Watlow CAS200 - Manual (Page 41)

CAS200 User’s Guide Chapter 2: Installation
Watlow Anafaze 29
EIA/TIA-485 Converters and Laptop Computers
For a 232-to-485 converter to optically isolate the computer
from the 485 network, the 232 and 485 sides must be
powered independently. Many 232-to-485 converters can
be powered by the computer’s communications port. Some
computers, laptops in particular, do not automatically
provide the appropriate voltages. These computer/
converter combinations can usually be used by connecting
an external power supply to the 232 side of the converter.
Not all converters have power inputs for the 232 side,
however.
Wiring Digital I/O
This section describes how to wire and configure the alarm
outputs for the CAS200 series scanner.
All digital outputs are sink outputs referenced to the
CAS200 common. These outputs are Low (pulled to
common) when they are On.
All digital inputs are Transistor-Transistor Logic (TTL)
level inputs referenced to control common.
The digital I/O are located on the (EIA/TIA-232 remote
TB50.
Noise Suppression
The CAS200 outputs are typically used to drive solid state
relays. These relays may in turn operate more inductive
loads such as electromechanical relays and alarm horns.
These devices may generate electromagnetic interference
(EMI or noise). If the scanner is placed near 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 scanner displays the following symptoms, suspect
EMI.
• The scanner's display blanks out and then reenergizes
as if power had been turned Off for a moment.
• The process variable does not display correctly.
EMI may also damage the digital output circuit—so digital
outputs will not energize. If the digital output circuit is
damaged, return the scanner to Watlow Anafaze for repair.