The traditional BNC only has two connections (signal and shield), so for the BNC Adapter Board the negative input is tied to ground/shield and the scope input becomes single ended. Such differential setup requires 3 connections: positive, negative and ground. Hi Analog Discovery Scope inputs are fully differential but not floating. It has certain limitations to the ground of the device, so a ground connection toward the circuit under test is needed. oscilloscope channels with isolated grounds. I offer the Tektronix THS720 oscilloscope as a particular counterexample, and the Tektronix Application Note "Fundamentals of Floating Measurements and Isolated Input Oscilloscopes Application Note" as a general counterexample.įrom my perspective, it's much more desirable to have a versatile instrument that maintains its differential channels all the way through: you can easily reconfigure them to have a common ground by tying their "-" inputs together taking channels with a common ground and making them differential is a much uglier problem, as highlighted by the other posters in this thread.ĭug into this topic when a Hackaday article elicited a discussion in its comments of oscilloscope channels with common grounds vs. Hello you kindly cite a source for your above statement "BNC is 'by definition' single ended", please? At least that would give the user a choice about whether to operate as differential or single ended inputs. You could also provide jumpers to select single ended behaviour instead, by shorting the negative inputs to ground. Then the Discovery BNC adapter board could be used for fully differential measurements. IMO it would be better to provide 4 sockets for scope probes, with each connected to one of the differential inputs, and all the scope shields returned to Analog Discovery ground. However, if you're going to do this you should at least warn users about what you've done. I can see that grounding the negative inputs could make sense, in that it makes the analog inputs behave more like a conventional oscilloscope, where the probe shields are usually returned to Earth. I was lucky, but providing users with a warning about this could save somebody's life one day. Users should be warned in BIG LETTERS about this change in behaviour, perhaps printed on the PCB as well. IMO this is a safety hazard, because adding the Discovery BNC adapter board to the Analog Discovery changes its electrical behaviour in a significant way (from differential to single ended) but there is no mention of this in the Discovery BNC adapter board reference manual. Instead, there was a crack, a flash, and a little jet of molten metal, as the clip on one of my scope probes vaporised! I was expecting each channel to measure the differential voltage across each probe. Why is this important? I just found out the hard way, when I connected the scope leads from the Discovery BNC adapter board to parts of a circuit at very different voltages. Therefore, they form a short circuit between any conductors they are connected to. Although the Analog Discovery has fully differential analog (scope) inputs, the Discovery BNC adapter board does NOT! For some reason the negative inputs of both analog channels have been connected to the Analog Discovery ground.
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