DIGITAL VIDEO RECORDER (DVR) GUIDE
DVR
Digital Video Recorders (DVR) come in many levels with varied functions from the very basic simplex models to highly sophisticated units. All record to hard disks, as found in a computer, so there is no requirement to change and store tapes. There are many different functions available (listed below) and it is very much deciding which is the most important functions to have and choose an appropriate model.
The most important issues to consider when choosing a DVR are:
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Channels - one channel is required for each camera in the system, 8 channels will provide enough space for 8 cameras. Consider future requirements with a few spare channels. A typical DVR has 4, 8 or 16 channel.
Frame rate - shown as Frames Per Second (FPS) or Images Per Second (IPS). 25 FPS is the equivalent to real time so this needs to be per channel to provide real time on each camera, therefore, to ensure real time a four channel DVR should have a frame rate of 100 FPS.
Hard Disk space - there is a considerable choice on the size of Hard Disk available from 160Gb to Terrabytes. Some of the basic DVRs are limited to the amount of Hard Disk space they can have but most DVRs can accept enough space to ensure an acceptable recording time. The actual maximum recording time is very much dependent on the model, the amount of cameras on the system and how it is set up. Some models can have a Hard Disk Array added to extend the amount of space available.
Resolution - picture quality is dependent on several factors, some of which can be adjusted on the DVR, but the resolution should be of reasonable quality as a start. A resolution of 352 x 288 pixels is accepted as "good quality" with 704 x 576 pixels being "high resolution. Some DVRs have the ability to record at higher resolution but there is an offset with the high use of Hard Disk space.
Evidence Retrieval/Backup - at sometime you will need to provide evidence to the police/authorities or backup incidents to a storage. Most DVRs have an integral CD or DVD writer which allow for easy transfer of incidents, some also have a USB socket which allows for the connection of a pen drive or external hard-drives to backup evidence. Basic models usually have a connection for an external device but no integral device so an external device would be required for evidence retrieval.
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There are many different functions available some of which are listed below with brief explanations:
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Networking/Internet Connection - allows monitoring/control over a network or broadband internet connection (requires a static IP address) becoming popular with businesses that have more that one premises.
Motion Detection (also called Event Recording) - the DVR can be set to record on the detection of movement which will save disk space.
Infra-Red Remote Control - for ease of operation a remote control is provided.
Audio Recording - records audio on some channels (will use hard disk space).
Alarm inputs - allows for the connection for alarm signals from cameras.
Control of PTZ cameras - allows for the control of PTZ cameras without the requirement for additional equipment.
Call Monitor - allows for the connection of a second monitor, note this may be limited compared to the main monitor.
Digital Zoom - will magnify the picture on the screen digitally.
Snapshot - allows a still picture to be captured.
Schedule Recordings - allows the DVR to record at specific times only.
Recording Speed - allows the change of Frame Rate in order to save Hard Disk space.
Covert Camera Setting - allows a channel to be hidden on the display.
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