remote gas monitor

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dacflyer
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remote gas monitor

Post by dacflyer » Fri Jan 25, 2008 1:09 pm

i been seeing onthe net that Robertshaw made a wireless lp tank monitor
it is a RS-228

seen it on amazon and a few other sites
http://www.amazon.com/Robertshaw-Wirele ... B000IXILAK

i tried to contact robertshaw, but had no luck..kept getting hung up on..

the sensor appears to be a hall sensor, and i am assuming there is a maganet on the pointer of the gas gauge.

i'd like to make something like this to monitor myself,
the gas gauge is not part of the tank, the needle and face are removable
with 2 screws, so there is no risk of gas escaping, i have had the face replaced before, because the plastic gets old then you cannot read the gauge.

i do not need it to be wireless, i figgured something along the lines of
a hall sensor + maganet + led bar display or analog meter
but i do not know what i will need to be between the hall sensor and the display..i need it to be linear

anyone got any ideas... please no harping / preaching on gas safety
theres no worries of gas and electric interplay at all.. its all isolated.
i just wanna keep it simple here.. thanks

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haklesup
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Post by haklesup » Fri Jan 25, 2008 3:06 pm

Not a gery good image of the sensor but I would guess they use a standard mechanical pressure gague with a potentiometer integrated into the pointer. From there it is straightforward to go to an A/D then to some kind of wireless link

Like this http://www.bestmaterials.com/detail.aspx?ID=15578.
or this http://www.barbecue-store.com/gaslow.htm
Not sure how much torque the pointer can apply, converting by coupling it to a pot may work.

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jwax
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Post by jwax » Fri Jan 25, 2008 4:04 pm

Dacflyer- Call me crazy, but video cameras have gotten waay cheap. I might just have to look into that application! :grin:

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dacflyer
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Post by dacflyer » Fri Jan 25, 2008 5:54 pm

jwax >> ya i know.. but i think thats a waste of a good camera.
i was looking along the lines of sorta techie.

haklesup >> i belive it was with hall sensor, the sensor is not directly coupled to the needle of the gauge..

but the way the gauge works inthe tank..theres a spiral shaft the length of the tank,,and theres a float connected to the shaft,,and it it on a sort of crude rail that does not allow the float to twist onthe indicator shaft.. so as the float rises or falls it forces the shaft to turn...and this is directly coupled to the needle of the gauge.. much like the gauge that goes in the take of many riding mowers..its like a gas cap with built in gauge.. knowhatimean vern....?

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Post by Ed446 » Mon Jan 28, 2008 1:21 pm

Remote reading may not be accurate. I used to read propane meters and tank gauges. The propane people said when opening the dome on the tank to let the dome bang into the tank because it was possible the
gauge could be stuck and by banging on the tank would free it.
Edwin

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dacflyer
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Post by dacflyer » Mon Jan 28, 2008 3:20 pm

i am sure thats possible, but i am not concerned about that problem right now.
mine is working fine, it is a 100 gal tank.

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jwax
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Post by jwax » Mon Jan 28, 2008 4:27 pm

Not a "good" camera, but adequate:
http://www.supercircuits.com/index.asp? ... rodID=4233
You could pipe that video to a TV near you! I'm thinking maybe a pushbutton to a monostable 555 to put power on the camera and an LED for, say 20 seconds.
Not techy enough? Go wireless! :grin:

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dacflyer
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Post by dacflyer » Mon Jan 28, 2008 7:17 pm

naaa, i just want something like a led bar graph or digital display..

E-----F or 0% 100% digital...

but i need to know how to make a hall effect sensor work for a rotating maganet if i glue it flat onto the pointer of the gauge,.

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Dave Dixon
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Post by Dave Dixon » Tue Jan 29, 2008 5:42 am

This is way out there - but I thought I would throw it in for you to consider. I like those temperature strips that give a visual indication of the level in the tank. I have NO IDEA how to use this method for your application, but maybe someone else, that is smarter can run with such an idea! Good luck, Dave

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haklesup
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Post by haklesup » Tue Jan 29, 2008 1:50 pm

Sensing the direction of a nearly static magnetic field with a hall sensor, call me crazy but that sounds like a compass. Try this; Adapt a digital compass to detect the direction of the field made by the magnet on the pointer. Modify the face of the compass display to read E-F instead of N-E-W-S.

