healeys
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RE: Ammeters

To: "'Alan F Cross'" <alanx@proaxis.demon.co.uk>, <BillHUCK@aol.com>
Subject: RE: Ammeters
From: "Alex" <alexmm@adelphia.net>
Date: Mon, 19 Apr 2004 14:48:00 -0400
Haven't seen the "Just Brits" schematic yet (the link as given doesn't work
for me), but my ammeter circuit (using an Allegro Semiconductor Hall-effect
sensor chip) also requires an outboard amplifier. The one I configured uses
an op-amp, so that gain and offset can be adjusted. However, you must
account for parameter drift due to temperature, and also voltage changes on
the -12-V line in the car.

That's why I chose a MIL-spec op-amp with a -55 degree C to +125 degree C
operational range, and a stiff monolithic voltage regulator chip as well.

Even those ICs don't ensure thermal stability, only IC survival.

That's why I ultimately went with an old fashioned zero-center ammeter.

 ==  Alex in Maine
     1960 BT7 "Blue Mainie"
     Former owner 1957 100-6, 1967 BJ8
     Amateur Radio AI2Q
     http://users.adelphia.net/~alexmm/ai2q.htm

      .-.-.



-----Original Message-----
From: owner-healeys@autox.team.net
[mailto:owner-healeys@autox.team.net]On Behalf Of Alan F Cross
Sent: Monday, April 19, 2004 1:02 PM
To: BillHUCK@aol.com
Cc: happolk@cox.net; healeys@autox.team.net
Subject: Re: Ammeters


In message <51.3d78e8d8.2db539d2@aol.com>, BillHUCK@aol.com writes
>I have a problem with the concept of automotive ammeters.
>
>Should anything go wrong with the shunt, all power shuts off.
>Is that shunt not just one more link to possible failure?          Bill
Huck
>

Been watching this thread with some interest. I too have thought about
adding an ammeter, but don't want to cut into the loom or route the
entire current supply through a small meter with shunt.

But ...





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