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