Sensor Help!!!

Good day to all!

Can anyone recommend me a device/component/sensor that can be used to ~measure the oxygen content of the air?

I have located several distributors that carry the same line of O2 (replacement) sensors, although they have them under different names. E.g Teledyne-ai, Maxtec inc., pacanalytical, .... .However, these O2 sensing devices are a bit too bulky and too costly.

Honeywell also offers an oxygen sensor. Seems smaller than the above sensors. But operationnal temperature is 700oC. It too HOT!!!! too use.

Does anyone know of a ~small device that can be used to get a bearing on the oxygen content of air, albeit not super precise?

Appreciate the help

Regards, Roger

Reply to
Roger Bourne
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A Google search on "" oxygen in air sensor" produced the following

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The first four are all lead/lead oxide electrolytic cells operating at room temperature. The Wikipedia artcle covers this and the high temeprature zirconia and titania sensors, but alos mentions what they call the "oxygen optode" which I knew as the "fluorescence life-time" sensor. This abstract gives the basic infrmation

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In the version with which I was marginally involved, the fluorescence life-time (exponential time constant for decay of floursecenece) varied from 5usec in the absence of oxygen to 1usec in the presence of atmoshperic oxygen. A blue LED can be used to excited the flourescence, and you can use a photodiode to monitor the decay.

The decay was actually monitored by a A/D converter sampling at 4MHz. The LED was pulsed for 5usec every 59 usec, and the whole thing was controlled by a single-chip micro-controller.

The original device was commercially availalbe and used for monotoring the oxygen content of ground water. We wanted to modify it to impove the performance at low oxygen concentrations so we could use it to measure the oxygen content of beer (which needs to be very low). I can't see it in the list of instruments currently offered by my ex-employer.

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Bill Sloman. Nijmegen
Reply to
bill.sloman

Zinc-air batteries require oxygen to function. I wonder if perhaps you could use one of those. Hearing aid sized cells should be readily available.

Reply to
Fritz Schlunder

Have a look at the KE series from Figaro

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Reply to
budgie

Why? Do you care about other (possibly toxic) gasses, or just %O2?

Reply to
Ian Stirling

Hello,

For the time being, I only care about O2%. I might also care (in the future) about %CO2. The aplication for which the sensor is geared for is to monitoring breathing in patients. The sensor should be located possibily in the breahting mask (connected to the O2 tank...), or placed somewhere in the tube that connects the mask to the O2 tank.

Also, what I would REALLY prefer, is a component device rather than a sensor device. This way, cost is reduced and size is reduced. Like I said earlier, this magic component does not need to give an exact reading as long it can give some kind of (electrical preferably) output that varies with O2% input. A cct can always be built to accomodate the component's peculiarities (wishful thinking perphaps...).

Feedback always appreciated

(From the above posts, it seems like batteries are the oxygen-sensor technology of choice. Perphaps, a small battery (coin or button) can be rigged-up in forming some kind of oxygen sensing cct/device. As long that it remains insensitive to other gazes. Too bad I paid so little attention in my chemistry classes... Food for thougth)

-Roger

Reply to
Roger Bourne

I would go abouyt this a totally different way. If you don't care about the possibility of the cylinder being filled by gasses other than oxygen by accident, then I'd put a gas flow sensor into the hose. The basic idea is to have a heated filliment, or in this case, a thermisor would be quite adequate. This self-heats to a degree related to the gas flow, when fed a given current.

Plus, it's cheap, reliable, and is unlikely to fail in odd ways if it gets contaminated. As it's cheap, double or triple redundancy is not a big issue to add.

Reply to
Ian Stirling

Why would the gaz flow affect the temperature of the thermistor? Law of Physics? Common sense? (sounds right, though) Please elaborate.

Hmmm... By how much should the temperature be affected and by what kifd of flow ? Expire or Inspire? Or would they cancel out each other? Raises a new set of questions...

Thermistor== Flow Sensor == indicates if the patient is breating (or not) O2 Sensor == indicates if the O2 tank is supplying the correct O2% or/and indicates if O2 tank is empty

Don't know if I need both yet. I think O2 sensors require flow in order to work well.

-Roger

Reply to
Roger Bourne

A current flow throug hte thermistor generates heat.

