2.0 OVERVIEW
2.1 INTRODUCTION TO TIME-LAPSE RECORDERS
Time-lapse recording permits longer than ordinary recording times. The primary reason for using time-lapse recording in a CCTV security system is that a single VCR tape can be used for an extended period of time beyond the standard record- ing time. The following explains how time-lapse recording works.
The actual recording on VCRs is a series of still pictures or fields. Standard con- sumer VHS recorders store 60 fields (30 frames) per second. A T-120 cassette lasts just two hours in this mode (SP mode). You can get slightly longer recording times (six hours) using the extended recording mode (EP mode). You can record even longer on a T-160 cassette in these modes: two hours and 40 minutes in SP mode and eight hours in EP mode. (Refer to the table in Section 8.1.1 for actual recording times in different modes.)
Time-lapse VCRs, however, use microprocessor-based techniques to record fewer fields per second than a normal VHS machine and extend recording time. This negates the need to change the tape every two hours—and also substantially re- duces viewing time when the recording is played back, another important consider- ation.
In normal VCR operation, all video head scans (60 per second) are recorded. But in time-lapse mode the tape runs more slowly and records pictures periodically. In 12- hour mode, a normal time-lapse machine records 10 fields per second, and in 24- hour mode, it stores just five fields per second (for up to 12 and 24 hours on a tape, respectively). Longer times are possible by slowing the recording rate further.
At normal speed a picture is recorded every 1/60 of a second so there is little change over five frames. In longer time-lapse modes, however, a field is recorded intermittently over a longer period of time so changes are apparent from field to field.
The time-lapse recording can be played back at normal two-hour tape speed, which makes for rapid review—one of the time-lapse recorder’s most important advan- tages. Action on the tape, however, appears faster than normal.
As an advanced feature, time-lapse recorders (like the TLR2168S) can automati- cally switch from time-lapse to real-time recording when an alarm condition occurs. This is important since the primary purpose of recording an event is identification, and real-time recording provides more detail.
2.2 TLR2168S FEATURES AND FUNCTIONS
The TLR2168S time-lapse video recorder is a powerful surveillance tool designed for industrial and security recording. In addition to ordinary two-hour (SP – standard play) and six-hour (EP – extended play) recording modes, its time-lapse modes permit recording of 18, 24, 48, 72, 96, 120, or 168 hours. (Linear modes are desig- nated as L18H and L24H.) You can extend recording up to 64,800 hours (for T-120 tape) using one-shot recording with a three-minute time interval. The TLR2168S features frame-by-frame playback and high-speed playback of longer recordings. It is a six-head machine that can play back tapes recorded on virtually any VCR.
Audio Recording–Audio recorded in 2H, 6H, or L(inear)18H, L24H mode is played back only in its respective mode.
Resolution And Image Quality—This VCR has a high-quality circuit allowing more than 330 lines in B/W (black and white) recording and more than 300 lines in color recording in normal VHS mode. S-VHS ET and S-VHS mode resolution is even higher at more than 400 lines.
S-VHSMode—This mode has higher resolution and picture quality than normal VHS mode when using S-VHS tape (over 400 lines).
