Large LP Gas Tank Fuel Monitor via Transducer

BraveSirRobbin

BraveSirRobbin

Moderator
I'm in need of a transducer to measure the fuel capacity of a 250 gallon and a 350 gallon LP gas tanks. I need to know the fuel level in these tanks. These tanks run generators during power outages in remote areas.

I was chatting with WayneW and Scrambled this morning and we all kicked around some ideas such as measuring weight, monitoring generator run time to calculate fuel left in the tank, etc... but I'm still wanting a way to show the fuel level in a real time status via a (pressure) transducer (and output this voltage to a data logger).

I have a data logger, solar power system, solar power peripherals (battery, charge controller, etc...), Motorola Canopy subscriber module for communication, data logger, serial to Ethernet converter, etc... for these areas, I'm just missing this one item. I will also be monitoring other aspects of these systems such as generator current, etc...

I was hoping that some members would have experience with this LP gas tank monitor and kindly give me some advice.

HERE is something I was considering, but before I call a vendor, I was hoping I could get some advice here.

Also, I'm assuming that pressure would be the monitor method of choice. As I stated earlier weight measurement isn't a viable option for these areas. If there is another method, please let me know! ;)

Thanks,

BSR
 
LP tanks use a float connected to a dial gauge typically. I purchased a relatively cheap wireless transducer / readout box.
http://www.bakersgas.com/rs228.html

The transducer uses magnetism to know where the gauge needle is in it's span.
http://www.bakersgas.com/rs5909s0273.html

I dissected the receiver to see if it could be hacked. I am sure there is a way, but the unit is "one big chip" to reduce manufacturing cost for large qtys. So, no easy way to see if the data could be grabbed.

From memory, the dial gauge is a standard. That way the wireless tranducer fits as a retrofit.
 
I am not under the impression that pressure is the variable to use.

Propane will always have a liquid phase and a gaseous phase in the tank. The pressure of the gas above the liquid propane won't reflect how much is left. Weighing is most accurate, but a float is the most common method employed, apparently.

Doesn't sound easy as a retrofit, to me.

-AC
 
Hmmm, if a float switch is needed, I imagine I would have to get one specific for my tanks (height considerations)?

I saw the one DavidL mentioned but also figured it would not be an easy hack to suit my needs.

There just has to be a way to do this ;) .
 
BraveSirRobbin said:
Hmmm, if a float switch is needed, I imagine I would have to get one specific for my tanks (height considerations)?

I saw the one DavidL mentioned but also figured it would not be an easy hack to suit my needs.

There just has to be a way to do this ;) .
Click to expand...

My guess is you might not use the receiver, but hack something into the transducer. Some kind of circuit that took whatever the sensor provides and do an analog to digital conversion for RS232 et al. I think you are an EE? I would be interested in same solution.
 
Having just completed a similar project last week, I can chime in. I had a client with a remotely located cabin in the mountains of CO who wanted to be able to monitor his three separate propane tanks from TX. The first thing I did was contact the propane utility company that services his home and start asking questions about how best to go about measuring the level. Their suggestion was to use pressure and to obviously measure prior to the regulators on the tanks. I ordered some Wika pressure transducers from Davis and sprung for the intrinsically safe model as I did NOT want to blow anything up. These were installed at the tanks (all three are arranged about 6 feet from one another). They were 4-20mA models and thus, I just wired two wires from each meter back to an enclosure I mounted to a 4"x4" set with concrete into the ground. The outputs of the meters fed analog inputs on an Arduino micro controller with an Xbee shield and the whole shebang was powered off of solar panels purchased from Sparkfun Electronics. I also built a battery charging circuit feeding a 12v7ah "security" battery so that I could get a couple of days of monitoring without sun. The Xbee modules are using the Zigbee AT command set and the send unit is transmitting serial data from the Arduino about 200' to the cabin. There, the Xbee is connected to a MaxSerial Arduino board from Fundamental Logic and it is connected to the client's HAI panel. This allows for an update of the tank levels every 5 seconds and, using messages I update the HAI and Convergent Living systems. I also use WebLink on a local server (that's up 24/7 to also handle a number of Panny IP camera's DVR functionality). WebLink (and the client's SnapLinks) allow him to monitor messages (indicating levels) and also sends emails when the tanks are critically low. Since the cabin is so remote, we consider anything below 25% as critical and the emails come every additional 5% drop after that. So far, it's only been up a week but, thus far, it's working well. Also, the pressure meters are tracking linearly (fingers crossed, I may need to add some temperature offsets to the Arduino's C++'ish code) with the tank's on board analog meters.
 
I pulled this off a random website:

Does the amount of Liquid effect the pressure inside a propane storage container?

No. And important fact to remember is that since the vapor pressure inside the propane container is governed by ambient temperature outside the container not the amount of liquid inside. A container that is 1/4 full at 80 degrees will contain the same vapor pressure as a container that is 3/4 full at 80 degrees. The vapor pressure is not generated by the amount of liquid in the tank. As long as there is some liquid and not more than 80% liquid inside the container, ambient temperature outside the container will govern the vapor pressure inside the container.
Click to expand...

