GRT Avionics

Hi all,

I have been trying to calibrate my fuel tank sensors and am running into a wall. THe set-up is as follows: RV 8, EIS 4000 into dual Hx system. Resistive float sensors, standard Van's. This is wired per instructions. Left tank is Aux3, right tank is Aux4. 3SF set to 100, 3Off to 0, sensing to +. The reading I get on the gauge is zero.

The instruction say, if it says zero, you have a wiring problem. So, I removed the right wing root fairing to expose the sender unit. WIth the wire disconnected, it has 4.8 volts. The sender unit shows 240 ohms resistance measured both to the base of the sender and the fuselage. I then took the sub D connector out of the back of the EIS. Aux 3 goes into pin 20. I verified that continuity. I checked the resistance between the sender wire and pin 25 (exciter voltage) and got 460 ohms, representing the resistor in the circuit. When I connect the wire back up, the voltage at the sender is zero.

I thought maybe this was a grounding issue, but there is no resistance (0.2 ohms on a Fluke voltmeter) between the sender unit and the airframe. I ran a clip lead from the sender to the airframe just for fun with no change.

So, I'm stumped. Anyone have any suggestions?

Regards,
Michael Wynn
RV 8 Finished, more or less
KLVK

I can stop by around noon on Wednesday, if you will be there.
Your measurements suggest that there is a high resistance in the line from 4.8 volts thru the 480 ohm resistor and on out to the sender. You're sure it's not 48K ohms? This is very odd.

Bob

I will be there. Thanks

Michael

I talked with Bob Wednesday. He asked a couple of really good questions, one of which was, are you sure that was a 470 ohm and not a 470K ohm resistor. Went back and checked. Sure enough. 470K. After diving into my panel and changing out the resistors, everything works as advertised. This would be funny if it weren't such a PITA to get to the resistors. Actually, it is funny anyway.
Thanks, Bob!

Michael Wynn
RV 8 (Almost) Finished
KLVK