Hi all, I'm building a weather station and using a PT100 RTD as the variable resistor in a wheatstone bridge. I have the bridge sorted out but I'm no entirely sure what to do now with the output voltage from the bridge, how do I bring it to the op amp? And how do I determine what feedback I need from the system?

Thanks
Chris

 

You mention a 741. It is one of the oldest op amps created for an IC. It's specs are among the worst you can find. The reason this matters is stability. You are using a Cadillac of a sensor with a Model T amplifier.

The first thing you need to do is show us the schematic you are using. If you are stuck on this then my suggestion is to find a instrumentation type amplifier (not a op amp, but based off of precision op amps) and use it instead.

Other people may have better ideas.

I am guessing you are fairly new to electronics. What you need is an instrumentation amplifier, which also come in IC form. You can usually feed the low voltage signal into a DAC instead, and have it fed directly into a computer if this is your goal.

 

Well it's a college project, the whole thing will incorporate sending the various signalsto a PLC then on to a computer to be displayed on a webpage.

Here's a quick schematic I just did of the bridge we have set up at the moment

http://www.flickr.com/photos/76661617@N03/6878817593/
(Don't know why I can't put it in IMG tags)

The only op amp we've studied is the 741 and I just assume this is what will be available to us in college.

 

I recommend a TL074, or similar. There are thousands of op amps to choose from, it is an embarrassment of riches, and can make choosing one hard.

 

Take a look at the LM35 or LM34 IC. It could make your measuremnts more easy. The LM35/34 chip is cheap and quite common(easy to get)