Abstract: A pulse-echo ranging system is described employing a microwave transducer head (100) providing an echo profile output signal which is largely compatible with receivers (204) and echo processing systems (206) designed for acoustic transducers. The transducer head employs novel microwave pulse generators (20a, 20b) each utilizing a microwave cavity (20a, 20b) excited by an avalanche discharge through a small signal diode (D2a, D2b) initiated by avalanche of a driver transistor (TR1a, TR1b) by a trigger pulse. Repeated pulse from one generator (2a) are transmitted by an antenna (12) towards a target, and return are mixed with pulses from the second generator (26) which are subject to a progressively swept delay relative to the transmitter pulses. The mixer output is applied to a tuned amplified (110) to extract components at an alias frequency related to the sweep rate of the delay relative to the transmitter frequency. The aliased signal is passed to a receiver (204) and echo processing system (206).

Abstract: A portable interface unit incorporates a modem for connecting a personal computer through a bidirectional communication link to enclosed process control equipment by passing radiation, preferably infra-red radiation, through a casing enclosing the unit. The computer has a bidirectional digital serial interface specified in accordance with an industry standard, and the modem has a complementary bidirectional digital serial interface, an optical modulator and an optical demodulator, and a power supply. The power supply can be a circuit to derive power from the serial interface of the personal computer, or from a battery. The portable interface unit provides a versatile bidirectional communications link which is particularly suitable for use in hazardous environments and with electronic equipment designed to be environmentally sealed or tamperproof, and permits general purpose computers to be used to program, diagnose, configure or interrogate such equipment.

Abstract: The uncertainty inherent in high-resolution acoustic pulse-echo distance measuring systems which depend on threshold detection is overcome by transmitting a multi-cycle shot of acoustic energy having a sharply peaked amplitude profile, and locating the peak amplitude of a received echo. The peaked amplitude is achieved by timing the duration of energization of a transducer producing the shot so that energization is terminated before the amplitude of oscillation of the transducer has reached a maximum. This produces a shot which has a definite largest cycle, which should in turn produce an echo having a definite largest cycle.

Abstract: In an acoustic ranging system, an echo signal received following a shot is repeatedly sampled and the samples digitized to produce a statistical data base representing the received echo profile which can be analyzed by various methods to determine the point on the time axis of the profile which corresponds to a wanted echo, and the degree of confidence with which the wanted echo has been identified. The number of shots taken depends upon the conditions at the site being monitored and upon the degree of confidence with which the wanted echo has been determined, and the order in which points in a multipoint system are monitored is determined by an adaptive scanning system which directs shots to different points following a system determined by a predetermined hierarchy, by the results provided by previous shots, by the conditions existing at different points, and by the receipt of outside signals.

Abstract: A tuned acoustic directional transducer for transmitting and receiving airborne sound, which provides enhanced efficiency and reduced cost without undue narrowing of bandwidth, makes use of an acoustic transducer element (2) coupled to a plate (10) having a higher order flexural mode resonance at approximately the desired frequency of operation, the plate being coupled to the air through low-hysteresis acoustic propagation material having an acoustic impedance much less than that of the plate and much greater than that of the air. The material is disposed so that in the desired direction of propagation there is no substantial reduction of sound intensity in the far field resulting from cancellation occasioned by interaction of sound radiated from adjacent antinodal zones. Preferably the thickness of the material is such that it acts as an efficient acoustic impedance matching transformer.