Alright, well I just ordered the amps and the regulators, I should be able to begin testing in a few days and I'll update then on my results! Thank you for your help!

Hmmm, a higher output at 100°C is better. We probably have 2kΩ resistors around but the problem would be finding a resistor for my gain, since my gain equation is G=5+200kΩ/Rg, and I would need a gain of 12, so my Rg would be like 28.5kΩ which is tricky. We may be upgrading to a U6, but I can not be certain on that so I'll have to mock up an experiment as best as I can.

 

I did some further thought on your problem and realized that you could actually get a higher output voltage from the bridge if you went to a unsymmetrical bridge with a 12V supply, by using much larger resistors in the top of the bridge to reduce the current and dissipation in the PT100 sensor.

The simulation of that is below.
I used 2kΩ resistors in the top of the bridge to keep the PT100 dissipation about the same as with the low voltage bridge with 100Ω resistors.
And, due to the higher impedance load for the PT100, it's output is now about 200mV at a simulated 100°C, double of the low voltage bridge.
This improves the signal to noise ratio and requires a lower amp gain for the same 2.4V output.

So, if you decide to use this latest circuit, I apologize that you bought some regulators you didn't need.

View attachment 121057

 

Do have a 50kΩ or 100kΩ pot you could use for the gain resistor?
Or use some resistors you have to connect in series/parallel to get a close value?

 

I was thinking about it, and would reducing the voltage supply help

Do have a 50kΩ or 100kΩ pot you could use for the gain resistor?
Or use some resistors you have to connect in series/parallel to get a close value?

Yeah I might have some, I'll check later when I have the chance.

 

would reducing the voltage supply help

Help what?
Reducing the voltage to the bridge will lower it's output voltage also, requiring more amp gain.

 

Help what?
Reducing the voltage to the bridge will lower it's output voltage also, requiring more amp gain.

Oh sorry, I didn't think I posted that. I did the math earlier and realized that as well.

 

So the set up worked, and the noise is minimal so that's a good sign. The only thing I'm having trouble with is getting a good calibration, I did get 138.5 ohms at boiling temp and 100 ohms at freezing temp when I tested it. The problem is when I measure something like that's like 60 deg C then that voltage output will be off and therefore leading my temperature to be off. (like 2 degrees) I'd like to get within .5 a degree or less, the problem is when I try to account for the intermediate temperatures it'll make my 0 and span go off too.

Is there a certain type of regression I can do to fit the points?