Watlow Controls 8LS, Руководство пользователя

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16 8LS User’s Guide
Installation
Noise Suppression
When using the digital outputs from Watlow Anafaze multiloop
controllers to energize dry contact electrical-mechanical relays with
inductive loads, generation of RFI may become a problem.
This may cause the 8LS display to blank out and then re-energize as if
power had been momentarily turned off. It may also cause the CPU in
the equipment to reset, losing the PID output levels. It may also damage
the digital output IC circuit, thus not being able to energize the digital
outputs. If the IC circuit is damaged, factory repair will be required.
The type of loads that may cause a problem are motor starters, alarm
horns, etc. The RFI is generated upon opening of the metallic relay
contacts.
To correct the problem of RFI noise problems:
1. Use Solid State Relays (SSR) wherever possible in place of electrical-
mechanical relays (E-M relays).
2. When using E-M relays, if possible do not mount them in the same
panel as the Watlow Anafaze equipment.
3. Separate the 120 vac power leads from the low level input and out-
puts leads from the Watlow Anafaze. Do not run the digital outputs or
PID control outputs leads in the same wire bundle as any 120 vac
wires. Inputs leads should never be run in the same bundle with any
high power leads.
4. If E-M relays are required and must be in the same panel as the Wat-
low Anafaze equipment, use a .01 uF at 1000 vdc or higher vdc disk
capacitor in series with a 47 ohm 1/2 W resistor across the NO con-
tacts of the relay load contacts. This is the most important step in sup-
pressing RFI from relay contacts. This network is known as arc
suppressor or snubber networks.
5. Use of other voltage suppressing devices may also be used, but are
not normally required. A device known as a MOV rated at 130 vac
for 120 vac control circuits may be placed across the load. This will
limit the peak ac voltage to about 180 vac. A device known as a tran-
sorb (back to back zeners) may be used across the digital output. The
rating of 5 vdc should be used. This will limit the dc voltage to 5 vdc
on the digital output loop.
See diagrams for proper placement of the above devices. The parts for
RFI suppression are available from Watlow Anafaze.