REFLECTOR: GRT Ammeters

[Joe Ewen]

HI Bill,

I do not have any GRT equipment, but it sounds like you may have an issue 
with the grounds.  From your description, I am guessing you are using Hall 
Effect Current sensors.  You mention hooking your sensors to pins #4 and #5, 
if this is for 2 sensors where is the sensor ground connected?  Each analog 
input requires a input signal as well as a common connection.  Make sure the 
common (some times referred to as '-') on the sensor is also hooked up to 
your analog input instrument.  If the analog common (ground) is floating you 
can have some very unreliable readings.  Hall Effect Sensors generally scale 
pretty close and are fairly linear.

Joe


----- Original Message ----- 
From: "LAURA WALKER" <blwalker105 at sbcglobal.net>
To: <reflector at tvbf.org>
Sent: Sunday, December 09, 2007 11:51 AM
Subject: REFLECTOR: GRT Ammeters


> Hi All,
>
> Anybody else have problems with GRT's Ammeter SF and Offset settings? I 
> have two, and am using them through the EFIS analog inputs at the #4 and 
> #5 pins on the B connector. The problem is that using the factory's SF and 
> Offset settings results in either battery reading a 14 amp current draw 
> when disconnected from the bus, and the remaining battery showing a 20 amp 
> draw for just the two EFISs and the EIS running. Even when I completely 
> disconnect either battery's cables from the system, it still shows a 14 
> amp draw. I talked to Sandy, Jeff, and Carlos: they all think I made some 
> weird mistake in my wiring. I told them Aerotronics did the system...I 
> just hooked up three wires each, and yes, my 4.8V output is correct at 4.8 
> Volts.
>
> I played with the above settings, and with some slight massaging so that 
> the disconnected battery reads 0 current draw, the other one shows 2-3 
> amps for the 2 EFIS and EIS running. This seems about right to me, and as 
> I add loads, it seems to come up appropriately. When I bring both 
> batteries online, the total is split correctly. My problem is that now I 
> don't trust them to be reading correctly with the changed parameters. 
> Sandy is stymied.
>
> My instinct told me to find a clamp-on DC load meter, so through E-Bay, 
> that's what I am waiting for to arrive sometime next week.
>
> Just wondering if anyone else has experienced this problem.
>
>
> Bill Walker
>
>
> PS  I have had good luck using two of the AUX channels on the EIS with 
> fluid temp sensors to create engine compartment fire detection sensors. I 
> have one at the top of the firewall between the air inlets and one above 
> the fuel spider glassed into the engine plenum. On the EFIS they are named 
> FIRE and ENG FIRE and are assigned to B1 and B2 bar graph positions. This 
> way, with the gauges page they are invisible unless either goes above it's 
> warning parameter. They both tested fine throughout their temperature 
> ranges with the thermometer and hot water test. After flying, I will 
> adjust their warning range to about 50 degrees above their temps on a 
> warm-day, sustained high alpha climb. A manual cable-operated extinguisher 
> system from Safe-Air with the cable running the length of the overhead 
> plenum will complete the system.
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