First question - What is this resistor network doing? Answered that it's linearizing the thermistor but this isn't what I was looking for. I'm looking for an explanation that describes the relationship between the resistors and the output
Edit (June 23 2015) for Question #2:
I'm doing calculations on the beginning resistor circuit and something's not making sense. I need help calculating or an equation which will give me the voltage for Vout.
Here are the numbers I've been using.
- V+ = 12V
- RA, RB, RC, Rd = 15kohm for simplicity I'm using all the same amount
- Rth (multiple data) = 15k, 9.6k, 2k, 39k
I took measurements from the RA,RB,Rth node (#1) and RB,RC,RD node (#2) and the Rth,RD (Vout #3) node.
- Rth = 15k -> #1 = 7.5, #2 = 4.5 and #3 = 6V.
- Rthh = 9.6k -> #1 = 7.4, #2 = 4.6 and #3 = 6.3V.
- Rth = 2k -> #1 = 7.2, #2 = 4.8 and #3 = 6.9V.
- Rth = 39k -> #1 = 7.64, #2 = 4.36 and #3 = 5.24V.
I understand #1 + #2 = V+. But if I do voltage division for #3, it doesn't give me the correct voltage. I'm assuming because Rc is coming into play with Rd (parallel?) but I'm not 100% sure. I've been told the only reason #1+#2 = V+ is because Ra = Rc. I came to that conclusion because I'm trying to find the relationship between all of the resistors.
What am I missing?
Overall circuit task: I am trying to put 12V into the circuit and get 1-5V out of the opamp depending on the amount of light the Thermopile picks up for an outside application. So the temperature could be 30F to 110F (0C-43C).