Watlow CAS200 - Manual (Page 42)

Chapter 2: Installation CAS200 User’s Guide
30 Watlow Anafaze
Avoiding Noise Problems
To avoid noise problems be sure ground wire terminal (on
TB2) is connected to earth ground.
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
CAS200 series equipment.
Separate the 120/240Vac power leads from the low level
input and output leads connected to the CAS200 series
scanner. Don't run the digital output or control output
leads in bundles with 120/240Vac wires. (Never run input
leads in bundles with high power leads).
If you must use EM relays and you must place them in a
panel with CAS200 series equipment, use a 0.01
microfarad capacitor rated at 1000Vac (or higher) in series
with a 47
Ω, ∫ watt resistor across the NO contacts of the
relay load. This network is known as an arc suppressor or
snubber network.
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 130Vac for 120Vac control
circuits across the load, which limits the peak AC voltage
to about 180Vac (Watlow Anafaze P/N 26-130210-00). You
can also place a transorb (back to back zener diodes) across
the digital output, which limits the digital output voltage.
The above steps will eliminate most noise problems. If you
have further problems or questions, please contact Watlow
Anafaze.
Digital Outputs
The CAS200 scanner provides 35 digital outputs. The
digital outputs sink current from a load connected to the
scanner's internal power supply or from an external power
supply referenced to the scanner analog common.
• If you use an external power supply, do not exceed +24
volts.
• If you tie the external load to ground, or if you cannot
connect it as shown on the following page, then use a
solid state relay.
• If you connect an external supply to earth or
equipment ground, use solid state relays to avoid
ground loop currents. (Ground loop currents may
degrade analog measurements in the scanner.)
The outputs conduct current when they are LOW or ON.
The maximum current sink capability is 60mA at 24Vdc.
They cannot “source” current to a load
.