aux input sensitivity

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liv
Posts: 3
Joined: Sat Jan 11, 2014 6:56 am

aux input sensitivity

Post by liv »

Is a 50mv or less signal, for example from an ammeter shunt, too low for practical use on a 0 to 5v auxiliary input?
JimB
Posts: 76
Joined: Tue Mar 12, 2013 12:52 am

Re: aux input sensitivity

Post by JimB »

Yes it is too small. 50mv is only 1% of 5 volts. So your input would vary less than 1% of expected input range. You may also find that there is noise in the aircraft that could be a significant factor - it may be as much or more than your signal. Two possible solutions. You can put a amplifier on the 50mv source to boost it to 5 volts(such as a INA122 instrumentation amplifier) or you can use a different sensor such as a Hall Effect amp sensor available from GRT.

Jim Butcher
Europa XS N241BW
liv
Posts: 3
Joined: Sat Jan 11, 2014 6:56 am

Re: aux input sensitivity

Post by liv »

thanks.
I think I'll try the INA122 using the 4.8v from the EIS for Vs. Do you think I need a resistor or capacitor on the INA output before 3 ft of shielded leads going to EIS aux input? The shunt is on the alternator output so no negative values should be sensed. Ref and Vs- to ground. Components will be in shielded box adjacent shunt behind firewall. Anything to watch out for? Thanks for the help.
JimB
Posts: 76
Joined: Tue Mar 12, 2013 12:52 am

Re: aux input sensitivity

Post by JimB »

That should work fine. You probably won't need any filtering and I would try it first without any (always take the easy way first!). I used this amp for several years on a fuel pressure for my EIS. Do you know how to calculate Offset and Scale Factor? There is an article in the files section of the old GRT Yahoo Forum that I wrote that explains how. Or I can email it to you.

Jim Butcher
liv
Posts: 3
Joined: Sat Jan 11, 2014 6:56 am

Re: aux input sensitivity

Post by liv »

Yes, I got your article off Yahoo group.

thanks
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