JW said:
[...]
INA121PA
Try that, Its found at mouser.com, the offset voltage isn't as good
as the original but it's very close. I would say the important part of
it's operation that you need actually out spec's the original.
OK, I'll give that one a try. Should I leave pins 1 and 8 disconnected for
gain of 1? The original device didn't have these pins...
Thanks again.
You need to set the gain at max. use R around the 5K region.
There is an issue here how ever, I don't know if you have +/- supply
with reference to common? I can only assume that you do, in which case,
the REF pin needs to be on the common, not the (-) rail.
After you have done that, the device should behave like your original.
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I've just did another look at your PDF file of your meter and the
op-amp you're using.
I do think a AD743 would be more particle for you even though the
input current is alittle higher. The data sheet does
not give a warm up time and drift how ever, in your application it may
not matter.
If you want to stick with older technology that is still being used
out there for the Bifet family..
The LF355/6/7, if you employ the balance circuit they show, it'll get
you to the input offset equal to what you need how ever, you may not
even need to do this. It's also possible you may still find in some old
stock the can packages which are pin for pin compatible.
It's just a matter of how exact you want the chip to be like the
original when it comes to stability in settling time and drift. I really
don't think you'll have issues for your needs.
Personally, I would experiment with the LF355/6/7 family and see how it
does. It don't cost that much so it's not like you're losing your
shirt tail.
