At 07:18 PM 11/2/2005 +0100, you wrote:
> > why? just to buffer it into the PIC.  Although the resistor
> > will be within inches of the PIC
>
>But why 'buffer' it into the PIC? what would be the benefit over a
>straight connection (with some protection and/or filtering, but that
>will be required anyway)?

An op-amp buffer will have higher input impedance, allowing more reasonable
component values for the protection and low-pass filtering.

BTW, for protection against a shorted 2-wire transmitter, it's not
unreasonable to allow for 24VDC input voltage at relatively high current.
That will cook the precision input resistor out of tolerance quickly unless
it has a fairly high rating (or some other form of protection).

Best regards,

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