Remote Positioning Devices
There are two main types of remote positioning device, those that move only in a horizontal plane, and those that can move in two planes. Movement in a horizontal plane is known as panning or scanning. Movement in the vertical plane is known as tilting. The device that provides movement in both planes is called a pan, tilt unit or pan, tilt drive.
Both scanners and pan, tilt units are made for indoor and outdoor use. The construction is fundamentally the same except that those units for external use are designed for the appropriate IP rating. (See Chapter 9 for description of IP ratings). Pan, tilt units are also produced for the range of hazardous environments mentioned in Chapter 10.
A common type of scanner is shown in Diagram 11.1, which may be designed for either internal or external applications.
The camera may be mounted directly on the platform in usual indoor situations. The camera mounting platform is adjustable to a fixed position of tilt by a bolt through the pivot. The degree of rotation is set by two movable strikers that operate limit switches at each end of the required travel. These units can be set to automatically reverse when a limit switch is operated and therefore continuously scan between the set limits. This is called auto-pan and requires an additional simple board in the control unit. The wiring is very simple and telemetry would not generally be used for controlling this type of device.
For external use the units are larger and made weatherproof to the appropriate standard. They are also more powerful than indoor models because they need to support a weatherproof housing. The camera supply and coaxial cables must be left with sufficient slack to eliminate strain through the movement of the scanner. There should be enough slack cable to allow for the maximum travel of the unit. Although it may be initially installed with a small degree of scanning, requirements could change in the future.
Typical scanning speed is 6° per second and maximum rotation in the order of 345°. There is usually a minimum rotation of 5°-10° due to the size of the limit stops.
This type of scanner is not very attractive in appearance especially with the slack cables going to the camera. On the other hand it is easily seen and is often used for its deterrent value. Where aesthetics are important or discrete mounting is needed there are other types of scanners available. The hemispheres and domes mentioned in Chapter10 could incorporate scanning drives.
Pan, Tilt Units
As with scanners, pan, tilt units may be designed for either internal or external use. There are two main types of pan, tilt unit. The first is a unit where the camera or housing is mounted directly on a platform that forms part of the construction. There are two types of this design where the platform is either mounted on the side of the unit or over the top. The second type of pan, tilt unit is where the driving components are contained within an enclosed housing.
Rating of Pan, Tilt Units
Pan, tilt units are rated by the load carrying capacity of the platform. In addition, over the top units are rated by the centre of gravity of the load being within a certain distance above the top of the platform. See comments later for load rating of over the top units.
This article is an extract from chapter 11 of 'The Principles & Practice of CCTV' which is recognised as the benchmark for CCTV installation in the UK.