Understanding Time Lapse Video Recorders

From CCTV Information

Today, VCRs are considered a mature technology - having been commonly used in a domestic capacity since the early Eighties. Security VCRs, although appearing the same in product design as domestic recorders, have a number of additional features specifically for use in the Security Marketplace. They require an "industrial chassis" which offers increased durability, tailored to take the additional stresses and wear and tear expected when using a VCR continuously rather than the typical 3-4 hours per day in which a domestic machine may be used.

The principal functional difference is the ability for a Security VCR to record for at least a 24 hour period. This is achieved as information is taped periodically rather than continuously (as in domestic recordings). Ultimately, this allows your VCR to step camera recordings (using standard video cassettes) over much longer periods of time. This has been proven as an extremely successful method of surveillance monitoring, both in terms of required footage, albeit that there is a trade-off between the requirement for extended recording, and cost efficiency.

The way in which time-lapse recording works in practice is best explained by example. A standard domestic VCR records continuously in real-time, with 25 frames per second, 2 fields per frame (a total of 50 images in all). An industrial machine, on the other hand, has selectable recording intervals, allowing you to reduce the amount of information you tape depending on your requirements. If the record rate is dropped to 8.33 frames per second (16.66 images in total), for example, the VCR can span recordings to 24 hours worth of information. In this instance the VCR is said to be running in 24-hour time-lapse mode.

As the recordings in time-lapse mode are periodic rather than continuous, there is a loss in the information taped in any single sequence (dependent on the settings), that can give a stroboscopic effect on replay. Consequently, the configuration of time-lapse recording is very much dependant on the practical needs of the particular security installation.

It should also be borne in mind that when Time Lapse VCRs are used in conjunction with Multiplexers the frames recorded will be divided between the number of Cameras being viewed. The following table gives an indication the gap between frames being recorded, per Camera, relative to the number of Cameras.

	24hr RT	24hr TL	72hr	168hr	960hr
1 cam	0.06sec	0.18sec	0.50sec	1.14sec	6.42sec
4 cams	0.24sec	0.72sec	2.00sec	4.56sec	25.68sec
8 cams	0.48sec	1.44sec	4.00sec	9.12sec	51.36sec
12 cams	0.72sec	2.16sec	6.00sec	13.68sec	77.04sec
16 cams	0.96sec	2.88sec	8.00sec	18.24sec	102.72sec

This article was supplied by Norbain and used with permission. Norbain are manufacturers of the Vista Protos range of state-of-the-art products designed for leading edge and performance critical applications - where extensive features and functionality are the key.