AMETEK 1995L Micro-Set PLS - Manual (Page 23)

19 Installation and Maintenance Manual
Chapter 7: Troubleshooting
If the LDT cable must be run through a terminal strip, it must be mounted in a small enclosure with no
other wiring. The shields of the incoming and outgoing cable must be tied together and isolated from
ground.
Special purpose contact inputs all operate by connecting the input pin on the 1995L PLS to a power or
GND terminal (depending on method wired per Fig. 10-1, Fig. 10-2, Fig. 10-3 (Chapter 10: Wiring
Diagrams) on the 1995 PLS through a remote contact or solid-state switch. These computer level
signals must be protected from induced electrical noise.
The contact used to activate the input should not be located outside the enclosure in which the 1995
PLS is mounted. Any wiring between the 1995 PLS input terminals and this contact located within the
enclosure should be routed away from any power handling relays, contactors, or other noise generating
devices.
If the input is to be activated by a remote device, the contact of the remote device should be used to
energize a relay within the enclosure. The contacts of this relay are wired to the 1995 PLS input
terminals.
7.4: Incoming Power
Solenoids, welders, large motors, and variable-speed drives are all devices that generate excessive
electrical noise throughout the power grid in a typical industrial environment. Isolation transformers or
constant voltage type power supplies should be used to isolate microprocessor-based circuitry. The
power on the output side of these isolation devices should be fed to the programmable limit switch and
other microprocessor-based devices only. The loads being driven by the programmable limit switch
output relays must not get their power from the output side of the isolation device. Using the output
side of an isolation device to power loads other than the programmable limit switch totally defeats the
purpose of the isolation device.
NOTE: When using an output relay for driving inductive loads such as solenoids, a noise suppression
device must be installed across the coil of the load. Use an MOV or RC noise suppressor
for AC loads, or a commutating diode for DC loads.
7.5: Low Level Inputs
Low level inputs to the 1995L PLS include the LDT cable and other special purpose contact inputs
such as reset-to-preset, fault check, and security.
The LDT should be wired to the 1995 PLS using an uninterrupted run of cable with a shield. Whenever
possible, this cable should be run in a conduit by itself. If it must run in a conduit with other wiring, this
wiring should not include power wires above 110V AC or wires driving noise producing loads.