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Hi Colyn – I’m measuring the signal before it goes into the Princeton converter. The square wave looks fairly clean and is the correct amplitude (5v). When I originally bench tested the probe, I taped over the holes near the head, stood it on end, and filled it with fuel. Several aluminum chips came out when I poured out the fuel after the test, presumably left over from the manufacturing process. I’m wondering if any contamination could be causing a complete or partial short between the center conductor and the outer tube. The only other possibility would appear to be some sort of failure of the electronics within the probe head. Short of pulling the wing and replacing the probe, I’m not sure what else I can do at this point.

-Adam Molny

From: Colyn Case [mailto:colyncase@earthlink.net]
Sent: Tuesday, September 04, 2012 11:17 PM
To: lml@lancaironline.net
Subject: Re: [LML] Re: Probes gone wild

Adam, are you measuring that right at the probe or is there something in the middle?

I have not had anything like this occur with my EI probes. I did however have a lot of problems with the previous (old) princeton converters. If memory serves, these convert from freq to 0-5V. The new 10-point Princeton converters have been great.

On Sep 4, 2012, at 4:18 PM, <marv@lancair.net> <marv@lancair.net> wrote:

Posted for Adam Molny <Adam@ValidationPartners.com>:

My EI fuel probes output a square wave whose frequency is proportional to
fuel level. Before installation, bench testing showed that the probes put
out 4kHz when dry and 2kHz when full. I calibrated my Dynon SkyView
accordingly. Now, at 70 hours the left probe has become unreliable. A few
weeks ago the frequencies changed to 3kHz empty and 2kHz full. I calibrated
the Dynon, but now the probe is putting out 3kHz when full.

Has anyone had similar problems? I'll have to remove the left wing to get
the probe out, so I'd like to have a plan of action first.

Thanks,
Adam Molny
Legacy N181AM
72 hours hobbs time

[We have an EI capacitive probe on our test stand and noticed that it is subject to large swings relative to temperature. Not the probe itself, but rather the oscillator module whose frequency is driven by the probe. The easiest way for me to fill our 280 gallon tank is to pull the truck out into the Florida sunshine and expose the oscillator to full sunlight... soon as it heats up the tank tops itself right off... damnedest thing you ever saw. Only problem is it won't stay full. <Marv> ]

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