speed dome chassis, as shown in figure three. When the speed dome leave the factory, 120
Ω
matched resistance
is not connected as default; users can set the 8
th
bit of the sw2 on to connect the matched resistance, on the
contrary, if users don’t want to connect the matched resistance, turn the 8
th
bit of the sw2off.
Figure 3
4. The problems in practical
Users are likely to use star connection in practice, at this time match resistance should be connected at the two
devices that most apart (In figure four, those are device one and device 15). But as this connection way does not
meet the RS485 Industry Standards, problems like signal reflex, decreasing of resisting disturbance capacity are
likely to take place when the device are long away from each other, and result in the reliability of control signals
coming down. In this case, speed dome may be completely uncontrollable, or scan with no way to stop it.
Figure 4
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