---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 01/10/12: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:41 AM - Re: Noise in damp weather (Glen Matejcek) 2. 10:23 PM - Re: Re: Capacitive Fuel Level Sensor - How do they work? (Paul Millner) ________________________________ Message 1 _____________________________________ Time: 06:41:38 AM PST US From: Glen Matejcek Subject: AeroElectric-List: Re: Noise in damp weather The part about the shriek with an applied load that is corrected by cycling the master sounds a lot like an experience I once had with a balky reverse current relay. On landing roll out, just when no one would ever be looking at the electrical gauges, the bus voltage would go way low and the avionics would start to howl. Clearly an RCR isn't the problem here, but perhaps transient very low bus voltage is... Glen Matejcek ________________________________ Message 2 _____________________________________ Time: 10:23:42 PM PST US From: Paul Millner Subject: Re: AeroElectric-List: Re: Capacitive Fuel Level Sensor - How do they work? On 1/2/2012 8:41 AM, jonlaury wrote: > Cap probes allow for fuel measurement of irregularly shaped tanks. My fuel bays in the wing change in taper, both in depth and width, in addition to the whole tank sitting at an angle (dihedral), making any kind of accurate measurement impossible over the tank range when using a linear type (float) sensor. I believe the capacitive probe will be linear over its length as well; it won't "know" about the cross sectional area of the tank at any given sensing point, just whether or not fuel is present there. The advantage may be that a long capacitive probe can extend through a tank designed such that a float type sensor, on one end or the other, will 'range out', because when one end of the tank is full, the other end is still not full, or vice versa. It's also possible, though difficult, to custom bend a capacitive probe so that there's more range (flatter slope) in greater cross-sectional areas of the tank, and less range (steeper slope) in smaller areas of the tank; that tends to linearize the output. But it's a tough thing to accomplish with high resolution. Generally, linearizing a broad range signal is a problem that's been solved many times in electronics technology with signal conditioners, even before the advent of microprocessors. Whether anyone offers such a product, beyond the full/empty adjustments Jon mentioned, I do not know. But the all-in-one EI and JPI solutions, as well as AerospaceLogic's standalone indicators offer such lindearization built into their displays. In the 80's in process instrumentation industry, there were a number of well-designed (non-interactive adjustment) signal conditioners, for under $100, that had three or four linearization adjustments across an input range. Paul ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.