The card contains 2 circuits, between A/COM and B/COM. Each input receives a square voltage 200Vpp. After passing through a serial resistor 1k, another input is created. 3 voltage dividers based on high impedance resistors lower the voltages to reach imput range of the instrumentation amplifiers (IN 2331 dual amplifiers). These instrumentation amplifiers are used to scale the voltage differences to the range 0-5V wich will be send o the A/D entrance of a simple microprocessors.