PMDX Forum
General Category => SmartBOB controllers and dedicated accessories => Topic started by: dq828 on April 25, 2017, 03:20:33 AM
-
Iv? read that Limit switches should be run Active High, at the moment I'm running them Low. I have my Limit switches on inputs 1 - 6, do I just move the Ground wires to the +12V inputs to achieve this?
-
Is there anybody out there :)
-
Perhaps you are confusing "active high" with "normally closed".
These are related, but not the same concept.
It is desirable to use a normally closed circuit to sense home or limit
switches because a failure of connectors or wiring will result in the
system stopping in a safe fashion. Normally open sensors will also
work, but the wiring failure fail safe advantage is lost.
The inputs of the PMDX-424 interface board is internally pulled to +5
volts by a resistor. If you connect a normally closed switch between
the input signal and ground, the signal is normally low. Therefore
you would configure Mach for "active high" operation. The is the
default setup with a red X in the box labeled active low, indicating
that active low operation is not being requested. Yea, I know, it
is confusing.
If you have proximity sensors things can be more complicated. These
sensors can be normally open (most common) or normally closed,
and they can be NPN (ok for the PMDX-424) or PNP (requires use of a
PMDX-105 for level conversion).
-
Thank you, I agree it is confusing!
The bottom line as far as I see it is I have to rewire all the limit switches so they are NC!!! And then change the Limit Switch setting to Active High.
Thanks again
-
I would agree that rewiring is the best solution in your case.