GP Input using Voltage

[N952W]

I have a capacitance probe that I am using for Oil Quantity on my Rotec Radial Kitfox. Can I connect the probe output (0-5VDC) to the GP3 Input rather than using a resistive probe? What would the probe type setting be?

 

[dynonsupport]

We don't support oil quantity in general, so there isn't a perfect way to do this.

The best hack I can think of is to use the elevator trim indicator or flaps indicator, which can be calibrated over whatever range you want. It will show "flaps" or "elev" though, and you can only have one per system so if you are using them already you can't display a second one.

 

[N952W]

I was planning to use the Fuel Tank 3 as the indicator. If my probe output is 0-5VDC, do I need to add a load resistor for this?

 

[dynonsupport]

No, you don't need a resistor. 0-5V into that pin will work fine. You would want to set the input type to capacitive, and you will need to calibrate it.

 

[dodsond]

Am I missing something? I thought fuel level 3 was a GP input and it was to be used only for resistive inputs, not voltage.

Do the GP inputs measure 0-5v calibrated against the units selected in the setup pages if the 5v exitation circuit is not connected? I could use this for a fuel tank 3 myself, as well as looking at the ignition advance from a Plasma III ignition.

Doug Dodson
Glasair II-S FT

 

[dynonsupport]

Sorry, you are correct.

This isn't a question with a perfect answer. Some cap-voltage senders will work fine on a GP pin. Some will not. It has to do with the way they output voltage. Only way to find out is to hook it up and see if it works. If it works, it will range from 0-5V. If it doesn't, it will probably be stuck at 5V all the time.

If you have two other cap senders in the plane, you may not be able to do it, assuming they don't work on a GP pin. If you have resistive senders in the plane, you can hook one of those to the GP pin and you cap sender to the normal fuel level inputs.

 

[dodsond]

I have 3 cap senders, all made by Vision Microsystems. I also have a converter module from Princeton that takes these probes and outputs 0-5v. The converters have their own calibration procedure so the curve will already be well linearized from full to empty.

Can I hook one of these to a GP input and call it tank 3?

Doug Dodson
Glasair II-S FT

 

[dynonsupport]

Unfortunately, probably not. But you can hook it up and try. As mentioned before, it matters if the sender can pull down against a 10K pull-up to 5V. You can call Priceton and ask, they might know. It depends on how the internal circuit works.

 

[dodsond]

I did ask this question, and Todd says it can pull down to .5v. Based on the calibration I have now on a dedicated fuel input, it looks like I get .5v at 1.5 gallons, and 0 volts at .8 gallons. So I was getting an empty reading with just under 1 gallon remaining. I can live with that being at 1.5 gallons.

So, I think I will try making that connection and do a calibration. It looks like if it doesn't work out, I just move the wire back and the current calibration is preserved.

 

[dodsond]

I connected the 0-5v output of my Princeton CP-10A fuel probe converter to the GP2 input on a D-120.  Indeed, just as Todd Stenhauer stated, I got a good calibration to .5v.  This tank is only 9 gallons, so this calibration results in getting accurate readings to 2 gallons remaining.  The indication slopes down to 0 at 1 gallon remaining.  All very usable.

This device is working very well in this application.

Doug Dodson
Glasair II-S FT

 

[dynonsupport]

Thanks for trying this and keeping us updated Doug. This will be helpful for us in the future.