Author Topic: DIY Measurement fuel quantity and EGT  (Read 1642 times)

Offline MJM460

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Re: DIY Measurement fuel quantity and EGT
« Reply #15 on: November 07, 2018, 10:30:34 AM »
Hi Alex, good news that nothing has broken.  It should be more satisfactory to reinstate what was originally installed, but very confusing that it does not work when reinstalled in the tank.  You probably said "Dang and blast", or perhaps something stronger!

Not an item that I am familiar with, I am used to climbing into the gas tank through a 20 inch diameter flanged man way, and having stair rungs welded on the inside to get me safely to the bottom to have a look.

The Admiral has mentioned the possibility of a faulty potentiometer, so I assume you are checking that, though I think that you said the resistance changes when you move the float.

It is surprisingly hard to convey in a drawing how the floats for level and overfill interact as they move, but presumably any interference there would allow some movement to be visible on the gauge, before it was blocked from further movement.  Certainly important to be sure they clear each other and work correctly.

A couple of thoughts.  It's hard to judge the angles when the unit is inserted in the tank, but is that blocking screw the correct side of the post holding the swinging arm?  When I rotate the picture so the fixed part is about 60 degrees, it looks like you are holding the float in the full position - it should go down with fuel consumption from there towards empty, or is it at the bottom by gravity in your picture?  And the gauge temporarily connected should indicate over the range.

Also, is the unit installed in the tank in the correct orientation at the mounting flange.  I don't know if the mounting flange is a standard five bolt SAE type with only one possible orientation.  Is there any possibility that it is inserted 180 degrees out (or some other angle) when installed in the car?

Thirdly, is there any possibility that someone previously has replaced a damaged float?  The specific gravity of LPG is only about 0.51.  I would expect the float to be solid due to the pressure, but a float made for water (SG of 1.0) can be too heavy to float in LPG, hence not rise when you fill the tank.  I have seen the wrong float fitted in industry, and they don't float in LPG.  You can weigh it and measure it to see if it has a reasonable displacement when the liquid is only 0.5, but unfortunately, only by removing it from the tank again.

I am also wondering if the wiring could be crossed so that it shows empty when it should be full, and the potentiometer orientated incorrectly some how.  Have the gears been separated and reassembled wrongly meshed?  But this seems least likely.

I am grasping at straws really, I am sure you will have thought of all those things.  I am really interested to see what you find. 

MJM460
The more I learn, the more I find that I still have to learn!

Online Admiral_dk

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Re: DIY Measurement fuel quantity and EGT
« Reply #16 on: November 07, 2018, 11:33:23 AM »
OK - I should have mentioned that many of the pots I come across actually measures correctly with a VOM, but are still more or less useless in the circuit.

Can you remove the pot without doing anything else to the tank ?
I ask because I would suggest that you turn the pot while it is connected to the rest of the car, in order to see the meter on the dashboard respond as it should.

Offline AlexS

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Re: DIY Measurement fuel quantity and EGT
« Reply #17 on: November 07, 2018, 12:47:19 PM »
Hey guys, thanks for responding and thinking along.

It is possible to remove the pot/gauge without doing anything else to the tank. There is only one way to install this pot in the float mechanism, this is shown in the image below as an example. Also when i remove the pot you can twist it, while float installed in the tank, you can see that the needle of the gauge changes. It changed for example from 10% to 90%. I have measured also the resistant, it also changed from let say 8 ohm to 90 ohm.
This gives the same results when I did earlier remove the float mechanism out of the tank, and I latterly move the float.

So yes, if I turn the pot I can see a increase on the gauge value and resistant of the pot.
Besides this, the dashboard is currently in my car not working. A previous owner has installed a second electrical system for the LPG system. No idea why. But beyond this, it does not affect the working of the pot and float system. It only indicates the LPG level and switching to petrol.

The float mechanism is mounted on the basis of four bolts. And can also be mounted in four different ways. However, I have already taken this into account for the assembly. And the gauge shows a value of 10% content instead of 90%.

When I removed the float from the tank, I put it in a container with water. After my knowledge floated sufficiently. And I saw no cracks or he felt heavy. Would the specific gravity of LPG make the difference?
Other while I would almost think that the 80% filling safety float is in the way the level float mechanism?

I try to explain the 80% safety system operation and the placement in the tank.
This safety also includes a kind of float. With a certain amount of volume in the tank, it cut off the supply. The rod of this 80% filling crosses the level float mechanism as if it were true. If the tank is empty in this case, the rod of this safety system rests on the position of the gear mechanism of the level float. If the tank is going to 80% fill, it would be lifted and thus float on the LPG liquid. However, if I look at this, the level float itself has enough space to move up and down. The float does not run into anything.
However, I can imagine that the rotation of the gears can be somewhat limited by the fact that the 80% filling system rests on these gears. But the question is how much and whether it has an influence.

