User`s manual

Watlow Controls Communications Guide 22
Summary
As first stated in this article, the steps involved
to communicate are:
1. Determine how many controllers you
will communicate with
2. Pick a protocol and interface that
supports the information exchange
3. Purchase hardware and software to make
this happen.
The number of controlled zones will determine
the number of controllers connected to the PC or
PLC. Pick a protocol that will support this
number. Consider speed and reliability of
communications when picking the protocol. Ask
yourself, how will the devices understand each
other? Pick an interface that will support the
number of devices connected, transmit over the
desired distance and is industrially hardened
(will communicate in electrically noisy
environments). Lastly, purchase an interface,
controllers, PC or PLC and software that will
work together. Software may be written to
accomplish the task if you have the skills and
resources to do so.
Interface Comparison
Interface Maximum Max # Cable Voltage Balanced/ Duplex
Standard Bus Length Controllers Type Level Unbalanced
EIA-232 50 feet 1 3-wire 3 – 24 v Unbalanced Full
EIA-423 4,000 feet 1 3-wire 3 – 12 v Unbalanced Full
EIA-422 4,000 feet 10 5-wire 2.0 – 6 v Balanced Full
EIA-485 4,000 feet 32 3-wire 1.6 – 6 v Balanced Hal