Instrument Opp Amp Design

I am looking for an article or short description of a general purpose Instrument condition circuit.

When I was taking my electronics classes (1980's) I recall a diagram that showed an opp amp that had +- offset and variable amplification. I have looked in my library and all I can find is specific applications. The references I have are all too complicated... i.e. temperature compensation etc.

I am hoping to have a fairly crude circuit that will use 749's or something with perhaps just two or three other components to buffer many sensor lights with varing voltage trip points (and scales). I would like to use one circuit many times over with predictable component values.

Thanks for the help!

JZ

Reply to
<jwzumwalt
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on 01/04/2004, snipped-for-privacy@hotmail.com supposed :

From what you have said, you need to look at op-amp comparator circuits. At a preset level of input, the output flips over. Using the op-amp, you compare the input against known fixed and stable voltage reference and as it crosses the set point the output changes to the opposite polarity.

Reply to
Harry Bloomfield

Thank you for your suggestions and reply.

The problem with a simple comparator is that most sensors have too small a voltage difference - hence the need for the settable amplifier.

For example, a thermocouple may only differ by a few millivolts from "cold" to trip point. Therefore it is necessary to expand the sensitivity "window" to a couple volts.

Suppose the full response of a sensor is 15mv (i.e. 75mv-90mv), if we amplify it 200x then we have a 3v difference. Typically we would like the trip point at some standard value such 6V so we offset the 3v as needed.

I believe I once had a circuit to do this that had 3 or 4 resisters and a

2n2222. I believe the circuit I had used single rail power too; perhaps 12-15V.

I just moved from Alaska to Seattle and I looked through all my references as I packed but to no avail. I was hoping that someone on this list was involved in instrumentation, it should be a common task :-)

JZ

Reply to
<jwzumwalt

Maybe this will help:

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Ben Miller

Reply to
Ben Miller

Thanks for the help, this has information that I can make work, I was hoping for a bit more basic real world example and computations :-)

Thanks again Ben, this now gives me some workable options!

JZ

compensation

Reply to
<jwzumwalt

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