POST Issue 4 of 2016_12_06
Hi WEG,
Below is the schematic for the circuit I had in mind.
spec
CIRCUIT DESCRIPTION
(1) The differential gain of N1 is set by R5, according to the formula R5 (in K Ohms) = 49.4/(G-1), where G is the differential voltage gain of N1.
(2) The differential voltage gain of N1 is 10 with the R5 value shown.
(3) The voltage output from the LM35s is 10mV/Deg/C, which means that if the temperature of N3 is 100 Deg C higher than the temperature of N2, the output voltage of N1 will be 10V.
(4) If the temperature difference of N3 and N2 is reversed, the output of N1 will be -10V.
(5) If both N3 and N2 are at the same temperature the output from N1 will be 0V.
(6) C1, C7, C4, and C5 are decoupling capacitors
(7) R2/C3 and R3/C2 are low pass filters to minimize noise effects.
(8) R4 is an isolating resistor to keep N1 happy.
COMPONENTS
(1) All capacitors are ceramic X7R dielectric, +-10% or tighter.
(2) All resistors are 1/4 watt or higher, metal film, +- 5% or tighter, except R5 which is +-0.1% or tighter
DATASHEETS
(1)
https://www.analog.com/media/en/technical-documentation/data-sheets/AD620.pdf
(2)
https://www.ti.com/lit/ds/symlink/lm35.pdf