Rs-422, RS-485 PTZ Camera Compatibility

[Mattb 0]

Has anyone used PTZ cameras listed as RS-485 on an RS-422 controller? I want to add additional PTZ cameras to a Pelco 97xx system that is native RS-422, Pelco-P protocol @ 4800 baud.

 

I don’t want to use a protocol converter – I am looking for manufacturers cameras other than Pelco to add to the system.

 

I am looking specifically at the GE/UTC TruVision Mini PTZ, which has a "RS-485 communication DIP switch" supporting a "Digiplex RS-422 mode." There is also a “Pelco-P” mode.

 

The manual clearly states “RS-485 is the interface that connects the dome camera to the control device. Consequently the RS-485 setup of the dome camera and the control device must be

identical.”

 

A call to the manufacturer’s support group gave a positive answer, but I have some concerns after reviewing the manual. My Vendor can not say for sure either.

 

Internet searches of RS-485 and RS-422 compatibility haven’t specifically addressed camera compatibility, but have provided enough information that I am not eager to experiment.

 

So, can anyone share experiences using PTZ cameras listed as RS-485 on Pelco RS-422 systems without a converter? Pelco systems would be the 6700, 6800, 97xx matrix systems,or even a KBD300A. Thanks.

[survtech 0]

The primary difference between RS422 and RS485 is that RS422 is unidirectional and RS485 is bidirectional; which means one-way vs. two-way. Since PTZs only require one-way communication (except maybe for alarms), the two communication standards are basically the same.

 

Assuming you are sending one-way data only (not two-way), you can use devices like the Kalatel KTD-83 or the Pelco CDU-T for either system.

 

http://www.rs485.com/pfaq.html

[Mattb 0]

Great information survtech,

 

I see there are some physical differences in the standards, like input and output voltage, termination etc.

 

Have you ever put an RS-485 PTZ camera on a RS-422 controller?

[survtech 0]

I think I did that in one casino without problems. It was 7 years ago so my memory is foggy but it seems to me that I determined it doesn't matter. The key is that the protocols match and you make certain that TX+/- on the controller connect to RX+/- on the PTZ (+ to + and - to -). As far as I know, all PTZ controls are terminated with 100 to 120 ohms.

 

In fact, you can daisy-chain a fairly large number of PTZs on a single control wire. In fact, despite recommendations to the contrary, we daisy-chain up to 3 PTZs on a single control cable and leave the terminations "on" for all 3. Although that makes the net termination resistance approximately 33 ohms, we've never had a problem.

 

In fact, I once talked to the owner/engineer at Sennetech (they make code translators) and he told me that a casino in Las Vegas had around 100 terminated PTZs daisy-chained on one control port and the system still worked. That's a net impedance of 1 ohm.

[Mattb 0]

Thanks Carl,

 

That’s exactly what I wanted to hear. Pelco makes some nice product, but it is time to explore some less expensive PTZ cameras.

[prosinger 0]

Thanks Carl,

 

That’s exactly what I wanted to hear. Pelco makes some nice product, but it is time to explore some less expensive PTZ cameras.

 

I think I have the oposit to you. I'm running two PT&Z from a RS485 controller and now want to add an American Dynamics PT&Z which runs from a RS422. I've tried most combinations of wiring up but can't get the RS485 controller to operate the new camera. Any suggestions as tou your solution might help.

Brian