At 03:29 PM 3/12/2004 -0500, you wrote:
>Hello All
>
>I am working on a PIC based High Voltage module. The schematic of the
>current meter portion of the module is attached. I am measuring the
>voltage drop across a knowm resistor, but to do it I had to use two
>voltage dividers to bring the levels to something I can read. I measure
>about the same current with or without a load. What could be going on?
>Loooking into the devider there are 50Meg Ohms to Ground, Is this what
>is messing up my reading?

Are you trying to measure the voltage across the 1K resistor? That's
REALLY not feasible, your whole signal will be lost by a 100ppm mismatch
between the 100M resistors, and if you wanted 10% accuracy, you'd need
them to match and track within +/-10ppm. That's just not going to happen
at that resistance level.

Howzabout you put the 10K in the TP10 to ground net and measure the
voltage across that? Add some protection in case the output gets
shorted you don't lose the op-amp etc. every time.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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