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Lighting and other non-DCC devices.

Which is what I said in the part you snipped.

Not correct read the spec. In order to keep the average level at zero, if +ve stretched bits are in use then the period of the -ve part of the

0 data bits are extended so as to average the DC back to zero between stretched bits, that is why 0's are allowed to have different length -ve and +ve transitions. However, to the motor the fast -ve bits are are not seen as well due to the Low pass characteristics of the motor, so the motor sees a net +ve (or everything the other way around if you are reversing and using -ve stretched bits).

Jeff

Reply to
Jeff
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It was not me, I have never said that DCC is DC, that is how this whole argument started.

Jeff

Reply to
Jeff

Totally wrong.

Look at the picture in the spec you seem not to have read for yourself. The positive and negative portions of the stretched zero are markedly different. That's how a DC bias in imparted to the DCC waveform to drive an unchipped loco. A "stretched 0" is one which *by definition* has unequal mark/space ratio.

MBQ

Reply to
manatbandq

It thinks its been agreed that it is not AC as most people understand and for that matter DVM or MC meters, it but modulated DC that is like AC. Therefore you need meter that reads modulated DC.

Admittedly wrong about the bit stretching, a long time since I looked at and just thought +ve was 1 and -ve was 0.

From the view point of a DC motor in zero stretching it is enough DC like to make it work.

Anyway this thread has proved most interesting reading and brought back a lot of AC theory I studied many years ago at college.

Reply to
Chris

No. It's AC, end of.

You need a meter that reads "true RMS" AC instead of a cheap hobbyist meter that is only calibrated for 50/60Hz sine waves.

MBQ

Reply to
manatbandq

It's even more fundamental than that, a meter is pretty useless in measuring anything on a DCC waveform other than its presence or not. An oscilloscope or logic analyser is required to make any sense of what is going on.

Jeff

Reply to
Jeff

That would work if the waveform was "true RMS" AC rather than a DCC signal.

Reply to
Chris

There's no such thing as "true RMS" AC.

The term "true RMS" is describing the fact that the meter is capable of measuring the RMS value of any arbitrary waveform, unlike cheap meters which approximate it but are designed to be reasonably accurate for a 50/60Hz sine wave.

Since DCC is AC, a true RMS meter will give an accurate voltage measurement.

MBQ

Reply to
manatbandq

Correct in as much as it will give the RMS value over the sampling period of the meter, but if the mark-space ratios of the DCC signals vary over time the reading will fluctuate. Also bear in mind that the bandwidth of many DVM's is quite limited and will not give an accurate reading on a square wave with fast edges, even if the fundamental frequency is with its range.

Jeff

Reply to
Jeff

Which is what I was alluding to, very well put. Probably more true for moving coil meters.

Reply to
Chris

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