Watlow PPC-2000 - Manual (Page 60)

Chapter 2: Hardware Installation PPC-2000 User’s Guide
36 Watlow Anafaze Doc.# 30002-00 Rev 2.3
electromechanical relays, alarm horns and motor starters.
Such devices may generate electromagnetic interference (EMI
or noise). If the controller is placed close to sources of EMI, it
may not function correctly. Below are some tips on how to
recognize and avoid problems with EMI.
Symptoms of RFI/EMI
If your controller displays the following symptoms, suspect
EMI:
• Measured values for analog inputs fluctuate or are
incorrect.
• Open collector outputs fail.
• The watchdog time out LED on the Processor Module
lights.
EMI may also damage the digital output circuit—so digital
outputs will not turn on. If the digital output circuit is
damaged, return the controller to Watlow Anafaze for repair.
Avoiding Noise Problems
To avoid RFI/EMI noise problems:
• PPC-2022 32 analog input module must be used with
isolated (ungrounded) thermocouples only.
• PPC-2022 32 analog input module should not be used with
thermocouples that are embedded within heaters as some
cartridge heaters are constructed.
• Separate the 120 or 240Vac power leads from the low level
input and output leads connected to the controller. Don't
run the digital I/O or control output leads in bundles with
120Vac wires.
• Where possible, use solid state relays (SSRs) instead of
electromechanical (EM) relays. If you must use EM relays,
try to avoid mounting them in the same panel as the PPC-
2000 series equipment.
• When switching an inductive load such as an
electromechanical relay or solenoid, install a snubber
across the load. Use a 0.01 microfarad capacitor rated at
1000Vac (or higher) in series with a 47 Ohm, 0.5 watt
resistor across the NO contacts of the relay load. See
Chapter 2, Connecting to the Relay Outputs on the PPC-
206x on page 70 for specific instructions on using snubbers
with the PPC-206x modules.