ULTRASONIC

Principle
Basic mode of operation
Ultrasonic sensors operate in reflex mode. An ultrasonic transducer emits and receives the ultrasonic signala. Within a stipulated distance range, the incoming echo is checked, the time taken for the sound to travel the distance is determined and a corresponding output signal is emitted. If the distance between the sensor and the objects is too small, the echo arrives before the ultrasonic transducer has reached steady state and is ready to receive. Objects in this dead band cannot be detected reliably.

Objects may be moved towards the ultrasonic sensor either frontally or from the side. If it has a smooth surface, the object must enter the sensor's range perpendicular to the sensor axis. If its position deviates from this axis, the object must be brought nearer. Response curves of the sensorSU-D2000-M30N-C1-POSA : level target, 700 x 700 mmB : level target, 100 x 100 mmC : felt tube, f 16 mmD : round bar smooth, f 25 mm
This results in a so called sound cone as a function of response distance to angle. The minimum size of the object also determines its nature and surface. This means that different sound cones result for different objects and, sensors with a longer range require larger objects.

Deflection and beaming One special aspect of the ultrasonic technique is the capability of deflecting sound with smooth reflector. This allows the level of an aggressive fluid to be measured for instance. By contrast, measuring errors occur if the sound is to be beamed or deflected with smooth tubes for instance.

Mutual interaction Neighbouring ultrasonic sensors influence each others mutually, and the extend of this influence can generally be determinated only experimentally. The synchronisation input with which the measurement operation can be disabled alternately offers one advantageous solution. The disable times must be selected depending on the times taken for the sound to travel the distance.