Electronics > Projects, Designs, and Technical Stuff

DVMs aren't benign

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Doctorandus_P:
I think that Dave did a trouble shooting video recently of his own uCurrent.
If I remember well, a (substitute) opamp had stability issues when loaded with cables and meter impedances and started oscillating.

So, even when meauring DC, check for weird stuff with your scope.

Dave:

--- Quote from: Doctorandus_P on February 03, 2019, 09:16:09 pm ---I think that Dave did a trouble shooting video recently of his own uCurrent.
If I remember well, a (substitute) opamp had stability issues when loaded with cables and meter impedances and started oscillating.

So, even when meauring DC, check for weird stuff with your scope.

--- End quote ---
In that particular case, it was not really a problem of opamp choice, but bad circuit design.

Conrad Hoffman:
Finally got back to this and concluded that the 3478 doesn't contribute much. The shift is caused by the 3455, but I think it's just hum pickup, as properly connecting the shield reduces the error to near zero.

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