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Resistance fuel senders to 2 gauges

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peter(at)sportingaero.com
Guest

Posted: Thu Jun 28, 2012 2:15 pm Post subject: Resistance fuel senders to 2 gauges

Guys,



I've recently re-built my panel and added an EFIS, updated the radios, 

taken out the Expbus2 and included an endurance bus. As I already had a 

pair of fuel gauges I thought I would retain them to avoid booting the 

EFIS when I wanted to find out how much fuel is loaded before flight. I 

have regular resistance fuel senders and wired the gauges in parallel 

with the EFIS. I should have realised that the apparent resistance now 

seen by the fuel gauges has decreased, so their reading decreases when 

the EFIS is switched on. This isn't a problem for the EFIS as I can 

calibrate them accordingly. But it would be good if the fuel gauges were 

more accurate when the EFIS is on.



So my question is, is there a straight forward way to share a resistance 

sender with 2 gauges without impacting the calibration of either gauge?



Peter

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 28, 2012 6:53 pm Post subject: Resistance fuel senders to 2 gauges

At 05:13 PM 6/28/2012, you wrote:


<peter(at)sportingaero.com>



Guys,



I've recently re-built my panel and added an EFIS, updated the 

radios, taken out the Expbus2 and included an endurance bus. As I 

already had a pair of fuel gauges I thought I would retain them to 

avoid booting the EFIS when I wanted to find out how much fuel is 

loaded before flight. I have regular resistance fuel senders and 

wired the gauges in parallel with the EFIS. I should have realised 

that the apparent resistance now seen by the fuel gauges has 

decreased, so their reading decreases when the EFIS is switched on. 

This isn't a problem for the EFIS as I can calibrate them 

accordingly. But it would be good if the fuel gauges were more 

accurate when the EFIS is on.



So my question is, is there a straight forward way to share a 

resistance sender with 2 gauges without impacting the calibration of 

either gauge?



   Variable resistor transducers must be "powered up"

   by their mated instrument. When you tie two resistance

   measurement instruments onto the same sensor, their

   "power up biases" add together and upsets the readings

   of both.



   What you'll need to do is tell the EFIS to work on

   a variable VOLTAGE input and turn off it's internal

   excitation of the remote sensor. Then allow the

   original instrument to POWER the transducer. Finally

   teach the EFIS how to read it.



   Bob . . .

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racerjerry

Joined: 15 Dec 2009
Posts: 202
Location: Deer Park, NY

Posted: Sat Jun 30, 2012 2:46 am Post subject: Re: Resistance fuel senders to 2 gauges

DPDT toggle switch from sender?

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_________________
Jerry King

peter(at)sportingaero.com
Guest

Posted: Sun Jul 01, 2012 2:21 pm Post subject: Resistance fuel senders to 2 gauges

Of course, the large assumption I made was that the EFIS and the fuel 

gauges operate at the same voltage - which they do not ... So now I have 

a pair of u/s fuel gauging circuits within the EFIS which will have to 

be returned to the manufacturer for repair.



I guess the moral is when you think you are being really smart, you have 

probably missed something and are about to be really dumb.



Peter



On 29/06/2012 03:50, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>



 At 05:13 PM 6/28/2012, you wrote:

 

 <peter(at)sportingaero.com>



 Guys,



 I've recently re-built my panel and added an EFIS, updated the radios, 

 taken out the Expbus2 and included an endurance bus. As I already had 

 a pair of fuel gauges I thought I would retain them to avoid booting 

 the EFIS when I wanted to find out how much fuel is loaded before 

 flight. I have regular resistance fuel senders and wired the gauges in 

 parallel with the EFIS. I should have realised that the apparent 

 resistance now seen by the fuel gauges has decreased, so their reading 

 decreases when the EFIS is switched on. This isn't a problem for the 

 EFIS as I can calibrate them accordingly. But it would be good if the 

 fuel gauges were more accurate when the EFIS is on.



 So my question is, is there a straight forward way to share a 

 resistance sender with 2 gauges without impacting the calibration of 

 either gauge?



   Variable resistor transducers must be "powered up"

   by their mated instrument. When you tie two resistance

   measurement instruments onto the same sensor, their

   "power up biases" add together and upsets the readings

   of both.



   What you'll need to do is tell the EFIS to work on

   a variable VOLTAGE input and turn off it's internal

   excitation of the remote sensor. Then allow the

   original instrument to POWER the transducer. Finally

   teach the EFIS how to read it.



   Bob . . .

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millner(at)me.com
Guest

Posted: Sun Jul 01, 2012 7:48 pm Post subject: Resistance fuel senders to 2 gauges

>> DPDT toggle switch from sender?



Probably not very good human factors to get used to looking at a fuel 

gage that reads "empty" as being normal...



Paul

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