Abstract: Circuitry for use in a voltage measurement and display device provides automatic function change for measurement of AC or DC voltages. Voltage measurement in a predetermined mode (DC, for example), is assumed. Upon detection of an input voltage component exceeding a predetermined threshold of the other mode, (AC, for example), the measurement function is changed to that other mode. Upon detection of a component in the other mode, in a range between the predetermined threshold and a second (preferably lower) threshold, an annunciator is activated to alert the user to the presence of the other mode (AC) voltage, for manual activation of a function-selecting switch if desired. Thus, in a specific embodiment, automatic function changeover is provided upon detection of AC components exceeding a predetermined threshold, along with activation of an AC annunciator.

Abstract: A digital multimeter having a tone generating circuitry and operable in a tone mode of operation for providing an audible indication when a measured electrical characteristic has a predetermined relationship with a reference value. The audible indication may be provided when a voltage level exceeds a preselectable limit, such as 1 or 2 volts. Predetermined limits for resistance values may also be selected for actuation of the audible tone. The device may be utilized as a conventional multimeter when the tone mode is non-operative.