Doh, sorry, should have guessed that. So, you've not taken into account that the tank isn't the same shape all the way up ?
Thanks, Jim From: TOM WALKER Sent: Wednesday, July 06, 2011 2:10 PM To: [email protected] Subject: Re: [Quantum Owners] Fuel resistance Ohms of the tank sender from 19 (full) to 250 (empty) This gives a linear voltage at the top of R5 (simple voltage divider) - and the circuit inverts and offsets this to the red curve at the output of the opamp. My fuel gauge (VDO Vision) is actually current driven (hence expecting a specific resistance) and I found that at 180ohm the voltage was about 4V - again, this would need trimming for a specific instrument. Choice of opamp is fairly important as you need a R-R output capability or it simple levels off at the empty end and you would never display empty on the gauge. On 6 July 2011 14:01, Jim Hearne <[email protected]> wrote: Hi Tom, Thanks for that. On the qauge plot graph, what is tank value ?, it's from 0 to 250 Thanks, Jim From: TOM WALKER Sent: Wednesday, July 06, 2011 9:39 AM To: [email protected] Subject: Re: [Quantum Owners] Fuel resistance I did it analogue. I've attached a couple of PDFs showing the cct and the output plot (do attachments work on this group?). I will need to tweak the resistor values once I've done my measurements. I didn't get a chance this weekend as I spent all weekend pulling the dashboard out of my SEAT to get at the air-con evaporator, only to discover that the expansion valve is on the engine side of the bulkhead. Bloomin thing still doesn't work and has foxed the "expert" from Jack-Frost too. Anyway... The diodes and resistors in the box at the bottom are for bending the curve if the requirement is non linear and can be removed - although they effect the gain so R2, R6 and R7 would need to be changed to compensate. Some caps should be added on feedback to give a low pass as well - but the basic concept is there. On 1 July 2011 12:09, Jim Hearne <[email protected]> wrote: Oops. Have you done circuit with a micro or purely analog ? Could i have a look at the circuit, just out of curiosity, i've done mine with a PIC micro but then i'm much happier with digital rather than analog electronics. You are probably right about not needing every litre, probably every 5 would be fine but it's always nice having more data than you need. Thanks, Jim From: TOM WALKER Sent: Friday, July 01, 2011 11:36 AM To: [email protected] Subject: Re: [Quantum Owners] Fuel resistance Due to filling my diesel tin-top to the brim with unleaded (DOH!) I have 50 litres of unleaded in the garage, so if I get a minute over this weekend I will do the measurement. A quiet day at work this morning means I have designed the circuit - I've even put in some feedback which allows me to squash and pull the curve if the ohms/litre is not a linear scale. btw. a 2011 Passat CC diesel will actually run on unleaded - but not very nicely (I got it 9 miles home). It smelt very bad and got awfully hot. Good job I only have to keep my company cars for 6 months - some poor soul will buy that off a VW forecourt as "nearly new". On 1 July 2011 11:23, Jim Hearne <[email protected]> wrote: Sounds similar to mine, needs inverting for a start. I need to round up enough jerry cans to fill with fuel to fill the tank. I had though of doing it on the car in a petrol station at a quiet time but they might get a bit funny about that i guess. Or, i could just use water and try and factor in the difference in the sender resistance caused by the water, about 20 ohms on the empty reading. Hmm, another project to do. Jim From: TOM WALKER Sent: Friday, July 01, 2011 9:29 AM To: [email protected] Subject: Re: [Quantum Owners] Fuel resistance Thanks for that Martin - looks like I will be converting that like Jim is. My VDO expects 10ohm empty and 180ohm full. Jim - I would be very interested in getting some litre by litre values as that was going to be my next step too (although I was going to do a couple of litres at a time). On 30 June 2011 22:42, Susan and Martin Scott <[email protected]> wrote: Hi Tom Empty 247.5 - 253 Ohms Full 18.4 - 19.7 Ohms Hope that helps, Martin ----- Original Message ----- From: Tom Walker To: [email protected] Sent: Thursday, June 30, 2011 10:17 PM Subject: [Quantum Owners] Fuel resistance Does anybody know the full/empty resistances of the XR2 fuel level sender? After 5 years of collecting dust, I’m finally playing around with changing my dials. Tom -------------------------------------------------------------- No virus found in this message. 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