In any case, I might start looking at sensors for that purpose. Searching "hall compass sensor" gets lots of hits. You would not need a very strong magnet, a magnetized steel wire might be enough, just needs to be stronger than the earth and anything that may approach it externally.

Older models had a sensor separate from the display. Newer models, they are integrated into the same package but still may be separable.

As for the sticker sensor, that could be adapted by placing optical sensors of some kind along its length. These are unreliable under certain temperature conditions where the contents and container are too close in temp.

Avoiding a potentiometer or microswitch is wise as both of these have an ignition potential since they operate with an electrical gap and can arc under normal operation. You should use hermetically sealed parts if you go this way.

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Post by Robert Reed » Tue Jan 29, 2008 4:10 pm

"Avoiding a potentiometer or microswitch is wise as both of these have an ignition potential since they operate with an electrical gap and can arc under normal operation. You should use hermetically sealed parts if you go this way."

Don't get me wrong here as I agree with you completely. But i am amazed that every automotive gas gauge sending unit I have ever come across (at least up to year 2000) has used an open potentiometer carrying current and I have never heard of one causing an explosion, even when having gone defective to the point of intermittants. I have a defective one hanging on the garage wall now and it looks to be wire wound with an exposed wiper. Why do I keep a defective one hanging arouund? Because it cost me over $200 dollars to have it replaced in my Blazer. I just have to come up with it for a circuit use some day to recover some of my money :sad:

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haklesup
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Post by haklesup » Tue Jan 29, 2008 4:33 pm

One of those TV shows, "How its made" I think, recently featured fuel tanks and made a comment aimed directly at your concerns. They pointed out that gasoline vapors mixed with air were explosive but liquid gasoline or vapors not in the presence of air were not flammable.

I assume the manufacturers have worked out the other contingencies like what about when I have the gas cap off and I am filling the tank. Evidently, the fuel air mixture necessary for ignition never develops in normal gas tank operation.

Myth-busters also touched on this when they had difficulty exploding gasoline fumes http://dsc.discovery.com/fansites/mythb ... about.html Indeed in another episode, they also failed to ignite liquid gasoline with a lit cigarette. They may have had better luck puffing in the right vapor/air mix.

A modest propane leak in a tank housed in a small shed on a still day would be close to worse case for explosion risk. While the risks of a potentiometer igniting a remote propane leak in open air are small, nevertheless, it is a predictable and real risk.

I wonder what the dielectric properties of liquid gasoline are. I am pretty sure it is non conductive but I'm not sure how much. The relevancy; Would a contact arc at all while submerged in gasoline as it would not if submerged in an insulating oil (synthetic or mineral oil) as some high power HV circuits are.

BTW, can anyone give be a concise difference between Flammable and Combustible?

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Post by Bigglez » Tue Jan 29, 2008 6:00 pm

Greetings Hacklesup,
haklesup wrote:BTW, can anyone give be a concise difference between Flammable and Combustible?
Flammable is the ability (ease) to ignite (catch fire).

Combustion is the process of burning (being on fire).

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Post by Robert Reed » Tue Jan 29, 2008 9:00 pm

You are correct about gas/air mixtures for gasoline explosions. Way back when, I operasted a Maritime electronics service and install buissiness and one of the items I installed regularly in large cruisers were "Sniffers" (gasoline vapor detectors) in their bilges. After installation, there was a test performed with a gasoline soaked rag in a small container. This was gently moved about directly beneath the sensor to check the Sniffers operation, which BTW was metered. Surprisingly some quite strong vapors were not explosive, while weaker ones were, although both were combustable. Ideally the explosive content would be a ratio of 14 or 15 to 1 (air to gas) and still retains those properties some what either side of that ratio. But in the automotive gas tanks the potentiometer may be above the liquid level at times and could be surrounded by vapor only. But it probably goes back to what I just printed in that the ratio inside the tank is way too dense for an explosive situation.

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Post by Dave Dixon » Wed Jan 30, 2008 5:42 am

We work on aircraft fuel quantity systems at my job. Most all of them have a tube within a tube that is mounted vertically within the tank. As the fuel level changes, the capacitance changes. This allows for a small signal to measure the capacitance. The tubes have about 1/4 inch spacing which should not allow for any arcing. BTW towards the bottom, there are usually a couple more larger diameter tubes around those two tubes to increase accuracy at low levels. It's a little more complex than that, but that is the general principal. Don't know how to apply that in this case, but thought it might be interesting to some of you all! Dave

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