Red Lion PCU - Manual (Page 60)

SERIAL CONNECTIONS
When wiring the terminal block at the rear of the unit, refer to the label with
the terminal description for installing each wire in its proper location. It is
r e c o m m e n d e d t h a t s h i e l d e d ( s c r e e n e d ) c a b l e b e u s e d f o r s e r i a l
communications. This unit meets the EMC specifications using Alpha #2404
cable or equivalent. There are higher grades of shielded cable, such as four
conductor twisted pair, that offer an even higher degree of noise immunity.
Only two transceiver wires and a common are needed.
The two data (transceiver) wires connect to the TX/RX(+) and TX/RX(-)
terminals, appropriately.
The cable should consist of a shielded twisted pair and in some applications
a signal ground may be required to establish a ground reference. The signal
ground is required if the equipment does not have internal bias resistors
connected to the RS485 transceiver lines. The signal ground is connected at
the RS485 common of only one PCU unit to the RS485 equipment. If
necessary, the shield can be used as the signal ground.
The signal input common is isolated from the RS485 common and the
analog output “-” terminal.
Note: Do not connect any of the commons to the analog output “-” terminal.
Terminal Descriptions
RS485 COMM. - Common may be required for communication hook-up.
TX/RX(+) & TX/RX(-) - The PCU transmits and receives on these two
terminals which are connected to the external device.
TX EN. - Used with a Red Lion Controls (RLC) GCM422 Serial Converter
Module (RS422 to 20 mA Loop). Otherwise not normally used.
Note: Some models do not have TX EN. This is an output used in conjunction with
interface converter Model GCM422, to convert RS485 to 20 mA current loop.
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