I want to thank everybody who wrote suggestions and discussion. I'll
try to answer all the questions and share my proposed line of attack
for your comments. Whatever I do, I really would like to find some
test that I can apply by myself. Having to wait for the next
operating session at my house doesn't appeal. Nor does trying to
debug the detectors while the guys are trying to run trains.
My layout is in a 20' x 24' room. I have a dehumidifier, but haven't
turned it on yet for the season. In the winter I use a humidifier,
but in spring and fall I don't need either.
The block being detected is 14' of straight track followed by a rising
curve about 15' long that p***** over the straight track. Both ends
are gaped. Power from the booster is distributed using 12 gauge wire
power bus running roughly parallel to the track. When I decided where
the detection block was, I disconnected all the feeders on one rail
from the bus and connected them to a sub-bus that is about 18' long.
The detector circuit board is near one end of the sub-bus. The wire
from the detector to the bus is about 1' long.
I measured resistance between the rails using an auto-ranging ohm
meter; it measured as an open circuit. I realize that's a DC
measurement, but I don't have any way of measuring at DCC frequencies.
It seems that some people refer to one pass of the track lead through
the coil as one-half turn while others call that one turn; I'll use
the latter. If there's a difference in configuration between one-half
turn and one turn it escapes me.
I am planning to have 5 detection blocks. So far I have two
configured. Only one of the detectors is showing the false detection.
That presents several ideas. (1) I could switch the detectors and see
what happens. (2) I could replace the detector that is giving the
false positive with one that I haven't used yet. (3) I could try
putting both detectors on the same block in series.
I adjusted the sensitivity to detect the caboose by experimenting with
number of turns through the inductor coil and the resistance across
the track. With one turn it could detect 2K ohm. With two turns it
detected 5K. I decided that was sensitive enough and wired 9.6K
resistors between the wheels of two axils on the cabooses. In
general, I'm still using plastic wheels, so I purchased new metal
wheel sets. I confirmed detection of cabooses.
I tried the dry finger test. The false positive detector switched
states and the other did not, confirming that the first detector is
more sensitive.
That's all I can think of now. I'd appreciate comments on my ideas of
things to try or other ideas.
|
