The electrical output from sensors such as thermocouples, resistance
elements used for temperature measurement, strain gauges, diaphragm
pressure gauges, LVDTs, etc. is in analogue form. An analogue signal
(Figure 1.37(a)) is one that is continuously variable, changing smoothly
over a range of values. The signal is an analogue, i.e. a scaled version, of
the quantity it represents. A digital signal increases in jumps, being a
sequence of pulses, often just on-off signals (Figure 1.37(b)). The value
of the quantity instead of being represented by the height of the signal, as
with analogue, is represented by the sequence of on-off signals.