Abstract: An instrument for measuring a gap between it and an opposing surface, comprising a gas conduit having an inlet and an outlet, a sensing orifice in the outlet, a gas pump connected to the inlet for applying an alternating pressure to the gas conduit so that puffs of gas are directed from and drawn back to the sensing orifice. A sensor is in fluid communication with the conduit responsive to a physical property of the gas responsive to a condition determined by the gap size and a circuit is responsive to the sensor to provide a signal respective to the physical property.

Abstract: An ultrasonic imaging system probe with an even-number of transducer elements, has a transformer for coupling the received signal from each transducer to an associated cable. The polling of the transformer primary windings are identical while the polling of the secondary windings of the transformer alternate, i.e. are reversed for all even-numbered channels, with respect to odd-numbered channels. All odd channel outputs are conected to a first signal bus, while all even channel outputs are connected to a second signal bus. The signal busses are connected to inputs of a differential-input amplifier, having an output which provides the sum of all channel transducer outputs, with suppression of any common-mode signal appearing in the system from the channel transformer secondary windings to the differential amplifier inputs.