Tachometer
A tachometer is the device that shows engine speed in rpm; it takes its signal from a magnetic pickup, from the alternator W terminal or from an optical reflection. On panel-type tachometers the number of pulses per revolution is adjustable, so this parameter has to be set according to the engine for a correct reading.
For someone installing an electronic throttle kit, the tachometer is more than a measuring instrument: it is the only objective proof of the adjustment made. The potentiometer position or the stored point does not tell you a speed; the tachometer does.
- Calibration: the panel tachometer is verified by comparing it with an independent handheld optical tachometer. If there is a deviation, the pulses-per-revolution parameter is corrected.
- Use: idle, work speed and the upper limit are determined by reading them from this instrument; the drop under load is also followed from here.
The GS740 and GS740-3P have no speed display on the kit; these kits do not read speed. For that reason, in an installation requiring constant speed, having a separate tachometer is in practice mandatory. On a generator an alternative route is to verify 50 Hz with a frequency meter; on a 4-pole alternator that means 1500 rpm.
Context in which this term is used: Electronic speed and throttle control on diesel engines