Re: PC based storage oscilloscope
Vollrath, Don <dvollrath@...>
An interesting problem indeed. You described an ideal use for a miniature DC coupled clamp-on hall effect type current probe. I have borrowed one on occasion to help diagnose other current related issues.
From: WiringForDCC@... [mailto:WiringForDCC@...]
Sent: Friday, November 13, 2015 9:05 AM
Subject: RE: [WiringForDCC] PC based storage oscilloscope
So you are digging into the inner workings of the detector itself?
One interesting thought is that if there is a constant rail-rail current (think resistor wheelset) detectable current should flow during the entire DCC waveform cycle (except during the 1-2 uSec or so during voltage reversals).
Most detectors are sensitive to peak currents during the switching interval as well as during the rest of the steady value portion of the ½ DCC waveform. These can be fooled by peak currents that flow due to capacitive effects of wiring and/or track as this often causes polarity charging and sometimes oscillating currents to flow. NCE type boosters with fast voltage transitions aggravate this issue.
For CT type detectors with a doughnut hole there is an interesting way to connect a capacitor backwards to counteract the effects of wiring capacitance. Look for it within the bowels of wiringforDCC notes and photos.
An interesting twist would be for a smarter uP inside the multi-channel detector to look at the condition of current signals only after the voltage transients of DCC track voltage switching are likely to have passed. If the detector circuitry is powered by DCC that possibility is relatively easy. Sync the current detection interrogations of individual channels to be synchronous with but slightly delayed from DCC voltage transitions.
I’m not sure how Dick B of RR CirKits does it, but it is worth mentioning.