On 3 Sep 2019, at 1:59 PM, Don Weigt <dweigt47@...> wrote:
Looking at the programming track waveforms, they look good. Quite square (fast rise and fall times) and nearly 12V for the positive parts and near 1V for the negative, with no load. Slightly higher low voltages and lower high voltages with a Lenz LE103, and slightly less again with the Econami. About 11V and 1.5V with the Econami. (It's a little hard to read closely on my old analog scope.) The difference between the two rails seems to be nearly 10V. one going higher when the other goes lower.
DCC waveforms should be symmetrical bipolar with always around 12-14V between positive and negative.
It's usual for one rail to go to ground at a time and the other to +12-14V at the same time So for this reason you shouldn't connect a normal CRO probe with ground clip across both wires, unless your CRO is fully floating. A differential input probe pair is preferred, or you can connect the ground clips to DCC system ground and use two channels (that's what I do with my old analog CRO). I also use a DSO adaptor on my iPad, which means my inputs are fully floating.
For typical waveforms, see NMRA S9.1 (on the NMRA website).
Dave in Australia
