Cabling for pennycap system

kragby · #1 07-01-19, 02:24 PM

Anyone know what the cable is hooking up the sensors to the controller?
I had my 337G corrosion ACF50 treated and fuel guages quit, Assume the cabling or connections were affected capacitance wise. Anyone have any info?

JAG · #2 07-03-19, 11:06 AM

Not sure the question - are you looking for the wiring diagram, type of wire, location of wire?

were all tanks affected?

My experience with any electrical issues after someone has been inside wings, panels, etc, is that you break off a wire at a terminal or crimped connector (accidentally of course). The first thing I always trouble shoot is the circuit to ground. Often times a bad or broken ground is the culprit.
Jeff

kragby · #3 07-03-19, 12:24 PM

I found a good article on trobleshooting pennycap. It was working fine until I got ACF50 corrosion treatment when both guages went to zero. The oil is apparently somewhat conductive or it change the capacitance or some such.
The article describes that the shielded cable to the probes has to be high impedance so I'm trying to find out what that cable is - I assume a coax but not
75 or 50 ohm standard tv stuff.
I tried cleaning the connections with contact cleaner but to no avail so I am planning to replace the cables completely - just need to know what they are or what has high enough z. Article also says the resistance to ground has to be over
1 million megs so I would guess that is determined by the dialectric in the coax.

JAG · #4 07-03-19, 01:31 PM

Ok - got it. I do not have the Pennycap, and the wiring diagrams I have to do not detail out the type of coax - sorry. While I have no experience on Cessna Pennycap system, I have worked on many aircraft with capacitance type systems, and my original post regarding the ground is just as important. The only time I have seen the need for the harness/cabling to be replaced is when there is a break or physical cut in the harness not at a connection point - I would be very surprised if that is your problem.

Checking all connections for continuity and presence of shorts to ground is the first thing to check. Typically, the oil on a connector, unless so thick that it somehow provides continuity between two connection, should not impact the indication system where it takes it to Zero indication.

The cable shielding is split at each connector (pin 2) at the wing to fuselage connector, and of course at each probe connector. You want to ensure all those connections are good, with no open circuits or short to ground on center wire or shield wire. If everything went to zero, it really sounds to me like an open or short in the circuit - for what its worth. Checking all the connections is time consuming, but inexpensive troubleshooting than replacing the cables.

If all your cables check out, look at what is common to both sides as well; power source and main control monitor. Could be something else failed at the same time you had the ACF done, just by coincidence. For example, if you have power to the control monitor - is the ground okay (pin 5)?

Jeff

Kim Geyer · #5 07-03-19, 01:44 PM

There are several connector in the system which I would check first. I have the most trouble with the connectors on the wing root. take off the most forward round panel at the wing root and check the connections there. my airplanes have 2 plugs for each wing and the wires are black and yellow. the other connections are at the computer in the overhead and under the round panel on top of the wing where the probes connect. i would surely check that before I would replace the cables.
Kim