Hi,
I have several questions regarding the schematic of thermistor temperature transducer application you proposed in SLOA052.
First of all, you wrote on page 4 that the gain of the U1b opamp is m = Rf/Rg +1 . I don't agree with you.
It would be the case if Vref equals 0. It's not true here. So you have here : Vout = V+ .(Rf+Rg) / Rg - Vref.Rf/Rg where V+ equals : Vthermistor+ Vr3.
Can you explain me this ?
Second question : I don't understand why you need Vref with all the circuitry around it (U1a + R1+ current source) ? Im afraid I don't understand what's the role playing
by Vref here. You mentioned (p4) :" The higher reference voltage causes the output to move closer to the negative rail at the 100°C point" .
As far as Im concerned, I would put Vref to ground and suppress all this circuitry (Vref, R1+ opamp).
Can you please be more precise ? Im afraid I don't get it why you need to produce a VREF here.
Thanks in adavance.
Younes GHANEM