This heat causes the resistance of the thermistor to vary. Depending on if the thermistor is positive or negative tempco, and depending on the driving circuit (constant current ofr voltage), a given gas flow over the sensor will lead to a given rate of heat loss to the gas, which will cause a given resistance. (to first order.) Put this in the hose to the mask, and you get an indication of gas flow. Unless someones come along and swapped the cylinders, this is oxygen flow.

You want another sensor in the mask, to measure breathing. Well, inspiration/expiration.

This can eitehr be a fast respondinggas flow sensor, or a simple thermometer, assuming that the enviroment will never hit 37C, or even a hygrometer.

Reply to
Ian Stirling

"Roger Bourne" wrote in news: snipped-for-privacy@u72g2000cwu.googlegroups.com:

An O2 sensor in the tube from the O2 tank will not monitor breathing, only the level of O2, which is constant, at that point.

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Reply to
Ken Moffett

Good point.

Actually, a question that just crossed my mind is: Does anyone know of the basic method/approach that is used in respiration monitors, for the detection of breathing ? if there is such a method (basic, that is).

I been combing through the net trying to find the accepted, standard, "boring", "has-been-done-a-thousand-times" method to measure and monitor a patient respiration, rather than trying to implement the above-mentioned proposed approach (O2 sensors and what-nots), but alas to no avail.

If someone knows a thing or two about repiration monitors, and how the patient breathing is picked...well, I will be grateful for your input :)

-Roger

Reply to
Roger Bourne

Can't say whether this is standard, but one way it has been done: Chilled mirror near nose/mouth/mouthpiece 'fogs' up when exposed to exhalations. This fogging is fairly easy to detect using an LED, photodiode, and associated circuitry. Paul Mathews

Reply to
Paul Mathews

Well, I'm not claiming to "know" anything, but I'd think in an intensive care situation you'd want to rely more on the O2 saturation sensor on their finger. If they're an apnea sufferer, or someone who you're worried about the physical mechanism of their breathing, or want to catch them stopping breathing before it shows up in the O2sat, I'd go for that strap that they use on the treadmills and polygraphs and stuff.

Good Luck! Rich

Reply to
Rich Grise

The method of choice is called capnography. You *don't* look at inspired/expired O2 at all, you measure CO2, usually zero inspired, 5% out, proves breathing and life itself exists. Unequivocal way to monitor respiration in most situations. You can do this by measuring IR absorbtion in a constantly sampled stream of respiratory gas. Commercial capnographs sample at approx 200ml/min. The peak value you get is just at the end of expiration when alveolar gas from deep in the lung is passing the sample point. This is "end tidal" or ETCO2. In normal circumstances this gas is equilibrated with blood CO2, and so is an indirect measure of blood CO2 tension. Which is a tremendously useful assessment of ventilatory function.

Thermistor sensors can work but there is a big dynamic range in that signal according to flow rate past the thermistor, the breath (tidal) volume affects the whole setup a lot. I've made breathing sensors that way, but you either need a fiddly manual zero/gain adjustents or perhaps some clever uP processing to adjust sensitivity. I got moderately useful results using a differentiator circuit to look at rate of change of this signal back when I was playing in a purely analogue way.

Pressure is interesting, modern pressure transducers are pretty sensitive, if you hook one to an airway you can measure a waveform, but again there is a huge dynamic range with this approach according to individual patient TV, I came to the conclusion that I needed more than the basic analogue circuit I built to useful monitor resps this way, again a uP is the way to go.

Mechanical sensors on the chest wall - best forgotten, too error prone.

Pulse oximetry - blood haemoglobin O2 saturation - slow, minutes to respond, poor acute monitor, loads of lag due to the big resevoir capacity of our Hb for O2. Needs some very fancy elecronics to measure acurately.

Hope these few ideas help.

Steve

Reply to
Steve

Thank guys for your suggestions. I am considering the capnography approach (as a method to detect breathing in a patient). Sounds less "bulky" than a closed circuit approach. The pulse oximetry apprach is also very elegant, save that it takes to time react to breathing difficulties (plus, I am not sure if the blood oxygen level can actually tell the number of breaths per minute)

(I guess I was way off with the O2 sensors ;) )

-Roger

Reply to
Roger Bourne

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