a device that records the operating time of an engine, machine, or mechanism; it is used to monitor and log the service life of the engine.
The main components of an engine-hour meter are an indicator of the engine’s operating conditions, which records such data as the speed of rotation of shafts, the temperature of exhaust gases, or the torque; a timer; and a recorder, usually a mechanical counter with digital drums. Electric clocks, or semiconductor or magnetic devices driven by a constant-frequency quartz or other master oscillator, may be used as timers for aircraft engines. The simpler engines of tractors and harvesters have indicators that are driven mechanically by the engine shaft through a reduction gear. In this case, the hours of operation are determined from the number of revolutions of the engine. Self-winding spring driven clocks are also used as timers for such engines.