DaveFJ
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| posted on 5/5/09 at 10:56 AM |
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reversing logic of pressure sender
OK all you electronic magicians 
Is there a way to reverse the logic of a pressure sender? My new pressure sender supplying a secondary (switchable) input to my oil pressure gauge (so
i can monitor fuel pressure) works the wrong way round so zero pressure is full scall deflection and readout reduces as pressure increases....
so is there a simple way i can reverse the sender logic?
cheers 
Dave
"In Support of Help the Heroes" - Always
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hughpinder
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| posted on 5/5/09 at 11:52 AM |
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If its measuring volts can't you swap the + and - wires to the gauge??
Regards
Hugh
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DaveFJ
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| posted on 5/5/09 at 12:02 PM |
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problem is I am sharing the guage with my oil pressure sender so can't swap the inputs or the oil pressure will be in reverse....
have a single sensor wire coming from each sender with go to a toggle switch with a single output to the sensore connector on the guage
Dave
"In Support of Help the Heroes" - Always
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rachaeljf
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| posted on 5/5/09 at 12:37 PM |
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Why don't you source the same type sender as you already have for the oil pressure?
The are zillions of thread adapters available for such things if the bore/thread sizes don't match your fuel line tapping.
Cheers R
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DaveFJ
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| posted on 5/5/09 at 01:02 PM |
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oil px sender was sourced with the guage in America!
bought a sender at stoneliegh as an emergency to monitor px on the way home (i have fuel pressure problems)
Dave
"In Support of Help the Heroes" - Always
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02GF74
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| posted on 5/5/09 at 02:28 PM |
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quote:
Originally posted by hughpinder
If its measuring volts can't you swap the + and - wires to the gauge??
Regards
Hugh
excpet that it is not.
the oil pressure sender is effectivel ya variable resistor, much like water temp sender.
the guage supplies the power to the sender and the needle deflects due to the amount of current allowed to flow by the sender.
in short, without additional electronics to reverse the signal, no amount of wire swapping will give the required result.
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MikeRJ
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| posted on 5/5/09 at 04:19 PM |
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How accurate do you want the fuel pressure reading to be? Even if the new sender worked the same way as the original, the chances of the transfer
function being the same are slim.
Inverting a voltage or current signal is relatively easy, but inverting a resistance signal is hugely complex. However, you can probably just drive
the gauge with a voltage which would simplify things.
To get a reasonably calibrated result you need the following:
1) Voltage at the junction between the oil pressure sender and the gauge for a few different values of oil pressure (including zero). This gives the
transfer function of the original sender.
2) Resistance of the new sender at several different pressures (including zero and the normal working pressure).
Given those values it would be possible to construct a circuit to achieve your goal.
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DaveFJ
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| posted on 5/5/09 at 06:29 PM |
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to be honest i am not hugely bothered by it, it would just be nice if it worked in the correct sense. but i am a little worried about damaging the
gauge 
as it is i can see a reading and see the needle move when i loose pressure so i have what i need to help diagnose the fault..
was hoping there might be a simple way round this but if it is too complex then its not really worth the effort
cheers
Dave
"In Support of Help the Heroes" - Always
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02GF74
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| posted on 7/5/09 at 10:20 AM |
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exactly as MikeRJ says.
I had to make a circuit to use defender fuel gauges with Series fuel sender; not only was polarity reversed but operating voltage different.
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