2.33
Two outputs are available - 20mA current loop and RS 232C.
1. Current Loop:
To maintain EMC requirements, connection to TB-G must be made using a screened
cable having two twisted pairs. The screen termination is made only at one end
(generally at the 1102 Interface Unit in maximum separation configuration) and the
terminating wire must be maintained as short as practical (less than 40mm).
Connection is made to the lower (TB-G) of the two connector blocks on the front of the
board.
Terminal 1 (top) - No connection
2 - No connection
3 - Tx -ve
4 - Common (No connection)
5 - Tx +ve
2. RS 232C:
The current loop output should be used whenever possible and the RS 232C only for
connection to local digital equipment.
If the 20mA current loop is not in use, then on the lower connector block (TB-G) link the
following terminals:
Terminal 1 to Terminal 3
Terminal 2 to Terminal 4
Connection is made to the upper terminal block (TB-K) on the front of the board.
Terminal 1 (top) - No connection
2 - No connection
3 - Data output
4 - No connection
5 - Common
The cable must be a screened, twisted pair, not exceeding 3 metres in length and having the
screen terminated within the 1101 Control Unit enclosure. Screen terminations must be kept as
short as practical (less than 40mm). The recommended conductor size is 16/0.2mm (20 AWG),
or greater, since a smaller conductor may not be adequately clamped by the screw terminals.
This cable must not be installed close to other cables or equipment likely to generate severe
levels of electromagnetic interference.
In systems using an Interface unit, the RS232C output is only available from the Control unit.
The output of the digital data communications board is not intrinsically safe. In hazardous
applications connecting cables should conform to the relevant certification requirements. For
details of protocol and interpretation of data stream see Appendix 4.
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