On Thu, Aug 9, 2012 at 4:56 AM, IVP wrote: > Hi all, > > I've put this page together for PIClist > > http://www.piclist.com/techref/io/sensor/0-10mA_remote_lm335.htm > > This is a circuit I use for a couple of applications and it works fine > > I've made one up using just the front end (without the V-to-I > conversion, taking a 100mV/C voltage from pin14) to monitor > a heatsink > > I was expecting the front end would be fairly generic but find that > it doesn't work 'as is' if a standard dual opamp like the LM358 is > used > > In the attached diagram I've included comparison measurements > for the two opamps. The 3.185V when using the LM358 doesn't > budge. It's 0.64V x 5, so the gain is correct, but the 0.64V isn't > > An LM833 produces a similarly wayward result > > I expected to see about 1.04V at the output > > (2.94-2.73) * 5, or 20.8C @ 50mV per degC. The original > circuit is pretty close, 1.985V vs 2.000V > > How can I improve this circuit to make it more generic ? The OA which do the sum can do an x10 sum as well. The repeater after the 4K7-500-5k1 may dissapear if the resistor at the noninverting input is 10x greater than the impedance of resistor network above. As a general rule (and I didn't expect this from an experienced guy as Joe) every component ffrom a schematic should have a name. How do you expect someone will explain what he has to say by identifying the component in the way I've did? :) Merry Christmas! Vasile --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .