The Model 72AD Capacitance Meter provides instant, direct-reading, three-terminal and differential capacitance measurements from 0.05 pF to 2000 pF. This capacitance coverage is divided into four ranges, selected by panel push-buttons or remotely. These are arranged in a 2, 20, 200 and 2000 pF full-scale sequence. (1) The digital display provides 3 digits plus one readout, decimal point, and + or - Indications. The solid-state design and the low-level crystal-controlled signal source contribute to the high stability and excellent reliability of the instrument. The measurement of semiconductors Isfacilitated by the 15 mV rms level of the 1 MHz test signal, and by the provision for applying up to 600 volts of dc bias to the test specimen. Bias voltage, of either polarity, may be applied to either or both sides of the specimen . The Model 72AD employs an unusual range-switching system using switching diodes and miniature reed relays; the elimination of the switch contacts from the measurement circuits assures a maximum of reliability and stability. The phase-sensitive detection system permits the measurement of even low-Q devices (down to Q =1) without sensibly degrading the accuracy of the measurement. Two plug-in test connection adapters are supplied with the Mode! 72AD. One of these, fitted with two sets of coaxial connectors, Is Intended for use with coaxial cables and remotely located test fixtures for both three-terminal and differential measurements. The other adapter, with two terminal posts, is used for wire-lead type components; differential measurements are not possible with this adapter. Both linear dc and binary coded decimal outputs are available at rear-pane! terminals and at the appropriate pins on the rear edge connector. These two features extend the range of applications beyond ordinary laboratory measurements to include production testing and integration into a controlled test system, using logic-level programming. Remote ranging is controlled by grounding the EXT PROG terminal on the rear edge connector, disabling the front-panel range switches. Grounding anyone of the four range- line terminals will then select that range. Connection to the edge connector should be made with an Amphenol Type 225-22221-1 01 plug, or equivalent.