19
form (refer to Picture 2).
1) In the Picture it is the factory default connection. The jumper is seated on Pin2&Pin3 and
the termination resistor is not connected.
2) when connecting the 120
termination resistor, user should plug the jumper on
Pin1&Pin2. and the termination resistor is connected.
4. Problems in practical connection
In some circumstances user adopts a star configuration in practical connection. The
termination resistors must be connected to the two equipment that are farthest away from each
other, such as equipment 1# and 15# in Picture 44. As the star configuration is not in conformity
with the requirements of RS485 standards, problems such as signal reflections, lower
anti-interference performance arise when the cables are long in the connection. The reliability of
control signals is decreased with the phenomena that the dome does not respond to or just
responds at intervals to the controller, or does continuous operation without stop (refer to Picture
39).
Figure 39
In such circumstances the factory recommends the usage of DR-HB16 RS485 distributor.
The distributor can change the star configuration connection to the mode of connection
stipulated in the RS485 standards. The new connection achieves reliable data
transmission (refer to Picture 40).
Appendix :
Figure 40
Wire Diameter and Transmission Distance Comparison Chart
