Watlow Electric Revision 5 - Manual (Page 25)

20
Distance Wire Gauge Recommended Cable
1500 ft. 28 AWG Alpha 3492
4000 ft. 24 AWG Beldon 9729
6000 ft. 22 AWG Beldon 9184
The use of a shield depends on the noise environment and grounding
considerations [4.3.3]. The above cables are shielded.
4.3.3 Connections
Connection of the Anafaze controllers to a system computer requires an
interface at the computer to convert RS-232 levels to RS-485. Anafaze
recommends Black Box Model LD485A for this purpose. The LD485A
should be configured for DCE operation, with the RTS/CTS delay jumper in
the "on" position.
The RS-485 specification is for "balanced line" operation, and is not true
differential. Thus a common connection is required between all stations on
the communication line. This can be accomplished by either a 5th wire
(which could be shield) or a common ground connection. The Anafaze
system more conveniently supports the common ground connection,
although 5th wire can be supported if required due to common mode
voltages generated in a given installation. The 5th wire connection would be
required only if the "common mode" voltage between stations exceeds the
RS-485 specification of 7 volts peak. The power common in the Anafaze
controller has been wired to chassis ground. To make sure the
communication system works, the controller chassis must be electrically
tied to Earth ground, and the host computer communication must be tied to
Earth ground. If the host computer RS-232 communication is not referenced
to Earth ground, then install the 100 ohm resistor in W7 as recommended by
Black Box.
Figure 1 shows the only recommended system hookup. (Other hookups may
work fine). The transmitter from the host computer connects in parallel to
the controller receivers, and the host computer receiver hooks in parallel to
the controller transmitters. A single "daisy chain" is recommended. Octopus
connections or "spurs" are discouraged. A termination resistor is required at
each end of the transmission line. This is accomplished by applying a 200
ohm resistor across the line at the farthest point from the computer
transmitter, and by setting the Black Box SW2 to the "term" position to
terminate the computer receive line.