throbscottle
Well-Known Member
Okay, so I've worked out most of how my dmm is going to work now (with some help, thanks folks!), but I'm trying to understand ohms converter circuits from the couple I've found on the web. What I'm seeing is a constant current source connected to an op-amp's inverting i/p, nfb via a fixed resistance, a reference resistor (the dmm's input ladder) connected from it's o/p to non-inverting i/p, and the dut goes between the non-inverting i/p and ground. The adc is connected across the dut (or to a further op-amp connected to the same point)
It looks like a modified Howland current pump, and I understand that a constant current will produce a voltage proportional to the resistance, but I don't really understand what is going on in this circuit. Can anyone give an explanation? Also, this is now quite an old method - are things done differently in modern meters? I'm looking to produce something very stable, in the long run.
It looks like a modified Howland current pump, and I understand that a constant current will produce a voltage proportional to the resistance, but I don't really understand what is going on in this circuit. Can anyone give an explanation? Also, this is now quite an old method - are things done differently in modern meters? I'm looking to produce something very stable, in the long run.