Hi,

My name is Ole Knut and I am responsible for developing the bikes we use in our Racing team. Our sport is roadracing.

I need a method of measuring how much fuel we have left in the fuel tank so we easily can see how much fuel to refill when preparing the bike. The tank holds 10 litres when filled to the max. To keep the weight down, we only want to have enough fuel to run the laps we need to. To reduce the risk of explosions or fire in case of an accident, it's required to put a special foam inside the fuel tank. Because of the foam, I don't see it feasible putting a measuring device inside the tank. We only need to know the amount of fuel left when the bikes are in the pits, so the solution is not required to work good also when the bike is out on the track.

A couple of days ago I learned about hydrostatic pressure. So I got the idea of connecting a dp transmitter to the fuel hose outlet in the bottom of the tank. We have a 12VDC datalogger with display which will accept a 4-20mA input from a transmitter.

My questions are: Will a dp transmitter solve what I'm looking for here? Can you please recommend some small and low weight dp transmitters I could consider?

Thank you.

Regards
Ole Knut Tobiassen
Snoopy Racing
Norway

 

It might, the foam and any baffles that prevent leveling might mess your up and that isn't very much pressure. Will your mounting permit a load cell to measure weight?

Regards,
cww

 

Just a thought....Instead, how about measuring the fuel actually consumed using an on board flow meter? From a known quantity starting point, the remaining fuel can then easily be calculated.

Gerald Beaudoin

 

I don't think a load cell is any option. It would require modifications and we're not allowed to modify anything. It's a stock class. But I think I might get away with adding a dp transmitter to the fuel outlet. I'm not that afraid the foam will prevent leveling. I'm only after an easy way of detecting how much fuel we have left when the bike is in the pits. No matter what happens, the fuel will have lots of time to level inside the tank. What I'm wondering about, is if dp transmitters are able to measure so small quantities as 2-6 litres with a certain precision.

And how much does a dp transmitter suitable for my use cost? If it's cheap, it's just a matter of trying. I guess I'd rather soon will find out if it's reliable or not, by doing some tests in the workshop.

Thanks.

 

Hmm. Might be doable. The amount we usually target for, varies between 4 and 6 litres. I guess we then would need some kind of display and some kind of logic so we could input "start value" and watch current value.

I don't think we can make this logic inside the datalogger device we're using - GPx Pro. It will accept analog and digital input, but I don't think we can program logic comparisons. To keep the costs down, my first thought was a dp transmitter. But I'm open for your idea. Do you have any suggestions about which components I could use to solve the task, so I can calculate the cost?

Thank you.

 

Much depends on the shape of the tank as the dp reading is proportional to height rather than qty whether it be large or small. From what I remember, many tanks are wrapped around the frame giving good height for the qty of fuel.

Taking gasoline at maybe .6 the density of water, and knowing that there are transmitters for 10" of water or less, full scale, you should be able to find one to read the height of fuel in the tank. The irregular shape may require that you actually physically calibrate
with fuel, but it should work. You will also need a DP cell with compatible materials as these low pressures will not take kindly to seals, etc. You may even find sensors fairly inexpensive as I have looking for low air pressures. The new generation of silicon sensors
are very reasonable. Built onto a transmitter they will be more spendy, but racing is seldom a poor man's sport anymore.

Regards
cww

 

I have uploaded a couple of pics of the tank:

http://img231.imageshack.us/img231/3681/tank1z.jpg
http://img215.imageshack.us/img215/3155/tank2ad.jpg

From what I can understand, the shape should be well fitted for hydrostatic measurement.

Do you have any suggestions about some web sites I could visit to look for suitable transmitters?

Thanks.

 

A hydrostatic DP or guage sensor provides the actual head pressure it is measuring. Meaning it only senses the column of fluid above/ acting on the sensing diaphragm. Whether there is 60 liters or 6 liters if the height is only let’s say 10” the sensor will only give a 10” of head pressure reading, again regardless of volume, (assuming a density of 1.)

So the question really is how much/high of a column of liquid will be acting on the sensor and do you know the density/specific gravity of the fuel? If the height is 10” and the Density is ;lets say .8 than you need a 0-8” WC sensor range, not 0-10”.

If the tank is an odd shape, meaning not a linear tank, like a square or vertical cylindrical shape, the relationship between level and volume will have to be corrected. If you can image a round or cylindrical tank laying horizontal, as it fills up the depth to volume relationship is not a straight forward calculation. A sensor mounted to the bottom of this tank will provide you a straight forward relationship of head pressure/depth but not a linear volume relationship, you need to profile this tank.

A simple way to profile an odd shape tank, (depending on accuracy required), is to fill the tank with a predetermined volume in intervals. Let’s say it’s a 10 liter tank, you fill the tank in 1 liter intervals and record the readings from the sensor, again at every 1 liter interval. This gives you a level to volume relationship in 1 liter increments. The smaller volume increments you use the more accurate your system will be. Depending on your data acquisition system, it may be able to linearize this relationship and provide a more overall accurate tank level system.

There are some low range “wet” gage sensors on the market, “wet” meaning they can be exposed to a liquid on the sensing side, not just a dry gas. Typically though these are in the 0-20” WCG range. I have seen a few as low as 10” WCG.
Typically DP’s that provide ranges in the single digit inches of water range are very large in size and very costly, typically greater than $900 USD range.

I see companies like GP:50 (www.gp50.com) that provide pressure transducers in ranges of 0-5” WC full scale, (Model 210) these are typically in the $700-$800 range but are much smaller than a DP or they have a gage sensor that has a 0-20” WC range that is in the $400 range (Model 211 or 311).

Hope that helps some.

 

I did a Google for "draft pressure transmitter" as these are in the range you would need and I see that Ashcroft, Rosemount and Yokogawa pop up on the first page so I would say "all the usual suspects" should have, or be able to order them. For these pressures, the diaphragms
of old school instruments might be a bit delicate for even a stock class road race bike, so I would lean towards the silicon sensors, or at least look at the shock and vibration specs. Try Cole Parmer maybe even DigiKey or Farnell. If Digikey has them they would be much cheaper as they are not an "automation" vendor.

Regards
cww

 

Just thought I should post some feedback. I have contacted more than 10 companies, but none of them have come up with a solution. One company was developing a solution especially for motorcycle gas tanks, but this won't be finished for months yet. So I am giving up for now. Must concentrate on other and more important things regarding the bike.

I would like to say thank you to all who contributed to this thread. At least, I learned a lot from what you posted.

Regards
Ole Knut Tobiassen