GENERAL DESCRIPTION The AH 2500A Ultra-Precision Capacitance Bridge is an extremely accurate and stable instrument used for precise measurement of capacitance and loss. The unparalleled accuracy and stability is derived from the use of a carefully designed ratio transformer coupled with an extremely stable fused-silica standard capacitor that is contained in an internal temperature-controlled oven. Measurements are made automatically, eliminating the cumbersome manual balancing previously associated with precision capacitance measurements. The bridge can be operated as a stand-alone instrument from the front panel controls. It can also be operated remotely from either of the built-in RS-232 or GPIB remote device ports. The AH 2500A is also available in an Option-E version which offers higher precision and significantly enhanced calibration and verification features. APPLICATIONS OF THE BRIDGE The AH 2500A Ultra-Precision Capacitance Bridge is designed to meet the critical requirements of the calibration and research laboratory, as well as those of manufacturing and incoming inspection where measurement precision is important. Some common applications are: • Calibration work including use as a transfer standard in primary and secondary laboratories. • Fuel gauge calibration. • Measurements at cryogenic temperatures. • Thermal expansion measurements for any type of matter, particularly metals, but also non-metals. • Liquid and vapor level measurements. • AC resistance measurements to 1000 teraohms. • Displacement and strain measurements. Very small changes in dimensions are measurable, approaching the diameter of an atomic nucleus. (This is less than a millionth of the wavelength of visible light.) • Quality and characteristics of any insulating medium (solid, liquid or gas). The presence of contaminating water is particularly easy to detect. See ASTM D150 and D924, • Research, development and production testing of capacitance or loss based sensors, • Measurement of pressures ranging from high vacuum to high pressure. There are many other applications to which the AH 2500A has been applied and to which it could be applied. Measurement Features • Fully self-contained — no external standard or other apparatus required for three-terminal measurements • Three-terminal BNC connections minimize connector costs and number of cables • Two-terminal measurements of any ungrounded device • Commutation (test signal reversal) to minimize external power line or other periodic signal pickup • Autoranging — one button or command takes all measurements • Selectable measurement time to optimize speed vs. noise trade-off • Test voltage is settable to an upper limit • Deviation measurements of capacitance, loss, or both, expressed in absolute numbers or as percentages • Zero correction of test fixture capacitance and loss • DC bias may be externally applied up to ±100 volts • Tracking mode can be entered automatically for unknown impedances that start changing rapidly • Units of loss are reportable as conductance, dissipation factor, or series or parallel resistance