Patent ID: 7991568

Claim:
A digital multimeter for automatically selecting measurement functions comprising: input terminals of a measured object; an analog/digital conversion circuit; a microprocessor; a potential divider network; an electronic switch; a display; and a fast analog/digital converter; wherein, said fast analog/digital converter is connected to said input terminal of the measured object by said potential divider network to obtain a fast measurement of the voltage between said input terminals; said analog/digital conversion circuit inputs said fast measurement of the voltage into said microprocessor for analysis and processing, said microprocessor controls said electronic switch to switch said potential divider network by including additional resistances into said potential divider network and choose a measuring range for the fast analog/digital converter; said microprocessor controls an auxiliary program-controlled voltage and current source in connection with the input terminals of the measured object and, according to a result of voltage variations by said fast analog/digital converter, choose a measurement method and the measuring range for the fast analog/digital converter; when said auxiliary program-controlled voltage and current source is actively applied to the measured object at the input terminal, the connection between said program-controlled voltage or current source controlled by the microprocessor and said input terminal is cut off; when said auxiliary program-controlled voltage and current source is passively applied to the measured object at the input terminal, the connection between the said program-controlled voltage or current source controlled by the microprocessor and said input terminal is connected; said microprocessor controls the display to show a measured value.