I could remove the float mechanism. That is not a big deal. Maybe I should get some more information about the location of the components in the tank. Whether the rod of the 80% filling is mounted correctly. Or get the float out and compare with a new one with an LPG specialist.

Offline MJM460

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Re: DIY Measurement fuel quantity and EGT
« Reply #18 on: November 08, 2018, 10:21:24 PM »
Hi Alex, sorry I missed answering this one yesterday, I was somewhat distracted.

I see you tested the float on water.  You did not say if it floated high or low relative to the surface.

Water has a density of 1000 g/litre, and a specific gravity of 1.0

LPG has a specific gravity of 0.5, so a density of 500 g/litre.  If you float has a density of even 550 g/litre, it will easily float on water but will not float in LPG.  Unfortunately I don't have much information about the SG of plastics, but the measurements are reasonably simple if you have a digital kitchen scale.

I would suspect that if the overfill protection float is resting on the gear, the friction would also prevent the float from responding, particularly if the bouyancy is a bit borderline.

The over fill protection is to prevent you filling to near 100 % which produces very high pressure in the tank due to thermal expansion of the liquid and too small a vapour space I f there is any temperature rise after you have filled up, so you want that working.  A bit low is better than too high.

MJM460

The more I learn, the more I find that I still have to learn!

Offline AlexS

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Re: DIY Measurement fuel quantity and EGT
« Reply #19 on: November 09, 2018, 12:53:37 PM »
Thanks MJM460. I would check the system!

Offline AlexS

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Re: DIY Measurement fuel quantity and EGT
« Reply #20 on: November 09, 2018, 09:02:09 PM »
The float system is currently working again!

I had removed the level float and weighed it again. The float, however, was 16 grams and an order size of around 30 by 60 mm. That seems light enough. Also placed the float in a container with petrol. He kept on driving neatly.

Next thing I have spoken to an LPG specialist. And he indicated that the overfill protection with accompanying float should always be straight. And that this was possible that the one in my tank was bent.
So I removed the total overfill protection from the tank and bent it straight. This was firmly in the tank. The bending was easy given that it was (probably) made out of brass.
When I assembled, I noticed that the protection was stuck against the internal supply pipe when the connection was tightened. This was easily remedied by lifting the associated float in the tank so that it did not touch the gas supply pipe. This could possibly have been the cause that the overfill protection was bent before.

So install the other components and piping and go for a refueling.

Offline MJM460

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Re: DIY Measurement fuel quantity and EGT
« Reply #21 on: November 09, 2018, 09:11:54 PM »
Great to have it working again.

MJM460
The more I learn, the more I find that I still have to learn!

Offline AlexS

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Re: DIY Measurement fuel quantity and EGT
« Reply #22 on: November 09, 2018, 09:19:40 PM »
Thanks.

Did a quick test at a local gas station. Later on I will tank several times to get some data for a calibration of the senor.

I want to read the sensor analogue. Resistance has some changed. But they are higher and that would be better for the arduino, lower amperage.

Empty tank 3930 ohm.
9.1 L 4080 ohm.
24.8 L 4170 ohm.

A quick look, as expected, the resistance does not run linearly on the basis of the quantity of liters.
The next time I refuel several times until the tank is full. So that have a number of measuring points. This should give a picture of how resistance to volume is.

I am thinking of taking an average resistance per volume of gas for the total tank volume. This average resistance as value 'a' and an offset, being start value as 'b' given formula y = a.x + b.
Or I was thinking of taking this average resistance per two known calibration measuring points. As being between 0 and 9 liters, 9 and 24.8 liters, etc. But first, you need more measuring points and a reading in arduino.

Offline MJM460

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Re: DIY Measurement fuel quantity and EGT
« Reply #23 on: November 09, 2018, 11:17:21 PM »
Hi Alex, calculating the volume in a horizontal cylindrical tank as the level increases is a nice exercise for a calculus student, it is even possible to allow for the shape of the ends.  I had to do it for a large LPG tank as a young graduate engineer.  Then the circular movement of the float adds a further complexity, then the potentiometer characteristic.  Incremental filling seems the most practical procedure.

It will be interesting to see if it is close enough to linear, or if you need to use a more complex equation.  The great thing about excel is that you can get the computer to insert a trend line of almost any form once you have a number of points.  Then let the Arduino do the maths.

