Figure 2-82. - Types of sending units for pressure gauges.

Figure 2-83. - Types of temperature gauge sending units.

SPEEDOMETER AND TACHOMETERS

Speedometers and tachometers in some form are used in virtually all types of self-propelled equipment. Speedometers are used to indicate vehicle speed in miles per hour (mph) or kilometers per hour (kph). In most cases, the speedometer also contains the odometer which keeps a record of the amount of mileage (in miles or kilometers depending on application) that a vehicle has accumulated. Some speedometers also contain a resetable trip odometer so those individual trips can be measured.

A tachometer is a device that is used to measure engine speed in revolutions per minute (rpm). The tachometer may also contain an engine-hour gauge which is installed on equipment that uses no odometer to keep a record of engine use. Speedometers and tachometers may be driven either mechanically, electrically, or electronically.

Mechanical Speedometers and Tachometers

Both the mechanical speedometer and the tachometer consist of a permanent magnet that is 2-56