A digital multimeter is composed of a function converter, A/D converter, LCD display (liquid crystal display), power supply and function/range conversion switch. The A/D converter generally uses the ICL7106 double integrating A/D converter. . ICL7106 adopts two integrations. The first time is to integrate the input analog signal V1, which is called the sampling process; the second time is to integrate the reference voltage - VEF, which is called the comparison process. The two integration processes are counted through a binary counter, converted into digital quantities, and displayed in digital form. To measure AC voltage, current, resistance, capacitance, diode forward voltage drop, transistor amplification coefficient and other electrical quantities, a corresponding converter must be added to convert the measured electrical quantity into a DC voltage signal.