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Video Recording Equipment
(Chapter 2   Video Surveillance, Continued)

Time-lapse recorders

Time-lapse recorders have the ability to incrementally record at specific time intervals, recording a single field or frame of video information with each increment. In the 2-hour (real time) recording mode, a video recorder is recording 60 fields or 30 frames of video information each second. To determine the time interval between pictures recorded at specific speeds, the following formula can be used (based on using a T120 tape at 60 Hz):

Table 9

Because the tape is slowed down in the time lapse mode, and the video heads record only specific fields of information, some actions are easily lost. If a tape recorded in real time (2-hour) was compared to a tape recorded at a 240-hour speed, there would be lost information between them. The slower the tape speeds during recording, the more information that can be lost. Exhibit 2.17 presents recording intervals for various recording tape speeds.

Exhibit 2.17

There are some low-priced time-lapse recorders (approximately $500) on the market today, but dependability and resolution may be sacrificed if an industrial-quality recorder with at least 400 lines of resolution (approximately $1,200-$2,700) is not specified. A high-resolution camera and monitor may be used with good results during realtime viewing, but if the playback tape has been recorded with a standard time-lapse recorder with low resolution, the results may be disappointing. For best results, a high-resolution industrial-quality recorder should be used.

 



Research Report:   The Appropriate and Effective Use of Security Technologies in U.S. Schools