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a control device that, after a predetermined time interval, automatically starts or stops a system, machine, or apparatus used in industry or the home. The term “timer” is also applied to a monitoring device that signals when such a system, machine, or apparatus is to be started or stopped. Depending on the principle of operation, a timer can be mechanical, hydraulic, pneumatic, or electrical. The time interval of a timer is usually predetermined in the same way as in a timing relay.
Timers are classified as single-shot, multishot, and repeat-cycle. In single-shot timers the time interval is usually set manually, for example, by moving the hand of the time indicator. In this case, the timer mechanism is simultaneously wound, and the timer will operate when the hand returns to zero. Multishot timers automatically operate several times with preset time intervals. Repeat-cycle timers operate with the same time interval (the period of the cycle) after equal periods of time. In multishot and repeat-cycle timers the sequence of time intervals, or the timer schedule, is prescribed by such means as a punched tape, a disk with pins, or a system of shaped cams.
Timers based on clocks have the highest accuracy and reliability, as well as the broadest range of time intervals. Clockworks are used mostly in single-shot and multishot timers designed for operation within a 24-hour period. Electric and electronic time measurement devices are used mostly in repeat-cycle timers that function continuously over periods of several months.
B. M. CHERNIAGIN
a circuit used in, for example, radar sets, television equipment, and telecommunication systems primarily for the purpose of ensuring that certain processes occur in conformity to certain time relationships.
In radar sets, for example, timers provide synchronization of such processes as the emission of radio signals by the transmitter, the blocking of the receiver during transmission, and the starting of indicator sweeps at the instant the signal is received. In telemetry systems, multichannel pulse communication systems, and other information systems, timers provide a fixed spacing between, for example, information-carrying symbols (in digital transmission) or word or address markers.
The main component of a timer is a generator of frequency-stable oscillations, such as a quartz-crystal oscillator or a maser. The oscillations are used for such purposes as synchronization or the provision of local time markers either directly—that is, in the form they are taken from the oscillator output—or after conversion to other oscillations (or pulses) that are characterized by certain altered parameters, such as frequency, phase, or amplitude. In the case of pulses, the characterizing parameters include pulse duration and shape.
A. F. BOGOMOLOV