote:

>Hi all,
>
>Jim Mason recently directed me to the discussion of gas sensing 
>equipment on this list.
>I've been working on developing a gas sensing system for our work with 
>gasifiers.
>The goal of the system is to provide real time data about the operation 
>of the gasifier and to log the data to a computer (from gas sensor 
>components, differential pressure gauge(s), and thermocouples).
>The system consists of an Arduino USB microcontroller board 
>(http://www.arduino.cc) along with electronics currently on a breadboard 
>including 16 12-bit analog->digital channels, op-amp circuits, TC chip,
etc.
>The gas sensing components currently have all come from Figaro and are 
>of two principal types: the electrolytic cells (Nernst) and 
>semiconductor/metal oxide resistive types. I've currently interfaced an 
>O2 and CO2 electrolytic cell (which requires some circuitry as mentioned 
>before to amplify the very small voltage the cells produce). The 
>resistive cells measure different gases that can be oxidized, including 
>CH4, CO, mixed HCs, etc. The CO cell is $14.50, and does have some 
>cross-sensitivity to methane. I haven't yet worked on calibrating these 
>to known gas concentrations, which is of course an important next step. 
>I'm also looking to source IR based sensors and interface them. The 
>system requires dilution with air since the gas stream concentrations 
>we'll be sampling are far above the 10,000 ppm limits of most of the 
>resistive sensors, which is accomplished with a pump and two rotameters.
>
>When searching for sensors to use in the system I developed a 
>spreadsheet of sources that I could find online.
>I've posted the spreadsheet on Google Docs, and it should be accessible 
>with this link:
>http://spreadsheets.google.com/ccc?key=pij8V7pu-JgwtzEMuyk78bg&inv=bear@urs
ine-design.com&t=4575016692417395121&guest 
><http://spreadsheets.google.com/ccc?key=pij8V7pu-JgwtzEMuyk78bg&inv=bear@ur
sine-design.com&t=4575016692417395121&guest>
>Feel free to append this with other sources you may know of.
>My main focus was on individual components, not on complete 
>handheld/industrial systems (though the ITX system at the bottom may be 
>of interest).
>
>Hopefully the above information will be useful to others.
>I can post further details of the system at a later date if others are 
>interested.
>
>Cheers,
>Bear Kaufmann
>
>_______________________________________________
>Stoves mailing list
>Stoves at listserv.repp.org
>http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
>http://stoves.bioenergylists.org
>http://info.bioenergylists.org
>
>
>  
>

-- 
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com

_______________________________________________
Stoves mailing list
Stoves at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org
http://stoves.bioenergylists.org
http://info.bioenergylists.org