Page 716 - Mechatronics with Experiments

702 MECHATRONICS

AC
input

AC input module

DC
input

DC input module

AC
output

AC output module

DC
output

DC output module
FIGURE 9.4: Opto-isolated input and output interface modules for two-state (ON/OFF,
conducting/non-conducting) devices: DC input, AC input, DC output, AC output types.

Relays electromechanical switches. It is the most commonly used electrical switch
in control circuits. It has two states, ON and OFF (Figure 9.6). A relay is used to connect
an electrical line with contacts. It is the electrical equivalent of a manually operated switch
in electrical circuits. It has two main parts:
1. contacts for connecting the main electrical circuit (to turn ON and OFF the main
line),
2. coil to operate the plunger mechanism that moves the contacts.
The basic operating principle follows that of a solenoid winding. A conductor winding
forms the coil. The control voltage is applied to the coil and hence develops a current
proportional to the control voltage and resistance of the winding. The coil then generates an
electromagnetic field. The plunger is pulled as a result of the electromagnetic field. When
the coil is deenergized, the electromagnetic force goes to zero and the plunger moves back
under the effect of a spring. In a relay, the plunger motion is connected to a mechanism so