Brian
 
AnthonyZ said:
Having just completed a similar project last week, I can chime in. I had a client with a remotely located cabin in the mountains of CO who wanted to be able to monitor his three separate propane tanks from TX. The first thing I did was contact the propane utility company that services his home and start asking questions about how best to go about measuring the level. Their suggestion was to use pressure and to obviously measure prior to the regulators on the tanks. I ordered some Wika pressure transducers from Davis and sprung for the intrinsically safe model as I did NOT want to blow anything up. These were installed at the tanks (all three are arranged about 6 feet from one another). They were 4-20mA models and thus, I just wired two wires from each meter back to an enclosure I mounted to a 4"x4" set with concrete into the ground. The outputs of the meters fed analog inputs on an Arduino micro controller with an Xbee shield and the whole shebang was powered off of solar panels purchased from Sparkfun Electronics. I also built a battery charging circuit feeding a 12v7ah "security" battery so that I could get a couple of days of monitoring without sun. The Xbee modules are using the Zigbee AT command set and the send unit is transmitting serial data from the Arduino about 200' to the cabin. There, the Xbee is connected to a MaxSerial Arduino board from Fundamental Logic and it is connected to the client's HAI panel. This allows for an update of the tank levels every 5 seconds and, using messages I update the HAI and Convergent Living systems. I also use WebLink on a local server (that's up 24/7 to also handle a number of Panny IP camera's DVR functionality). WebLink (and the client's SnapLinks) allow him to monitor messages (indicating levels) and also sends emails when the tanks are critically low. Since the cabin is so remote, we consider anything below 25% as critical and the emails come every additional 5% drop after that. So far, it's only been up a week but, thus far, it's working well. Also, the pressure meters are tracking linearly (fingers crossed, I may need to add some temperature offsets to the Arduino's C++'ish code) with the tank's on board analog meters.
Click to expand...

Sensing pressure on an LP tank gives you nothing unless you are already out of liquid. LPG in LP tanks exists in two phases at once, gas and liquid. Pressure will be dependent on the ambient temperature as has been previously stated. The only way to sense liquid levels is with a liquid level gauge and a remote ready face. These solutions already exist commercially. My LPG tank is an old Anhydrous ammonia tank and when I set it up, I added a pressure gage. It basically tells me that there's pressure on the tank and lets me know if the liquid gage is hung up. It was able to tell me when the liquid gage on my tank failed. That's about it's only function.
 
BSR,

How about a camera pointed at the gauge. An inexpensive security camera would probably work. I am thinking about using a webcam on my 500 gallon tank.

Steve Q
 
$hit guys, you're making me rethink my install. As I said, it's been tracking well but I don't want to screw this up...

I'm thinking of buying some of the gauges that David linked and seeing if I can't get a circuit built to read the gauge rather than the wireless base station. If that works out, I'll be eBaying the Wika transducers...
 
Wow, these are all great responses! Thanks!

I had no idea this would be this difficult of a measurement! ;)

If this was for my home, I would hack something in a minute, but this is for a work application (another company/department, not even ours) so I really don't want to put something in place that has not already been proven for a hazardous environment such as this.

I'm starting to think I may have to go with weight, as much a PITA as it will be to implement.

LP Gas tanks have been around a long time, you would think somebody would have come up with a solution for this.

The camera is OK, but I don't really want to implement it as it can cause some security concerns in this area that the tank is in.

Please keep the ideas coming!

Regards,

BSR
 
BraveSirRobbin said:
Wow, these are all great responses! Thanks!

I had no idea this would be this difficult of a measurement! :)

If this was for my home, I would hack something in a minute, but this is for a work application (another company/department, not even ours) so I really don't want to put something in place that has not already been proven for a hazardous environment such as this.

I'm starting to think I may have to go with weight, as much a PITA as it will be to implement.

LP Gas tanks have been around a long time, you would think somebody would have come up with a solution for this.

The camera is OK, but I don't really want to implement it as it can cause some security concerns in this area that the tank is in.

Please keep the ideas coming!

Regards,

BSR
Click to expand...

The remote ready gage dials are just holes where you can get a probe down onto the indicator. You might consider a small pot attached to the dial face with a 4-20mA transducer. that's pretty much what the commercial ones are.
 
86turbodsl, would the existing gauges offer the same "hole" to the stem that's attached to the float? With that ability to mate pots to the geared stem inside, the project becomes stupid easy.
 
I guess I should take another look at the transducer. From recollection....the reason it was magnetic is so that there was no need to open up the propane source during an installation. It already is a transducer. If one can splice into the sensor wires...then it's "just" some electronics to interpret that signal, convert to RS232, and decode.

The other nice thing of the Robinaire package was that it was also wireless. No need to run a Cat5 wire from home to tank. I did take apart the receiver, and on quick look, didn't see a good "data take off" spot within it.

Another look, especially by an EE (which I am not), might make simple work of either tapping into the transducer directly or tapping into the receiver (which would be nice).

The price point can't be beat if it can be used as the basis.
 
86turbodsl said:
The remote ready gage dials are just holes where you can get a probe down onto the indicator. You might consider a small pot attached to the dial face with a 4-20mA transducer. that's pretty much what the commercial ones are.
Click to expand...

Do you have any links to good commercial ones?

Thanks - BSR
 
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