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There are several types of data that can be used for control. We use RS485 data as this is the most robust type of data. It is a, multi-drop, balanced pair system and can send data up to 1km on a twisted pair cable. Our data rate is 9600baud.
Some other types of data are:
RS422 - Similar to RS485 but only point to point.
On our system, up to 10 cameras and heads can be connected in a ‘daisy chain’ manner to a controller. Alternatively up to 99 heads can be controlled using a distribution amplifier or via a radio data link provided this allows ‘streaming’ of the data. The remote heads manage all the data and error handling internally and are optimised for live action control. Each head recognises its own ident, therefore the same radio frequency and data stream can be used for all heads.
Slip Rings, when fitted, enable electrical connections to be made through a continuously rotating joint. We generally fit these to the pan axis which enables the remote heads to rotate continuously whilst still being fully connected. Some circuits are provided via the 15way Dplugs on the heads and base. Others are used internally for power, data and picutures. Our systems can pass the HD signal throught the slip rings to provide HDSDI or SDI directly from the base.
Up to 99 remote heads can be operated on a single system with up to 4 controllers and 4 engineer positions. These can be a mixture of cameras and remote heads. We manufacture protocol converters for many camera types and also for other types of remote heads. Our Multi Camera Selectors and Data Multiplexers take care of operator priorities and can be set to the user’s preferences for timeouts etc.
All cables have a resistance to current passing along them. This resistance causes a voltage drop along the cable which is directly proportional to the current being drawn: i.e.. the power consumption of the equipment.
The voltage drop can be calculated by the formula:
V = I x R. Where V=voltage drop, I=current, R=resistance.
You need to add twice the quoted resistance per metre because you have to add the power and the Ground conductor together which is the complete circuit.
So, for our typical heavy duty XLR4 - XLR4 cable the resistance is quoted as 40 ohms per kilometre, per conductor.
For 100m this is 0.8ohm for both conductors together. Our cameras typically draw 1 Amp.
Using the formula above: Voltage drop = 0.8 x 1 ........ = 0.8volt. Make an allowance for other losses and you have a drop of 1 volt per 100m per camera.
This assumes you are using heavy duty cable. Thinner cables could have up to 3 times the resistance and loose 3v per 100m per camera.
If you run 2 cameras on a cable, the current draw and therefore the loss, is doubled. However you can roughly work out what voltage you need to put in to get the right amount of voltage at the far end.
It’s also worth bearing in mind that measuring the voltage at the far end of the cable is meaningless unless you have the camera, or dummy load, connected. Without the cameras connected a voltmeter will read the same voltage as is put in at the supply end. This is because voltmeters use virtually no current at all.
This means that when you first connect the camera it will see the full voltage until it draws current and the voltage decays. This is why our cameras need to be able to cope with a larger voltage for a short time.
4 cameras on a thinner cable with twice the resistance as above.
Twice the loss x 4 cameras = 8v per 100m. Therefore to get 12v at the far end with all cameras running you need to put in 20v.
All this assumes that your power supply can supply enough current. Although the cameras draw 1A, the losses may account for 30% of the power. So for 4 cameras you would need at least a 6A supply
Our standard power supplies deliver 3.4A @ 15v.
We also offer a high power supply which delivers 6A @ 15v. This can run 4 cameras at 50m on a voltage of 13v. with our heavy duty cable.