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CCTV Suppliers FAQ

CCTV Suppliers FAQ

 

What does CCD stand for?

CCD is an abbreviation for Charge Coupled Device. The CCD is the image sensor of the CCTV camera. The lens focuses reflected light onto the surface of the CCD chip and photo diodes within the chip produce an electrical charge proportional to the amount of light falling onto them.

 

What does DSP stand for?

DSP stands for Digital Signal Processing. In a Digital Signal Processing CCTV camera digital circuits carry out signal processing as opposed to analogue circuits. The electrical signals which the CCD chip produces are linked to an analogue to digital converter and brightness level reference points are assigned numerical values. The digital signal processor inside the camera processes these values and produces the video signal.

 

Do I have to use a Regulated Power Supply?

In general the answer is yes. Most manufacturers will recommend the use of such power supplies as standard with their equipment. You should always consult the manufacturer’s specifications prior to the connection of any power supply.

 

What is an IR cut filter?

Colour CCTV cameras use a filter mounted on top of the CCD chip which is known as an IR cut filter. The colour cameras use this chip as the spectral response of the CCD chip is quite different to that of the human eye. The filter makes the spectral response closer to that which would be perceived by the human eye. The IR cut filter can affect the sensitivity of the camera at night and therefore True Day and Night cameras have been developed which either have no IR cut filter or a motorised IR cut filter which moves out of the way of the CCD chip at night.

 

What does TVL mean?

In the context of a CCTV camera TVL (TV Lines) refers to the horizontal resolution (the maximum number of vertical lines the camera can resolve) of the CCTV camera.

 

What do the IP ratings of your cameras mean?

Camera housings come in various shapes and sizes. With regard to the correct IP rating protection, this will range from dust and water ingress. This system is governed by a number of European and British standards.

IP55

  • Protected against dust – limited ingress.
  • Protection against low pressure jets of water from all directions – limited ingress permitted.

IP65

  • Protection against dust – no ingress.
  • Protection against low pressure jets of water from all directions – limited ingress permitted
  • Protection against high pressure water from all directions – limited ingress permitted.

 

What do the lens sizes of CCTV cameras mean?

The Cameras we sell have different focal length lenses which are expressed in millimetres. The smaller the number, the wider angle the lens. A 4mm lens is very wide angle (on a 1/3″ CCD Chip, roughly 62 degrees horizontal viewing angle), whilst as we move up to 6mm the angle closes in and the image appears nearer. If you are not sure what focal length you require, you could choose one of our Vari-Focal CCTV cameras.

 

What are OSD cameras?

OSD (On Screen Display) cameras have a menu system within the camera assembly that can be accessed in order to set functions such as Iris levels, AGC on/off and most features of standard and advanced cameras.

 

What is the difference between Auto Iris and Direct Drive Lenses?

An Auto Iris lens is one that automatically adjusts its iris for changes in the scene lighting levels. The motor that opens and closes the iris is driven by an Amplifier that processes a small electronic signal changing with the light level.

A Direct Drive ‘DD’ lens does not have this Amplifier and can only operate with a camera fitted with one. A camera specification will indicate the available output options.


Does the ‘f’ stop matter when choosing a lens?

Yes, lenses are usually specified as having a minimum and maximum ‘f’ stop rating; the ‘f’ stop is a measure of how efficiently the lens allows light from the scene, to pass through the lens and onto the camera CCD sensor. The maximum aperture (when the lens is fully open), is the minimum ‘f’ stop number and the minimum aperture, (just before the lens completely closes) is the maximum ‘f’ stop number.

A low minimum ‘f’ stop number means that the lens can pass more light through during dark conditions, which will produce better pictures at night.

A high maximum ‘f’ stop number may be necessary where there is a high level of light or reflection. This will prevent the camera ‘whiting out’.


What is the difference between simplex and duplex multiplexers?

Video multiplexers are designed to allow recording of several cameras onto one recorder.

Simplex

A simplex machine is best suited to applications where recording only is the priority. Simplex machines cannot display multi screen images (i.e. quad, 9 way and 16 way split) while in the record mode.

Duplex

If an operator is monitoring the system (i.e. security guard) then a duplex machine is more suitable. A duplex machine can provide screen splits and user selectable images without affecting what is recorded onto the recorder. Should you use two recorders, it becomes possible to record and playback simultaneously.

 

What is a ground loop?

An AC current that can be produced in a cable. This is usually caused by parts of the system being fed from different electrical sources resulting in different earth potentials at each end. The result is interference on the signal, usually in the form of dark bands across the monitor and on occasion tearing in the top third of the image.

 

How can I eliminate ground loop faults?

This can be achieved in a number of ways, the easiest of which is the installation of a Ground Loop Isolation Transformer. "HumBlock" This is best installed at the monitor or recording end of the system.

CCTV Suppliers Australia PO Box 4360 Langwarrin, 3910 Melbourne Victoria T: 0401 051 694