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Basic op amp instrumentation
I posted this to alt.engineering without much success. Perhaps someone here
can help. I am looking for an article or short description of a general purpose instrument conditioning circuit. When I was taking my electronics classes (early 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 741'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. 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, hopefully it should be a common task :-) --- 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 window as needed. I believe I once had a circuit to do this that had 3 or 4 resisters and a 2n2222. I think the circuit had the bonus of single rail power too; perhaps 12-15V. Thanks for the help! JZ |
#2
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Basic op amp instrumentation
...to buffer many sensor lights with varing voltage trip points (and
scales). 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. JZ If you want better help, stop asking how you can do something when you've *already figured it all out except the details*. 1) Give a better idea of *exactly* what you're trying to do. 2) Give some specifications--temperature range as a minumum. Having said that, thermocouples are probably a terrible way to do this. (You're already aware of one big problem.) Here's another: http://www.google.com/search?&q=ther...ment+reference Look into thermisters. |
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