How to Convert Kpa to Liters?

Divide the pressure by the density of the fluid and acceleration due to gravity to obtain depth. Volume is then a function of depth based upon the shape of the tank. The rest is arithmetic.

Onwards and upwards.

I didnt get you PWSlack. I am not an Engineering guy it is my request that Please answer it as simple as it could be.

Just follow #1 above.

Without knowing the shape of the tank (the forum only knows what it isn't) it couldn't be any simpler.

It have maximum range of 800Kpa. It is a Bike Fuel Tank.

So long as the density of the fuel and the shape of the tank are known, then the problem will respond to calculation. It is within the capabilities of a 14-year-old Physics and Mathematics student.

Think you're on a hiding to nowhere. The difference between empty and full is only going to be about 5kPa.

You are better off with a dip stick from now on!

Dont bother with the pressure sensor. You have a "moving target" with the wrong choice of measurement principle.

Just fill the tank up noting amount of litre's, check kpa, if kpa is 5 and you put 5 litre's in, well there you have it....1 kpa = 0.145037738 psi Specific Gravity of petrol is 737 kg/m3, then by definition a litre weights 0.737 kg; or 1.62 Lbs....

http://en.wikipedia.org/wiki/Pascal's_law

This only measures depth of fuel above the sensor, If you put it at the bottom of, say, a horizontal cylinder, the amount of fuel is not proportional to the depth.

The only way I can think to use Kpa to measure the level (volume) is with a pressure difference transmitter. And you are very correct to point out that the tank is irregular and depth may not represent volume. OP should consider other measurements and may want to look into LED indicators. Google pressure transmitters and OP will recognize some difficulties to overcome. I have no experience with the LED gauges for fuel. They seem relatively cheap and I assume with properly sealed batteries for fuel.

Maybe I'm missing something...

Won't this scheme to monitor fuel volume be wildly inaccurate unless the 'bike' is at rest, motionless and upright, and has been so for a little while?

<puzzled smiley>

It'll be wildly inaccurate anyway, trying to measure an empty-to-full range of (at most) 5kPa on an 800kPa FS instrument.

Most likely this gauge will have a tolerance of about 1% full scale. This gauge will not be able to tell the difference between a full or empty tank of fuel.

Thank you all for your replies.

Which Sensor may I use europium?

I googled for the Bike fuel gauge and I came to know that People are using pressure sensor to measure fuel level.

Using float sensor will not be correct in my case because Bike's Fuel tank has an such shape which will not allow to use float sensor.

In principle there's nothing wrong with using a pressure sensor to determine depth, it's done all the time in industry. But the sensor must have the right range. For a bike fuel tank depth I guess about 200mm, giving ~ 2kPa on water, less on petrol, SG ~ 0.85. As other posters have said, 800kPa gauge doesn't have a chance.

Also volume is only proportional to depth for a tank with constant horizontal area, otherwise it's more complicated. For a bike tank you might be able to do something near enogh if you're not fuusy about great accuracy, but I doubt it.

Coonecting the sensor via a small orifice or needle valve would damp down fluctuations caused by sloshing.

I had (many, many years ago) a '66 Triumph Trophy Twin. I knew that a full tank would get me, on average, about 200 miles. When I fueled up, I would use the grease pen I kept for the purpose and write on the tachometer glass, after wiping the old number away, the current odometer reading plus 150.

Easy-Peasy.

I do like the sight glass modification Tom offered... pretty clever! Not pretty, but quite functional. I vote GA for that.

A pressure sensor can work for this application only if it measures the pressure difference between the empty space at the top of the tank to the base of thetank. If this is the case, the formulas already given in the replies will work.

For accuracy, the sensor should measure much smaller pressures than 800 kPa again as mentioned in many of the replies.

Many MEMS based sensors for pressure of a few mm water gauge are available in the market.

Two pressure gauges working together - one at the top,of your tank, to measure vapour pressure (if different than ambient), and one at the bottom, to measure fuel weight + vapour pressure - and you have (nearly) all the info you need to compute fuel volume (you still need to know the correlation between fuel weight and fuel volume as dictated by tank geometry). Subtract the top pressure from the bottom pressure to get fuel weight. In practise this will involve outboard electronics - digital or analog, depending on how fancy you want to get - electronics which you may very well have implement yourself.

I am mentioning this as one (albeit rather complicated and expensive) approach for completeness. It is certainly possible, but other approaches mentioned here on this thread are, in my opinion, FAR superior in their simplicity, reliability and low cost. You've a pressure gauge, sure, but what about the electronics to condition the signal? How are you going scale the signal to drive a gauge, and with what? How are you going to correct for tank geometry? If you go with a digital solution will you use a lookup table and interpolate? What programming language will you use? Are you planning to low-pass-filter the difference to compensate for sloshing? As you can see, there is a lot more to it than drilling a hole and screwing in a pressure sensor. That's the easy part.

When you wade into the details a sight glass or wax pencil begins to look pretty good. If, on the other hand, you still wish to give it a shot, start by getting a pressure sensor in the right range. As others here have explained, the sensor you have now is not appropriate for your application.

Differential pressure gauge, perchance?

Functionally, yes, but your suggestion of a true differential pressure transducer is a better idea methinks.

on the scary modifications though it scores high. More fuel in the tank when you turn right.

If the bike falls onto its right side that plastic tube is going to come second in a fight with the road. Metal bits sparking, fuel flowing and Darwin takes another of his own.

I doubt anyone would be checking the fuel level while turning right...unless they were looking to do your second scenario! Not suggesting it's safe, just showing what someone has done to solve the problem at hand.

Sight tube will read low when parked on kickstand, leaning to port. The degree of an inaccurate level reading while turning will depend on the speed of the scooter, won't it? This scheme will only give a representative average of the volume of fuel in the tank. Close enough, it's a motorbike.

Compared to the inherent dangers of riding a motorcycle, this modification adds a very small fraction of concern, IMHO.

I still like it.

Scary? Nah.

Scary is when you notice the driver of that 18-wheeler in your lane is wearing contact lenses.

One might wonder what the cost of the indicator breaking would be.

Suggestions already posted to calibrate the gauge as you pour in measured quantities of fuel are along the right lines.

I did this on my boat tank. The gauge senses head pressure through a capillary tube of some length so movement and tilting of the tank has little instant effect on the reading. All fairly primitive - no Nobel Prize here for remote depth measurement - but better than running out of fuel.

Since you reported in a subsequent post: "this for bike fuel tank", we all then understand you are referring to a motorcycle with a fuel tank of approximately 2-5 gallons, yes? We certainly hope you did not mean to type: "big fuel tank", meaning large fuel tank in excess of 50,000 gallons.

Use a dip-stick or a special tank cap with the gauge built into it. Your pressure sensor will never work, since we also presume you to be working with gasoline. Even if the operating range of the pressure sensor was appropriate (which it is not), the pressure inside the tank will change when capped, depending on how it vents (or not), in addition to change in fuel level in the tank.

even if this could work tell me there will be no wires and electricity involved. A small spark and small leak and you will be history. THe temperature your engine generates is tiny compared to the temperature of a small spark - way past the ignition point of petrol.

On my old bike there used to be 2 supplies one to each carbs - one slightly higher in the tank than the other. As you run out of fuel so the bike would go from a twin to a single - enough to get you to a filling station but not something that could be easily ignored. On a bike every 100 miles you are looking for gas. Fill it then.

your existing pressure display is in Kpa actually the scale is nothing its only to give you an idea (l/bar/mbar/kg are to show you the type of result )orignally these are binary values ( ,which is getting information from a transducer which will be 0-10v or 4-20ma.

install the P-transducer to the lowest point of tank (make it empty ) and set your display (from calibration setting ) to zero gradually pour the water and (measured) and read the values .which will enable you to understand the rising curve of voltage/liter .

study the curve and increase/decrease the decimal point value as desired.

The gauge you have is inadequate for this job and cannot be safely modified to work in this job. You will have to purchase something else to do this. I like the gas cap with the built in float gauge.

We seem to see a number of these 'Fuel gauge for a moped' sort of questions... are these, in fact, school projects?

Yeesh, it's a moped or motorbike for crying out loud. Manufacturers, by and large, don't feel the vehicle needs one. Not mandated by even the USA for imported bikes.

Here's a novel idea not covered so far: ( I expect full royalties off any patent rights you obtain.)

You remember those little adhesive strips that tell temperature? This is the perfect application. Wrap the strip 2/3 of the way around the tank laterally, so that some part is over the top of the tank (important for temperature "reference"), and the remaining ends of the strip reach downward toward the bottom of the tank, cut off any extra. If the strip is applied at the point of greatest girth of the tank, somewhere near the front, then some part will be in indirect contact with liquid, and some part will be in indirect contact with vapor. Since liquid has a larger heat capacity than vapor, the strip will be cooler on segments where liquid is present, and voila, you have an instant tank gauge, as long as the sun is shining, provided the ambient temperature range is consistent with the temperature strip.

Another idea might be to try some sort of audio oscillator circuit where capacitive coupling through liquid changes the tone, but be careful with that one.

I hate to say it, but those are already pretty common on LP tanks for 'guestimating' the amount of fuel left. The whole strip is geared to the same temperature, so you look for the edge between the bright 'full' section and the dark 'empty' section.