PTZ intermitant control problem

[icuthere 0]

Hi There,

got a problem with a PTZ system comprising of joystick controller,DVR and four PTZ domes (pelco d). System works fine but quite often when panning a ptz then releasing the joystick the camera keeps panning and the only way to stop it is by selecting another camera. The problem occurs intermittantly and usualy when panning at slow speed. The system cabling is "star" configuration with the termination resistors in the PTZ furthest from the controls. Any suggestions would be gratefully appreciated please.

[shockwave199 0]

Maybe it's the joystick controller. Have you tried cleaning it? Maybe an appropriate electronics spray cleaner would help.

[icuthere 0]

Thanks but tried a different controller even, same problem. Was thinking maybe something wrong with the control wiring or termination resistors. Wnder if anyone else heard of this problem?

[tomcctv 190]

hi remove resistor from camera. not needed in star.

 

also do you only have 1 pair to each camera. and are you using 2400 or 9600

[icuthere 0]

I assumed you needed resistors wether star or daisy chain? using 9600 baud, a pair for each camera

[ilk 0]

I assumed you needed resistors wether star or daisy chain? using 9600 baud, a pair for each camera

 

RS485 is not designed for star wiring.

 

You need to either install a RS485 distributor or rewire in series with end of line terminated.

 

Ilkie

[survtech 0]

I assumed you needed resistors wether star or daisy chain? using 9600 baud, a pair for each camera

I agree with ilk. RS422/485 is not designed for star distribution. It is possible to use a code distribution unit, like Pelco's CDU-T or GE Security's Kalatel KTD-83 at the hub but if you just tie multiple control lines to one port, you are likely to run into control problems.

 

Daisy-chaining multiple PTZs is always an option. Common practice is to only terminate the device at the end of the chain while leaving devices in the middle of the chain unterminated but I've found that you can terminate up to at least three devices in a daisy chain with no effect on operation. Although the resulting termination would be 33 ohms (100/3), RS422 drivers have no problem handling the increased load.

 

The problem with only terminating the end of the chain is that if the end device is removed, there would be no termination; which can cause control signals to reflect up and down the line and interfere with proper operation.