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TB035 Rev1 Isolating Limit Switch Failures on an M15
Overview
This document describes the procedure to be used to isolate limit switch failures on an M15 It is assumed that
there is a known failure of the limit switches or wiring up to the point where the limits enter the back panel of
the control It applies to the M15 5 and M15 6 models
The connection points
There are several points of connection for the limits The first point of connection is at the limit switch itself
The second point of connection is inside the transformer box and the third is at the back panel of the control
Internally there is a connection from the back panel of the control to the motor drive itself
Where to start
The first step to take is to ensure that the connection points are tight This means that the limit switch cable at
the back of the control panel is checked as are the connections on the terminal strip located in the
transformer box at the bottom Having checked these connections run a simple program and see if you can
provoke the error by tapping lightly on the limit switches and by moving or shaking the limit switch wiring if
possible This technique may give clues as to where the problem lies
Eliminating the switches
To eliminate the limit switch itself as a problem take the wires that go to it and tie them firmly together In
some cases this may require that the limit switch housing be disassembled If errors occur the problem lies in
the wiring If no errors occur the switch is faulty Note that while the wires are shorted the motor drive will not
stop movement if the switch is triggered Therefore use caution when moving the table about or running a
program without travel limits in effect Do not measure the resistance of the switch contacts when they
are opened and closed to determine if the switch works
The only time measuring resistance is valid for
control troubleshooting purposes is when the resistance indicates that the switch is completely failing to
electrically open when the switch is tripped or that the switch is not closing when released
Isolating the problem at the transformer box
This is often the best place to start if there are no clues as to what may be causing the problem To perform
this test jump the offending switch or switches inside the transformer box at the terminal switch for a model
M15 5 control or prior See the label inside the transformer box For an M15 6 the limits are wired into the
back panel of the control In both cases have a certified electrician examine the control wiring schematics If
the problem goes away it must have been in the limit switches or the wires coming to the point just jumped
Document History
Rev1 Created on 1998 04 15