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Fuel Pressure Indication setup HXr EFIS

Postby glk0346 » Mon Jan 07, 2019 3:12 am

Is there a different Set-up and configuration for a fuel pressure sender wired directly to a HXr EFIS versus wiring directly to the EFIS as put forth in the VDO Supplemental for the EIS, e.g. scale factor, Aux Off, etc.?

I ask this question because i have a VDO 0-30 psi Pressure Sender wired directly to my HXr via an Analog function and configured as per the supplemental and the Configuration and Set-up Guide for the HX, HS, WS EFISs and pull-up resister ON.

With this configuration, I get 47.4 psi with my system powered up, eng not running. With just the Boost Pump on and or the eng running I get no discernible chg in my reading.

I've reread the HXr Install Manual, the HX, HS, WS Set-up Guide, and delved in depth to the GRT web site with no solution.

Any help and or advice would be greatly appreciated.

George
glk0346
 
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Location: Huntsville Executive Airport, Meridianville, AL

Re: Fuel Pressure Indication setup HXr EFIS

Postby Bobturner » Mon Jan 07, 2019 6:06 am

As shown in the EIS - vdo supplement, you need a bias resistor around a few hundred ohms. The internal pull up resistor in the HXr et al is like 10,000 ohms. Try turning off the internal pull up, and supply an external 470 ohm bias resistor off the 5 volt supply, as shown in the supplement.
Bobturner
 
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Re: Fuel Pressure Indication setup HXr EFIS

Postby glk0346 » Wed Jan 09, 2019 3:01 pm

Thanks, Bob.

I'll have to use a 200 Ohm resistor instead in that normal fuel pressure for an O-320 is 4-6, with 8 being the max.

George
glk0346
 
Posts: 24
Joined: Wed Jun 06, 2018 3:51 am
Location: Huntsville Executive Airport, Meridianville, AL

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