VDO tubular fuel level sensor

[onthebeach7350]

Hello,

I do have a VDO tubular fuel level sensor ref. 224-011-000-250G which I need to connect to the RCP3.

As i'm a newbie in that stuff, I need your help .

This sensor has two connections points: one for the ground and another for the signal.
I attach a picture of this.

The signal returns a value in ohms.
This variates from 3 ohms (full) to 90 ohms (empty) according to the fuel level.

My question is thus simple: How do I connect this sensor to an analog port of the RCP3 ?

Thanks for your help !

[MikeD]

Look at the temperature sensor description area following this link which uses the same principle as your fuel level sender... yours is one that could be called LOW RESISTANCE GAUGE TYPE SENSOR.
https://wiki.autosportlabs.com/RaceCapturePro_Sensors

Connect the signal wire to whatever AnalogIn of your choice, and connect a pull-up resistor of 220 ohm (anything from 150 to 330 ohm may work well in your case) with one end to the same AnalogIn and the other end of the resistor to 5V sensor supply of the RCP.
I recommend 0.5 - 1 watt metal film resistors, even though 0.25 watt would also be fine.

For the ground wire it depends on the construction of the fuel cell... the best (good accuracy) would be to use the ground wire from RCP and connect this same wire to the fuel level sensor ground. However if the fuel cell by itself is already grounded (for example if it's made of aluminium or such and therefore provides a ground through the fixing screws to the fuel level sender) then you may better NOT connect another wire from the fuel cell to the RCP ground wire, as this would generate a kind of ground loop, which should be avoided as much as possible.
Therefore if the fuel level sender is grounded by it's fixing screws from the fuel cell then you should be fine when only connecting the signal wire as written above. If you are unsure about the grounding of the sender you may connect a ground wire from near the fuel cell to one of the bolts of the level sensor and will also be fine.

Come back with your results or questions in case you need further help!
-Mike

[onthebeach7350]

Thanks Mike for your detailed reply.

a few more newbie questions

What is pull up resistor?
Would a simple resistor not work?

You recommend 0.5 - 1 watt metal film resistors, even though 0.25 watt would also be fine.
What is that? What do I have to take car about that?

Update: I have checked at www.conrad.fr, they can supply regular resistance (no mention of pull up resistance?) of 220 ohm in 0.25W, 0,5 or 1W. Which one should I choose?

The fuel tank is an ATL FT3 tank.
It is not explicitly grounded. There are however some aluminium supports that are supporting the tank on a painted metal panel in the car (see picture). There are NO bolts which touch directly some metal part of the car.
Do you advise me then to ground the sensor to the RCP ground pole?

Its there an easy way to measure a parameter in order to be sure of the correct grounding solution?

Regards.

[dewittpayne]

Pull-up is not a type of resistor, it's the function of the resistor in the circuit, so yes, any resistor with the correct resistance will work. You want to apply a relatively constant current to the device so that the measured voltage at the device is approximately linearly proportional to the resistance of the device. That means the resistor from the power supply needs to be larger than the maximum resistance of the device. It also needs to be larger to limit the current through the device. If you applied 5V to the device, you would have a current of 5/3 amperes when the tank was full. With a 220 resistor in the circuit, the maximum current would be 5/223 amperes.

[MikeD]

Hey onthebeach7350,

as dewittpayne explained you can take a "regular" resistor, as Pullup is just the description of how it is used... in your case the resistor will "pull" the signal level up to the 5V line, which generates a voltage divider so that you (the RCP) can measure a varying voltage depending on the changing resistance of your sensor.

conclusion: buy a 220 Ohm resistor with 1 Watt if available, otherwise the smaller 0.5 watt version would also be working fine.
The bigger wattage of the resistor means it is physically a little more robust (and electrically it can absorb more heat, in simple terms, which would help if you accidentially have a short to 12V or such).

grounding: you could use a multimeter and measure the resistance between the mounted sensor housing and vehicle ground to get an idea whether or not you have a GND connection.
However from your description and the pic attached I would probably ground the fuel level sensor housing by wiring it to the same grounding point as the RCP and you will be fine.


BTW I've recognized that you are from Belgium and competing in the 24h series?! Great!
What car are you running?

I've three customers competing in the Creventic 24h series too... various cars, and they all have loads of CAN bus data also transmitted to their pit crews and some sophisticated calculations going on in the background for fuel management und such...

PM within this forum sadly does not work good for me so you may drop a message via the www link down below in case you need some more help.

[onthebeach7350]

Thanks for your help.

I will test with a 220 ohms and let you know the results !

Mike, we race indeed in the TCES series with a Peugeot 308.
You can check our facebook page: Semspeed
If you are on the racetrack of one TCES race, you are welcome !