Message-ID: <01C0270C.D7BC3320@DAVE>
From: Technical Support <support@visionmicrosystems.com>
To: "'JOSCALES@aol.com'" <JOSCALES@aol.com>, "'lancair.list@olsusa.com'"
	 <lancair.list@olsusa.com>, "'support@visionmicrosystems.com'"
	 <support@visionmicrosystems.com>, "'avionics@lancair.com'"
	 <avionics@lancair.com>, "'marvkaye@olsusa.com'"
	 <marvkaye@olsusa.com>
Subject: RE: Vision Micro problems
Date: Mon, 25 Sep 2000 16:20:43 -0700
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

Hello Jim,

Thanks for copying us on your email. We are really committed in supporting our customers in any way we can and appreciate being communicated with issues that are not being resolved to your satisfaction, regardless of what the problem source may be. I will try and be as concise as possible here to hopefully address your issues. We hope this will result in mutual cooperation and your continued faith in our product and company.

The fuel probe issue is clearly one in which the EI design (a mechanical copy of our original design we did in 1989, but with their own spin on the electronics) is reported to be very susceptible to RF interference. We hear of this fuel level complaint a lot. We question the customer as follows because in many cases the customers are not aware of what fuel PROBE they have installed. First step is to see if the probe has an EXTERNAL assembly on the probe wires. If the answer to this is YES, then you have an EI probe. (The bulge is where EI has decided to place their electronics for fuel signal processing. Ours is built inside of the metal housing for extra signal repeatability, stability and immunity to RFI etc). As we don't have any information about their circuit design, we cannot officially recommend any direct methods in which to reduce their problem. Unofficially, as a gesture to try and help you with the problem, we would suggest that the entire 'bulge' be covered with a shielded wrap and grounded to the probe metal body. A product called zippertubing is a generic shielding material that is somewhat easy to work with. We stock this material and can make it available for you to try if you like. Also the use of ferrite beads on the leads etc may help as well. 

Regarding Lancairs response:
You wrote:
< After talking with Lancair about the problem, it was decided to change both
< instruments to VMI units.  We did this and saw the same problems with the new
< units.  VMI took the position that the problem was with the probes and that
< if VM probes were installed the problem may go away.  This obviously was not
< sufficient motivation to cause me to remove the wings of a finished and
< flying airplane.

Lancair was correct though in stating that this would solve the fuel level RF sensitivity problem (as builders ourselves, we can appreciate the work involved in changing the probes). Based on this, we assume that the fuel probes were not changed to the VMS units, correct ?  Once again, the VMS probes will solve this problem, but you have to be the judge as to what is the best path to take.


With respect to you writing:

< Basically, I was told by those connected with this situation that there was 
< nothing that could be done and I would have to live with it.  I disconnected 
< the warning buzzer for the EC 100 annunciator panel and "lived with it".  
< Turned out that living with it involved explaining to my passengers each time 
< the EC 100 showed WARNING:  LOW FUEL that it was just a glitch and there was 
< no real problem.  So far, to my surprise, no one has questioned my 
< explanation.

We are not sure who or in what context you were told 'you would have to live with it'. The EC100 is doing its job in reporting low fuel even though it is bad information produced by the EI probe. We can only guess that perhaps you requested that the EC100 design be modified to conditionally reject the low fuel warning. We would hope that you would understand our reluctance to do this. We sure do understand the discomfort with a false warning that has to be explained to your passengers and encourage you to take the suggested approach in solving the problem. As a side note, we actually can burn a new fuel cal chip and set the fuel level alarms to never go off. Your choice on this option. I would have been pretty sure we would have made you aware of this option, but it does permanently defeat the 'real' low fuel warning. Let us know what you would like to do?


OIL and AIR TEMP sensors:
The oil temp and air temp sensitivities are a separate technical matter from the EI fuel level probe issue.
We are aware of some instances where oil temp & air temp probes 'couple' the COM transmitter energy inside it via the cable wiring. This generally appears only on some of the composite fuselage aircraft where transmitted energy is quite high and is being radiated through the cockpit and other avionics.
You stated that the EI air temp systems also reacted when the mike was 'keyed'. We believe they use a thermocouple for a air temp sensor which is quite immune to RF, so this may indicate that you have a very high level of RF energy surrounding these sensors.  This effect is quite dependent on how the transmitted energy propagates through the airframe and how the wiring happens to route through the aircraft etc. For example, some builders report problems with autopilots (altitude hold etc.) when 'keying the mike'. Since our oil and air temp probes use the same sensor technology, both are affected in a similar manner. The software averages the values at different rates (oil temp is the longest) and hence it takes a while to return to its previous value once the mike is 'unkeyed'. (Note that no damage will occur to the oil & air temp probes during this event). We are working towards a good overall solution. These are some of our short term ideas in which to try and protect the probes against this high energy level for these aircraft. Some or all of these steps can be applied depending on the intensity of your aircraft's' radiated energy:

1) Connect the SHIELD wire of the Oil Temp Transducer cable (at the engine and DPU end of the harness) to engine ground. IMPORTANT:  Insure the engine is VERY well grounded.

2) Gently twist the exposed RED & BLACK wires that go into the sensor to form a twist every 1/2 to 3/4 inch or so. You probably will need to disconnect the harness to perform this.

3) Place RF suppressing 'ferrite beads' over the red & black wires. Slide the bead(s) down the wires so they are right next to the sensor housing. Dab a little silicon rubber on them to secure them into position. (We are looking into the what bead(s) are the best, but in general at the VHF frequencies, most of the general ferrite beads are applicable).

4) Place foil shielding over the RED & BLACK wires that are outside of the shielded cable and connect the foil to ground.

Suppressing RF fields is very dependent on many factors, so tends to be a bit of trial and error. The main idea in all of this is to prevent (or reduce) the high RF energy from being conducted inside the sensor via the wires. Please keep us in the loop' and let us know how these measures work for your application. We'll provide you with all the assistance we can.

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LML website:   http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore:   http://www.buildersbooks.com/lancair

Please send your photos and drawings to marvkaye@olsusa.com.
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