The Model 8922A is a Digital True RMS Voltmeter, capable of accurately measuring the true rms value of nonsinusoidal signals containing AC or AC + DC components. The instrument has a frequency range of 10 Hz to 11 MHz with a full-scale crest factor of seven, and is capable of displaying measurements in either volts or dB units. Selecting the VOLTS position on the dB/VOLTs switch enables the volts display mode and two applicable front panel annunciators (V, mV). In this mode, the instrument displays up to a 3lA digit figure to indicate the true rms value of any AC or AC + DC input signal whose amplitude is between 180µV and 700V rms (1000V peak). The dB display mode (logarithmic) is enabled when dB is selected on the front panel dB/VOLTS display switch. In this mode, the instrument displays up to a 4l/i digit dBm value of the input signal referenced to one-of-twelve manually selected impedances (50 to 1200 ohms). The dB display mode also uses two annunciators — dB and RELATIVE REFERENCE — and to establish the instrument’s operating status. The RELATIVE REFERENCE annunciator lights whenever the REL switch is depressed to indicate that any further dB measurements will be referenced to the voltage present at the time the switch was pressed. An UNCAL annunciator lights with both display modes when internal protection circuits are energized. When AUTO is selected on the AUTO/HOLD switch (the out position) the autorange mode selects one-of-seven input ranges to optimize the display resolution. Complementing the instrument’s high digital resolution is an analog panel meter for use in applications that require peaking or nulling. This meter does not have calibration markings since it is intended for peaking and nulling indications only. Note that the 8922A accomodates floating measurements up to approximately 0.6V peak with respect to earth ground. Isolation of 0.6V peak will accomodate the few hundred millivolts of typical common mode voltage. Full operator protection is maintained since — under fault conditions — the diode isolation circuitry conducts to insure that the common mode voltage is never greater than one diode drop.