sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services Security, Alarms and Paging PTZ Cameras

Installing 3 P/T/Z Dome cameras for a client Thursday.

Am I to understand correctly, that the RS485 wires can be Daisy Chained to each camera?

(Example: from DVR to camera-1 then to camera-2 then to camera-3.)

The cameras do have Dip switches to set their individual address.

Kirk

Well yes, technically they can be daisy chained. It is a better practice to home run each camera back though.

Depending on the brand, some use 2 conductors and some use 4 conductors for the RS485 protocol. If you use cat5, you will have spares. You can use one spare pair with a video balun and not have to run additional coax with the cat5.

I had an install that only needed 2 conductors (1 pair) for the 485, I used one pair for the video, and I doubled up the last 2 pairs and sent the power up it. The distance to the cameras was minimal so I could get away with this.

We always homerun each camera no matter what it says, no matter what kind of camera. We have actually run spares as well to some, more critical-use cameras. Cable is not that expensive, even for the customer who frequents the blue light specials. Good luck!

I don't know anything about this equipment. But I know RS-485 is a balanced 2-wire serial communication protocol. It is the same protocol used in DMX theatrical equipment to send dimmer/color values and lens/mirror postions (basically pan/tilt/zoom).

In theater, the cable MUST be daisy chained, or else use an expensive repeater hub (aka "active splitter").

In most uses, the RS-485 signal is one way - from the controller out to the instruments. This uses a single pair of wires. The DMX standard cable is supposed to be 2 pairs. Some manufacturers have put return communication on the second pair, from the instruments back to their proprietary controllers. Breaks the standard.. but that's another story.

Well here goes my soapbox:

Yes, you are right Rob, DMX is the same thing - RS485. This is a communication that uses one pair (2 conductors) and it is normally daisy chained "out" to "in" with an end of line resistor (terminator) on the last fixture.

With lighting, they normally have two connectors on each fixture labelled "in" and "out." You address your fixtures and the last fixture has to have the EOL turned on either with a dip switch, or some are automatic. If you don't plug anything into the "out" jack, it will terminate with the required 120ohm resistor. By the way, although they don't recommend it, you can split a DMX cord (wye adapter) and it probably will work (without the active hub). I have seen it done before. Obviously you lose the EOL, but there is enough signal to over come the "reflection" in the non terminated cable to make the fixtures work. This is just like wying a video signal. It will work, but eventually the signal degrades enough (due to reflection) to make a visual difference. That's why you should always use the in/out loops on CCTV monitors and enable the 75 ohm terminator on the last monitor (that's another soapbox).

PTZ controllers and DVR's all do it differently according to brand.

Some have individual in/out for each PTZ camera. They might be labelled Tx+,Tx-,Rx+,Rx-. I have also seen Tx+,Tx-,Tx1+,Tx2- and OUT +,-, IN +,-. Some units only supply one RS485 hook-up for the entire loop and in this case you would have to join the return pair from camera 1 to the send pair on camera 2 using beenies when home running. Obviously any of these methods uses 2 pairs on the cat5. The last camera may use one pair with the terminator turned on or some controllers/DVR's have a return/receive terminal that basically has a resistor across it.

Some manufacturers only use 1 pair period. It could be they are using RS232 instead (there are some out there). And I know one company that uses 1 pair, RS485, and they tell you to parallel the connection to all cameras either right at the controller or on each camera. I'm not sure how they are doing this, maybe like the DMX "wye" that I explained earlier. The funny part is they tell you in the instructions to turn on a EOL dip switch in your last camera. How would you determine your last camera and shouldn't each line be terminated? It does seem to work though.

So as you can see, because of the different standards and protocols the manufacturers are using, I still think home running is best. This will give you the best options for future installs and you will be able to mix and match different brands of PTZ's by using RS232 to 485 converters.

BTW, "up the coax" PTZ control is sweet. No data line has to be run at all, just your video.

If there's an in/out for each, then is it likely the controller has the repeater internally?

I know about the DMX wye. Basically instead of terminating each run with the standard 120 ohms, you need two, whose parallel totals 120... which works out to 240 ohms each.

I'm guessing yes.

The strange part is on the fixtures, (whether it be an intelligent light fixture or a PTZ camera) the in/out are just wired in parallel. So the tap off for that particular unit is just like a wye. I guess the reason it works, is the tap is very short so no reflection problems?!!

Yeah... I keep hearing the term "snub network" on a DMX bulletin board.

OFF TOPIC
Electrically, Cat5 cable is a perfect cable for DMX. The only difference is there are 2 extra pairs and it's not shielded. Most cheap DMX installs use microphone cable between the units, which does not have the same twist rate required by the specs.

I have one long run from the rear to the sidewall with my first light boom. That run is cat5, with XLR's soldered on. The other 3 runs are microphone cable, but I'm intending to replace them as well. I've been looking for cheap cat5 shielded patchcords (flexible/stranded) to convert into DMX patches. In the meantime, I have to terminate the controller end in a box, because the XLR gets a lot of abuse being plugged and unplugged for each show and rehearsal. I'm trying to decide if I should punch down an RJ45, or get a chassis-style XLR socket.

Sorry to hijack the thread.....

I have confirmed this issue with the maufacture of the particular cameras we are installing.

The RS485 signal is very common and usefull in this type of enviroment. Be it PTZ cameras, Lighting controls, or many other automated services.

It's a 2 wire (1 pair) configuration with a Positive + and a Negative -. To connect equipment to the system, you basically Wye, or split of each wire to the equipment.

The last piece of equipment either has a switch or a connection for a termintor. Cat-5 is perfered even by the maufacture.

Thank you for you help on this matter.

Please see my new post (GeoVision Yea or Nea) as I have another situation.