The DB-24P is a 24 channel isolated digital input daughter board for DIO24,DIO48,DIO144 ,PIO-D144,OPTO-22 Compatible digital input board or any 722,724, digital input board . The optically isolated inputs of the DB-24P consist of a bi-directional opto-couple with a resistor for current sensing . You can use the DB-24P to sense DC signal from TTL levels up to 24V. You can also use DB-24P to sense a wide range of AC signals. The DB-24 P registers a constant logic high if the frequency of the input AC signal is greater or equal to 1 kHz, and if the voltage of the AC signal is at least 4Vrms. If you are using AC input signal ,you must short the AC filter Jumper. You can use the board to isolate the computer from large common-mode voltages ,ground loops, and voltage spikes that often occur in industrial environments.