An example use could be for detecting a broken timing belt drive, in order to stop the motor of a machine to prevent damage. (Stop after approx. 3 seconds).
A sensor would be looking at the teeth of the driven pulley. The sensor is represented by the two logic sources at the bottom left. The upper one is normal operation (sensor sending a pulsed signal). The lower one is a failure situation (sensor sending a static signal, either high or low).
The logic source at the top left is causing the counter to count up. If the counter reaches 4, it will cause the relay for the motor to drop out. The pulsed signal from the sensor is constantly resetting the counter, thus preventing it reaching 4. If the pulse stops (switch in lower position), the counter will reach 4.
