Explosimeter??

S

steamer

Guest
--Saw this on ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=300375335943
--Question: this looks a little 'old school'; is there a solid state
contraption that does the same thing, maybe with an output a PIC could
'read'??

--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---
 
steamer wrote:
--Saw this on ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=300375335943
--Question: this looks a little 'old school'; is there a solid state
contraption that does the same thing, maybe with an output a PIC could
'read'??

You can sense (some) combustible gasses with 2 platinum
Click to expand...
wires.
One wire inside a closed space with clean air, the other
wire in the air to be tested.

Heat both wires with the same current, then if the second
wire is in contact with combustible gas, it will become
hotter then the one in clean air.

Measure voltage across a balanced circuit, and voila! you
have a detector.
 
On 07 Dec 2009 18:51:48 GMT, steamer <steamer@sonic.net> wrote:

--Saw this on ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=300375335943
--Question: this looks a little 'old school'; is there a solid state
contraption that does the same thing, maybe with an output a PIC could
'read'??
Click to expand...
There are a number of combustible gas detectors available, some
designed for specific gases (LP, natural gas, etc). Most of them can
be interfaced to a PIC, but the key word here is CALIBRATION. The
commercial units require regular calibration (because the sensors age
from being heated, among other things) and a homebrew version would
only be as accurate as the "typical" ratings of the sensor(s) used -
unless you submit the unit to a calibration service.

Sensors are available from Futurlec:
http://www.futurlec.com/Gas_Sensors.shtml

John
 
Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> wrote:
Measure voltage across a balanced circuit, and voila! you
have a detector.
--Not good enough; that's how the current scheme works but it only
Click to expand...
tells me if there's a non-air mixture, not if it's explosive..

--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---
 
--Thanks; will check 'em out.

--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---
 
steamer wrote:
Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> wrote:
Measure voltage across a balanced circuit, and voila! you
have a detector.
--Not good enough; that's how the current scheme works but it only
tells me if there's a non-air mixture, not if it's explosive..

Yes it does. The platinum wire catalyses the oxygen/gas
Click to expand...
mixture, and thereby increase the temperature.
The other wire does not, and stays at a lower temp.
A temp difference between the two wires signals a
combustible mixture, and detects flammable/explosive gas.
 
--Well I still have an issue with false positives, unless there's a
linear relationship for output. I guess I could search for a specific temp
for a specific mixture then??

--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---
 
steamer wrote:
--Well I still have an issue with false positives, unless there's a
linear relationship for output. I guess I could search for a specific temp
for a specific mixture then??

You have to compensate for temperature, and I fear for
Click to expand...
pressure and humidity as well.
I think that thats the reason sensors in this field are
so expensive......
Also, the higher the wire temperature, the more sensitivity,
but the platinum wires might not like that.
Altough it is these kind of things, that make working in
research a pleasure. :)
 
In message <4b1e9ee5$0$1668$742ec2ed@news.sonic.net>, steamer
<steamer@sonic.net> writes
--Thanks; will check 'em out.

Might also be worth checking out oxygen fuel cells, they'd allow you to
Click to expand...
measure the amount of o2 in the atmosphere, possibly enabling you to
calculate the ratio of flammable gas to oxygen and determine if it's an
explosive level.

--
Clint Sharp
 
--Heh. I noticed that there are a variety of sensors, including one
specific to CO; I wonder if, using two sensors, I might be more able to
'bracket' the value I'm wanting to detect, or is this redundant info..

--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---
 
On 2009-12-10, Clint Sharp <clint@clintsmc.demon.co.uk> wrote:
In message <4b1e9ee5$0$1668$742ec2ed@news.sonic.net>, steamer
steamer@sonic.net> writes
--Thanks; will check 'em out.

Might also be worth checking out oxygen fuel cells, they'd allow you to
measure the amount of o2 in the atmosphere, possibly enabling you to
calculate the ratio of flammable gas to oxygen and determine if it's an
explosive level.
Click to expand...
stochiometry is not critical for explosions. it's more the partial
pressure of the explosive fuel and the partial pressure of the oxidiser need
to be above some limit.
 
Jasen Betts <jasen@xnet.co.nz> wrote:
stochiometry is not critical for explosions. it's more the partial
pressure of the explosive fuel and the partial pressure of the oxidiser need
to be above some limit.
--Soooo could I still use these same type of sensors to interpolate
Click to expand...
mixture or should I be looking to a different solution?


--
"Steamboat Ed" Haas : Currently broke and
Hacking the Trailing Edge! : looking for a job...
www.nmpproducts.com
---Decks a-wash in a sea of words---
 
In message <hfvtt5$sjm$1@reversiblemaps.ath.cx>, Jasen Betts
<jasen@xnet.co.nz> writes
stochiometry is not critical for explosions. it's more the partial
pressure of the explosive fuel and the partial pressure of the oxidiser need
to be above some limit.
Ahh, OK. I googled 'partial pressure' because I didn't recognise the
Click to expand...
term. If you're testing for a specific gas or set of gases then the
concentrations can be predicted from the differential pressures though?
If that's the case then the catalyst/fuel cell method would still work
wouldn't it? (Not being obtuse, just trying to work something through
for my own curiosity now)
--
Clint Sharp
 
On 2009-12-12, steamer <steamer@sonic.net> wrote:
Jasen Betts <jasen@xnet.co.nz> wrote:
stochiometry is not critical for explosions. it's more the partial
pressure of the explosive fuel and the partial pressure of the oxidiser need
to be above some limit.
--Soooo could I still use these same type of sensors to interpolate
mixture or should I be looking to a different solution?
Click to expand...
the platunum catalyst hot-wire sensors work by oxidising fuel the gas,
and so, they are testing for the presense of both fuel and sufficient
oxygen.

the tricky bit could be finding one that can sense mixtures that
are rich enough to be explosive.

these ones might work for you http://jaycar.com/productView.asp?ID=RS5610
 
On 2009-12-12, Clint Sharp <clint@clintsmc.demon.co.uk> wrote:
In message <hfvtt5$sjm$1@reversiblemaps.ath.cx>, Jasen Betts
jasen@xnet.co.nz> writes
stochiometry is not critical for explosions. it's more the partial
pressure of the explosive fuel and the partial pressure of the oxidiser need
to be above some limit.
Ahh, OK. I googled 'partial pressure' because I didn't recognise the
term. If you're testing for a specific gas or set of gases then the
concentrations can be predicted from the differential pressures though?
If that's the case then the catalyst/fuel cell method would still work
wouldn't it? (Not being obtuse, just trying to work something through
for my own curiosity now)
Click to expand...
in gasses partial pressure the equivalent of what concentration is in
liquids.
 
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