Dual monitoring of tank level

[scaarup]

Hi all.

I have an old vdo tank level gauge and transducer. Based on resistance 0 ohm = 0% and 180 ohm = 100%.
Now I want this data on my NMEA network as well, so I bought this multimeter/nmea gateway (Alba-combi). The problem is having two devices measuring resistance. So I figured if the Alba-Combi could measure the voltage in stead. I already did some calibrations - like 2V is empty and 6V full. But is this a reliable solution?

Thanks

[RaymondR]

The problem with using voltage is that any change in connection resistance de-calibrates the instrument circuit. To avoid this problem industrial systems use a current system using 4 ma as zero and 16 ma as 100%. The current is then put across a precision resistor at the readout to produce a voltage.

[scaarup]

Originally Posted by RaymondR

The problem with using voltage is that any change in connection resistance de-calibrates the instrument circuit. To avoid this problem industrial systems use a current system using 4 ma as zero and 16 ma as 100%. The current is then put across a precision resistor at the readout to produce a voltage.

Thanks Raymond.

Do you think it is likely there will be a change in connection resistance, like you're saying? Because if not, then the voltage calibration should be reliable?

[RaymondR]

Originally Posted by scaarup

Thanks Raymond.

Do you think it is likely there will be a change in connection resistance, like you're saying? Because if not, then the voltage calibration should be reliable?

My boat came with two tank level read outs which work on varying the voltage to indicate tank levels. One appears to be OK and gives an accurate indication. The second it out of calibration which will either be a bad connections (most likely) or the moving coil meter going out of calibration.

I'll get around to fixing the un-calibrated unit one day and am quiet happy with the varying voltage systems, they are simple systems and generally fairly reliable.