oal100

yes yoúre right. but it may oscillate depending on the config. did you see the offset always dampening over a longer period (e.g. 60mins - with no input signal) and being stable or the opposite? the freq around a zero-offset may well be 1/300 Hz or smaller so its hard to see that the amplitude is in fact getting bigger? it sounds to me like getting sea-sick but slowly. therefore i wonder how to measure and falsify this hypothesis...

if I understand the schematic correctly, the opa445 acts as an integrator. Could it be that if the parts are well matched - and the opa445 is not in - there is a steady decline of the offset? Which in turn would mean, that the opa would correct all the time in the same direction with a declining rate? And thus overshoot? Therefore the whole system would start to swing slowly but instigates over time even to V+? How would one have to measure the amp with an open loop to get at the bode diagram? Would a bode diagram help to find out if the system - in that particular constellation - is getting unstable? Because maybe someone could post it?