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Course deviation electrical specification

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pmather

Joined: 17 Sep 2009
Posts: 33

Posted: Mon Oct 15, 2012 1:14 am Post subject: Course deviation electrical specification

Hi

 

Can anyone let me know where to find the electrical specification for the deviation signal pair to a CDI indicator as the KI206.

 

I know the deviation is: 

 

Input impedance: 1K ohms 

Deflection sensitivity: 150mV for full scale deflection.

 

What I can't find is any specification for the limits on the common mode voltage of the CDI pair.

 

Obviously the the deviation can go negative or positive driven by the +/-150mV pair of wires. I assume that these sit somewhere above aircraft ground and are not isolated but I can't find any details

 

Any help appreciated

 

Thanks

 

Peter

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henry(at)pericynthion.org
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Posted: Mon Oct 15, 2012 1:00 pm Post subject: Course deviation electrical specification

This is strictly speculation, but maybe internally it's just a moving-coil voltmeter, which would be isolated from the aircraft supply and okay with any reasonable common-mode voltage.



Henry

  On Mon, Oct 15, 2012 at 2:12 AM, Peter Mather <peter(at)mather.com (peter(at)mather.com)> wrote:

[quote]  

Hi

   

Can anyone let me know where to find the electrical specification for the deviation signal pair to a CDI indicator as the KI206.  

 

I know the deviation is:   

 

Input impedance: 1K ohms   

Deflection sensitivity: 150mV for full scale deflection.

   

What I can't find is any specification for the limits on the common mode voltage of the CDI pair.  

 

Obviously the the deviation can go negative or positive driven by the +/-150mV pair of wires. I assume that these sit somewhere above aircraft ground and are not isolated but I can't find any details  

 

Any help appreciated  

 

Thanks  

 

Peter   



   	  Quote: 	
		  



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henry(at)pericynthion.org
Guest

Posted: Mon Oct 15, 2012 5:12 pm Post subject: Course deviation electrical specification

Unfortunately I doubt there is an official generic standard anywhere.  If you're really worried you could use something like this: http://www.ti.com/lit/ds/symlink/ina149.pdf but personally (especially if this is a one-off autopilot rather than for mass production) I would just survey some common avionics and get a range of possible common-mode voltages.  



Henry



On Mon, Oct 15, 2012 at 3:51 PM, Peter Mather <peter(at)mather.com (peter(at)mather.com)> wrote:

[quote]  --> AeroElectric-List message posted by: "Peter Mather" <peter(at)mather.com (peter(at)mather.com)>

 

 Bob

 

 That is true of a conventional CDI, but not of something like the Sandel.

 This has to process the input pair electronically. I've managed to establish

 that the GNS430 uses a fixed 2.5V above ground for the CDI - and the KNS80

 uses 4.5V. I'm building an experimental autopilot so I need to know if 4.5V

 is as high as it goes or if there is some definition of the actual standard

 that needs adhering to.

 

 Any further info appreciated

 

 rgds

 

 Peter

 

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