Block Detectors 101

[Sumpter250]

And to try to get a handle on what the description...."The logic output of the detector is open collector means, which I assume is the basis of all understanding.

While I've never heard the term " Open Collector ", used in logic circuits......digital, as I learned it, assigns "high" (open circuit voltage) to "1", and "low" ( short to ground ) to "0".
If the collector of a transistor is "open" it's " output " is the applied operating voltage ( typically 5 Volts DC ), and is a "1" or high.

The other thing I learned about logic circuits is that a "1" or "high", is a "true statement".
So......
If the output of the detector is "Open Collector / high /"1"/"true", then there is something in the block.
If the output of the detector is "closed ? collector" / low / "0" /false, then the block is empty.

Only something in the block that draws current. ( loco, lighted car, or cars with resistive axles "resistor wheel sets" ) will cause the detector to output " Open Collector" / etc.. Rolling stock that does not have some form of current drawing capability, is, "invisible" to the detector.
Hope that helps.