Section 5
Page 5 - 28
HA243821
Issue 5 Mar 98
MODEL 346 INSTALLATION AND OPERATION MANUAL
5.7.2 INSTALLATION (Cont.)
TERMINATING RESISTOR
At the recorder furthest from the host computer, it is recommended that a 220
Ω
resistor be fitted across the
recorder Rx+ and Rx- terminals to reduce unwanted signal reflections. The resistor can be of almost any type,
but 1/4 Watt is recommended for mechanical strength coupled with manageable size.
BIASSING RESISTORS
At one of the recorders in the link, the recorder Tx- terminal must be ‘pulled down’ to signal ground and the Tx+
terminal must be ‘pulled up’ to 5 Volts, using 470
Ω
resistors. As the Terminating Resistor has to be fitted at the
end of the link, it is recommended that the biassing resistors are also fitted there as shown in figure 5.7.2 above.
For resistor type, see under ‘Terminating Resistor’ above.
Figure 5.7.2b Communications link connector locations
CAUTION
DAMAGE WILL BE CAUSED TO THE TERMINAL BLOCKS IF THE SCREWS ARE OVER-TIGHTENED. THE
RECOMMENDED MAXIMUM TORQUE IS 0.4 Nm.
L
N
-
+
-
+
-
+
The communications terminals are shown here in option board 3 position (Slot 5).
The board can alternatively be fitted in option board position 1 (slot 3) or 2 (slot 4)
provided the position is free. See section 2.4.5 for further details.
Rx-
Tx-
5V
Rx+
Tx+
0V
-
+
-
+
-
+