Didier Juges wrote: > It took longer than I anticipated, but I have the starting point of an > adequate data logger. > > For now, I simply recorded the HP10811 heater current versus ambient > temperature in my shack over night. > > It was a little more involved than I anticipated because the temperature > variations right now are not much. > So I ended up having to use a processor with a 24 bit ADC (Texas > Instrument/Burr-Brown MSC1210Y5), a stable voltage reference (AD580) and a > precision op-amp (OP-27) to measure the voltage drop across a 1 ohm > precision wire-wound resistor (type has been long forgotten). > > The op-amp is wired as a diff-amp to amplify the signal (gain of 5 approx) > and eliminate ground differences between the microprocessor board and the > HP10811 supply board. > > I checked the microprocessor data against my HP3456 connected directly > across the 1 ohm resistor and the readings were within 0.1% of each other > over a period of > 1 hour. The weak points are most likely in the 1 ohm > resistor and to a lower extent the 4 resistors used in the diff amp (all > RLR05C metal film type, I will try to get some RNC55). I am not sure what to > do about the 1 ohm resistor, I don't have a lot of choices there at the > moment. > Ideally you should use a 4 terminal current sensing resistor and a high input impedance instrumentation amplifier. A Thomas style 4 terminal resistor in a temperature controlled oil bath would be nice, but failing that a low tempco 4 terminal resistor will suffice.
Bruce _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.