How are you getting a suitable input to the Arduino from the potentiometer resistance?  A reference voltage and a resistor divider perhaps?

With the float 3 cm by 6 cm, a rectangular float more than 2 cm thick will displace 18 Gm of LPG so should float if the arm is not too heavy.  If cylindrical, well you can see the maths is not too hard.  You need a float at least 32 cc, plus allowance for the arm weight.

Looks like you are making good progress.
The more I learn, the more I find that I still have to learn!

Online Admiral_dk

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Re: DIY Measurement fuel quantity and EGT
« Reply #24 on: November 11, 2018, 08:30:10 PM »
Great that you have solved the float issue and that the gauge is (kind of) working again.

The fuel meter on my bike isn't linear - but this suits me fine as most of the "movement" (LCD) is on the last quarter of the tank, where I need the resolution the most.

Offline AlexS

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Re: DIY Measurement fuel quantity and EGT
« Reply #25 on: November 13, 2018, 09:18:01 PM »
It is nice that I can now read the tank contents on the gauge at the tank. Now let's see how I can get a correct readout via arduino. I have been busy with this for the weekend.

The idea of ​​using a trent line by means of Excel is a good idea!

But I'm still playing around the potentiometer anologe readout via the arduino. In principle you read the voltage from what is on the corresponding input (Convert the analog reading to a voltage). In this case you measure the remaining voltage which is not over the sensor.

In terms of programming it is a fairly simple script. And testing through the use of a potentiometer works fine.
Only the strange thing is that this does not work if I connect an ordinary resistor or the sensor of the tank. The 5 volts are connected to one side of the resistor and the other to the analog input.
I have tried different resistances. But I get a reading of 0 volts. While a potentiometer can regulate the voltage between 0-5 volts (15kohm-0ohm).

The strange thing is that when you connect both the resistor or the senor, you can measure different voltages with a multimeter.


Maybe I'll miss something! However, I am still learning with electronics.



Script:  https://programmingelectronics.com/tutorial-09-reading-analog-pins-and-converting-the-input-to-a-voltage/

Offline MJM460

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Re: DIY Measurement fuel quantity and EGT
« Reply #26 on: November 14, 2018, 09:51:54 AM »
Hi Alex,

My knowledge of the Arduino system is pretty basic, but I am more familiar with Picaxe.  A different chip manufacturer, but might be similar enough in principal to help you find the right path.

The analogue to digital conversion on Picaxe needs a voltage input, maximum less that the actual chip supply voltage.  This may be less than the voltage to your board, as I think the Arduino boards include a voltage regulator.  On Picaxe it is 5 V Max.

To read your potentiometer you probably connected the ends of the pot to zero and five volts and the slider to the ADC input.

For your fuel gauge, I initially assumed you would use a 12V supply.  But on further thought, it would be better to use a 5 V supply so the slide always sees something between 0 and 5V.  Then connect one end of the transmitter potentiometer to the 5v, the other end to 0V, and the slider to the ADC input

I hope the similarities of the working principals of the different chip makers are enough for that to help. 

MJM460
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Online Stuart

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Re: DIY Measurement fuel quantity and EGT
« Reply #27 on: November 14, 2018, 10:00:57 AM »
Most older car fuel gauge systems used a 10vdc regulated supply , a very crude one to boot

Reason the fuel level would vary with the state of charge / alternator output

Between nominal 12.5 vdc to 14.6 vdc

Just a 2 pence worth

Stuart
My aim is for a accurate part with a good finish

Offline MJM460

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Re: DIY Measurement fuel quantity and EGT
« Reply #28 on: November 15, 2018, 10:04:54 AM »
Exactly, Stuart.  Hence my feeling that it is better to use a 5 volt regulated supply.  Easily made with a three pin chip and some condensers, then it is independent of the car operating voltage.  It can operate on any voltage above about 7 V.

Alex, I assume you know how to do this, but I can send you a circuit if you need it.

MJM460
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Offline AlexS

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Re: DIY Measurement fuel quantity and EGT
« Reply #29 on: November 15, 2018, 01:46:16 PM »
Indeed stuart. Thanks for your comment.

I'm curious about your circuit MJM460, any help is welcome ;)

Only thing is that a potentiometer has three connections.And the sensor in the tank contains two. Like as a normal resistance.

I have also seen another arduino script that works with the hx711 chip to read resistance. I used this chip before to read the load cells. The operation is in principle the same as what I have done here (5 volts through the sensor). Only now a much smaller voltage is sent and transformed into a digital signal.