Global Risk Solutions

Passive infrared detection exploits the fact that all matter at temperatures above absolute zero radiates energy.

This radiation is distributed across a continuous spectrum of frequencies in a characteristic pattern, where the highest frequency is determined by the temperature of the source.

The amount of energy is highest at the highest frequency and decays towards
zero at lower frequencies. For example, extinct stars (which are very cold) can only be detected with radio telescopes, as they only radiate at these low frequencies, while active
stars (like the sun) are very hot and radiate beyond the visible spectrum.

The peak transmission for the human body temperature lies in the far infrared region at about 10 micrometers, or 30,000,000,000,000Hz. The sensors used to detect this radiation are made of pyroelectric material, usually lithium tantalite. It is formed into a thin wafer with an area of about 1 mm by 2 mm. Electrodes are attached top and bottom and it is mounted inside a housing, which contains a window with an optical filter.

Any radiation impinging on the exposed surface of the sensor will produce a local temperature rise, resulting in a voltage across the electrodes. Because of the nature of the signal high impedance buffer and a high value resistor are generally also built into the housing.

In security applications motion detection is required and therefore a dual sensor is usually used. Two identical sensors are mounted side by side inside the housing, but electrically connected together with opposing polarity. This has the advantage of canceling the steady radiation from all objects in the field of view, while the image of an object of different
temperature moving across the two sensors consecutively produces a signal
of positive and negative polarity. The large field of view of the sensors necessitates the use of some form of focused optical system. Ideally, for optimum detection, the projected image of the target at maximum range is about the same size as the sensor. The
fulfillment of this requirement however results in a very narrow field of view. For most security applications this is unacceptable, as it leaves large blind sectors, which could easily be exploited by intruders. However, by using several projection systems, pointed both vertically and horizontally in different directions and different focal lengths dependent on viewing distance, not only coverage of a reasonable area can be obtained, but also an intruder traversing the area will produce multiple signals. Also, by selecting appropriate apertures for the projections a reasonably similar signal amplitude can be generated from an intruder, both close in and at near maximum detection distance.

For longer distances, a narrow corridor of detection is preferable, while zonal coverage with a number of "fingers" or projections from a large angular spread is normally used. The latter is limited to applications for short distances, as all the individual projections
are superimposed to form a composite signal. While only one projection at a time may produce a signal from an intruder, all the others are still looking at thermal variations in the environment, reducing the signal to noise ratio. This of course has a direct effect on the false alarm rate.

For undemanding applications a Fresnel lens is adequate as the projecting component. It can be easily and cheaply made, but because of its poor image quality it is unsuitable for large magnifications and therefore longer distances.

A faceted mirror is therefore the preferred device for longer distances, as it does not suffer from the limitations of the Fresnel lens.

 

 

Rapid Deployment Cameras offer a versatile and cost effective alternative to conventional CCTV systems.

For Police and Local Authorities, Portable cameras are a flexible tool against crime and disorder on city streets. Systems vary from fully functional PTZ and dome cameras to multiple fixed camera systems for wide area protection.

Where conventional static cameras fail to give adequate coverage of a moving crime problem, Portable systems can follow the crime wherever it goes. This is a flexible and cost effective weapon against crime migration and isolated disorder problems.

In the commercial sector, Portable systems adapt to a variety of surveillance requirements where for reasons of urgency, practical difficulty or budgetary limitations, the installation of conventional equipment is unsuitable or too costly.

What exactly are Rapid Deployment Cameras

Rapid Deployment Cameras are fully self-contained surveillance systems supplied with masts or brackets depending on the user’s requirements. With cable-free links for the transmission of video and telemetry over free air space, the equipment requires no costly wiring and may be powered from local mains or integral battery supplies.

Cameras may be monitored and recorded locally with our portable base stations or interfaced with existing networks for transmission to central monitoring stations.

Rapid Deployment Cameras also interface with our portable intruder detection equipment to provide complete area protection packages.

How they work

Conventional CCTV systems require cables to link cameras to a monitoring station. Video output and telemetry commands (to control the cameras are transmitted via the cables. Certain Rapid Deployment Cameras use radio to transmit video and telemetry over free air space and this is not only cheaper in certain circumstances but also allows the cameras to be moved around with greater ease.