Ultrasonic Presence Sensors with Wide Range and High Local Resolution
Valentin Mágori, H. E. Walker · IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control · 1987
Ultrasonic presence sensors based on the impulse-echo method are being used in industrial automation for detecting the pres- ence of objects (e.g., workpieces) and for monitoring their position. By defining time windows, i.e., time intervals with respect to the instant of emission of the ultrasound, one or more distance intervals can be pre- set as selected detection ranges, within which the sensor responds. The logical combination of different time windows can be used for improv- ing the significance of the sensor output, for distinguishing between objects of different size, for monitoring the direction of their motion, etc. A selected detection range is laterally confined by the high direc- tivity of the ultrasonic transducers used. These are planar piezocer- amic devices of special design with a rugged quarter-wave matching layer. They are made for different frequencies in the range of 26-400 kHz and have low insertion losses (36 dB) and a small radiation ange of 5, formed by an aperture of 12-15 wavelengths. With a 200-kHz transducer of our RU-series, a presence sensor for the range of 0.2- 1 m, divided into eight detection ranges, has been developed and suc- cessfully applied in industrial automation. Recent developments com- prise a modular system of presence sensors with different operating frequencies, achieving different ranges: 80 kHz for 0.8-6 m, 200 kHz for 0.2-1 m and 400 kHz for 6-30 cm. Time windows with variable width can also monitor the actual distance to an object. The adjustable sensing bead, which can also be mounted separately, provides addi- tional flexibility.