Using the circuit shown in Figure 1, the relay is closed briefly when S1 is pressed a sensor is activated). The time interval in which the relay is on depends on the capacitor value and the resistance of the relay’s coil. The time constant of the circuit is measured from the instant in which S1 is pressed to the point at which the voltage in the coil falls to the minimum that keeps the contacts closed (holding voltage). Relays between 470 and 4,700 µF can be used in common applications.
Figure 1 – Short-action Relay
