Watlow CLS200 Manual de usuario descargar pdf (Pagina 39)

CLS200 Series User’s Guide Chapter 2: Installation

Doc.# 0600-3050-2000 Watlow Anafaze 23

Avoiding RFI/EMI

• To avoid or eliminate most RFI/EMI noise problems:

• Connect the CLS200 case to earth ground. The

CLS200 system includes noise suppression circuitry.

This circuitry requires proper grounding.

• Separate the 120 or 240V

Å (ac) power leads from the

low-level input and output leads connected to the

CLS200 series controller. Do not run the digital I/O or

control output leads in bundles with ac wires.

• Where possible, use solid-state relays (SSRs) instead

of electromechanical relays. If you must use electro-

mechanical relays, try to avoid mounting them in the

same panel as the CLS200 series equipment.

• If you must use electromechanical relays and you

must place them in a panel with CLS200 series equip-

ment, use a 0.01 microfarad capacitor rated at

1000VÅ (ac) (or higher) in series with a 47 Ω, 0.5 watt

resistor across the N.O. contacts of the relay load. This

is known as a snubber network and can reduce the

amount of electrical noise.

• You can use other voltage suppression devices, but

they are not usually required. For instance, you can

place a metal oxide varistor (MOV) rated at 130VÅ for

120VÅ (ac) control circuits across the load, which lim-

its the peak ac voltage to about 180VÅ (ac) (Watlow

Anafaze part number 26-130210-00). You can also

place a transorb (back-to-back zener diodes) across the

digital output, which limits the digital output voltage.

Additional Recommendations for a Noise Immune System

It is strongly recommended that you:

• Isolate outputs through solid-state relays, where pos-

sible.

• Isolate RTDs or “bridge” type inputs from ground.

• Isolate digital inputs from ground through solid state

relays. If this is not possible, then make sure the digi-

tal input is the only connection to earth ground other

than the chassis ground.

• If you are using EIA/TIA-232 from a non-isolated host,

either (1) do not connect any other power common

point to earth ground, or (2) use an optical isolator in

the communications line.

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