Abstract: A coin-operated vending machine accepts any combination of valid coins which are deposited and automatically returns the correct change when the merchandise is dispensed. The amount of change represents the difference between the total value of the accepted coins and the price of the selected merchandise. A digital data processing circuit is employed for recognizing the validity and denomination of all deposited coins and any unacceptable coin that falls outside the established tolerance limits for a genuine valid coin is automatically rejected and immediately returned.

Abstract: A microphone is described for operating in dirty environments where a layer of dirt or mud may accumulate over the vibratile surface of microphone. The microphone is designed with its vibratile diaphragm having a mass greater than 0.4 gm/sq cm of diaphragm area so that an added layer of dirt over its surface will not cause any significant change in the sensitivity of the microphone over its prescribed frequency range of operation.

Abstract: A molded rubber tubular member includes a grommet-like flange at its open end for permitting the structure to be attached to a panel. A recessed nest portion is provided at the opposite end of the tubular member into which is inserted a transducer whose diaphragm serves as a closure at the end of the tubular member. The assembly serves as a flexible shock mount for the transducer and also as an acoustic amplifier which increases the acoustic sensitivity of the transducer by 10 to 20 dB in a selective frequency band within the audible range.

Abstract: A comprehensive analysis of the effect of air turbulence on the acoustic performance of an ultrasonic intruder alarm system indicates that air turbulence does not cause Doppler frequency shifts in the received signal in the frequency region 2 - 100 Hz, as has been universally assumed in prior art systems but that air turbulence can only produce amplitude modulations in the received signal over this frequency region. It is also disclosed that changes in air velocity, or accelerations of the air flow, cause only very low Doppler frequency shifts in the signal, below 2 Hz for a 20 kHz carrier, and only moving targets can produce higher Doppler frequency shifts. A processing system is disclosed which is immune to false alarms in the presence of air turbulence without sacrificing threshold sensitivity and without introducing long time delays in the signal processing circuit as has been necessary in prior art systems.

Abstract: This invention provides an expendable velocimeter probe. High frequency transmitting and receiving transducers are mounted opposite to one another in axial alignment on the probe body and on a frame in front of the body. The mounting includes means for accurately adjusting the distance between the transducers in order to provide low cost, but highly reliable, means for calibrating the velocimeter during large scale manufacture of the instruments.