This is a bit of a speculative question as I'm not sure how feasible it even is.
Can anyone think of a way of measuring gas flow through a pipe non-invasively?
I'm wondering if it's possible to measure using ulrasound, possibly in the same way I'm planning to measure water flow (still can't find suitable transducers) but my guess is that the level of accuracy and frequency of the ultrasound would have to be orders of magnitude higher than for a liquid.
The only other way I can think of is to place a small, low power heating element against the pipe and then measure the temperature gradient up and down-stream. That makes me very nervous though and I've no idea how you'd calibrate it.
There was a suggestion in Elektor magazine a few months ago, using a small incandescent light bulb as a sensor. You have to break off the glass bulb without breaking the filament, then run a constant current through the filament. Gas flow over the bare filament will then cool it, changing its resistance. So, you can sense a varying voltage across the filament according to gas flow. This is how "mass flow sensors" in car engine management systems work.
Yeah, just a bit invasive for what I have in mind; Gas flow over bare incandescent filament (despite it being theoretically perfectly safe) will tend to make people nervous...
Your not trying to measure the gas flow from Russia to the Ukraine are you?
Seriously you can do it with water miniometers measuring the differential pressure in the pipe along a suitable length. After you have the pressure drop the rest is maths concerning the cross sectional area of the pipe and viscosity of the gas. I suppose you could replace the miniometers with electronic differential pressure transducers but they are not cheap.
Sorry, should have mentioned I'm talking about domestic (town) gas supply.
I'm trying to make this completely non-invasive and so a manometer wont' really cut it (excuse the pun). Something clamped to the outside of a pipe is my ideal scenario.
What about a microphone clamped to the pipe near a natural constriction such as a valve or elbow? Would the gas flow/turbulence make enough sound to be detected?
Initially I thought that a mic wouldn't work because it wouldn't give an idea of volume. However I'm wondering if that in fact isn't an issue as most boilers would use gas at a constant rate...the problem then becomes working out what that rate is.
It also doesn't take into account any gas that may be used for cooking.
If only you'd said that you were trying to measure gas consumption in the home! Could you just look at the gas meter, and watch it going round? I suppose it depends on what type of meter is in use in your country, but at least here, there's a dial that goes round.
Thanks guys.
Knew there was a simple solution to this!
Edit: Just had a check and our meter is one of those where the numbers rotate (like an old digital clock) rather than one with a rotating disc.
Do you think a reflective optical sensor (or rather half a dozen of them) would be sufficient to pick up that movement? I'm guessing it probably would and I could simply count which of the sensors is switching; units, tens, hundreds etc
Edit: Just had a check and our meter is one of those where the numbers rotate (like an old digital clock) rather than one with a rotating disc.
Do you think a reflective optical sensor (or rather half a dozen of them) would be sufficient to pick up that movement? I'm guessing it probably would and I could simply count which of the sensors is switching; units, tens, hundreds etc
You only need to monitor the lowest digit. Increment a counter each time the lowest digit switch. If you have access to the digits you could mark all odd digits with a white dot and all even digits with a black dot. Then you should be able to detect whenever the digit switches with an LED and a photo resistor.
I did read a long time back about people using pizo elements as microphones to pick up sounds well above human hearing and then lowering the pitch uniformly into the audible range. One of the things they reported as sounding interesting was gas flowing in a pipe. So there is some basis for building a sensor around this idea.
I would want to have a discussion with my local gas supplier before I stuck sensors to the glass of my gas meter! Could be easily misunderstood by the meter reader!
