2.1.8 Pulse Bistable Relays
Pulse bistable relays are small electromechanical devices, which have the ability to open and close
their contacts in a preset sequence. Although they are called “relays”, their operation principle, con-
struction, external form, and dimensions are quite different from that of the standard relays described
in Section 2.1.1. Their use in automation systems is limited, but in the cases where this is required,
it facilitates immensely the implementation of an application. A pulse bistable relay consists of a cam
mechanism, an electromagnet, and the electric contacts as shown in Figure 2.12. The cam is a double
ON button
OFF button
Set coil
Reset
coil
Reset
coil
(a)
(b)
Pivot
R
N
R
N
Power
contact
Power
contact
ON button
OFF button
Set coil
Pivot
Latch
state
Release
state
Figure 2.11 Schematic diagram of latching relay: (a) relay tripped and power circuit open, and
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