How does the detection range of ultrasonic sensors work? Ultrasonic sensors are able to perform a reliable detection or measurement within a certain area without contact on the basis of ultrasonic sound waves. The frequency and amplitude with which these are sent out determine, among other things, the range of the sensor. This allows one ultrasonic sensor to be used in a level measurement at a water tank where a larger measuring range is required than with conventional ultrasonic sensors with a smaller or medium range.
In addition, the surface of the transducer (transmitter, integrated in the sensor head) partly determines with which power the sound wave can be sent (and received) and thus partly determines the range. Ultrasonic sensors with a longer range therefore have a larger sensor head, such as the crm+600/DIU/TC/E.
A few important specifications can be distinguished within the detection range of ultrasonic sensors. Firstly, the operating detection range: the range within which the sensor must be able to perform a detection or measurement at all times, regardless of the shape or size of the object. Secondly, the limit detection range, in other words the maximum range that the sensor can achieve. Thirdly, there is the so-called blind zone.
Types of detection ranges: operating detection range and limit detection range
The operating detection range
The operating detection range and limit detection range of an ultrasonic sensor are defined based on two standard measurements. Firstly, the sensor is tested on a thin beam of steel (10×27 mm). These are relatively complex objects to detect for an ultrasonic sensor, because of the round shape of the object and the fact that the majority of the echo is deflected in all directions. With this testing method the operating detection range is defined. Roughly it can be said that, next to color- and material-independence, the detection is in a sense also insensitive to the shape of the object.
This is an essential characteristic for a sensor that is used in an application such as a level measurement of bulk goods. You can think of iron ores in a chute with the same color. The ultrasonic sensor will perform a level measurement with ease and within the set measuring range.
The limit detection range
Other than the operating detection range, a limit detection range is also specified. The limit detection range, which is specified as the regular detection range by almost every other manufacturer, is the maximum range that can be reached by an ultrasonic sensor. Large objects, that are detected easily, are used to determine the limit detection range of an ultrasonic For this, a flat plate (approx. 500×500 mm) is used as an object that can be considered as easily detectable. As a rule of thumb, the limit detection range of the sensor is 25 to 50% larger than the operating detection range. The limit detection range is viewed as the maximum reachable distance. Herein it is important to take environmental conditions into consideration, because the limit detection range is only utilized optimally when all conditions are very good to optimal.
Outside the detection range: the blind zone
The blind zone is the first area seen by the sensor, starting from the sensor head. In this area, the sensor can perform no reliable measurements. The size of the blind zone of a sensor is dependent on physics. Firstly, it depends on the frequency with which the sound wave is sent out and this in turn relies on the run-time of sound. The combination of these two factors makes it impossible to perform a reliable measurement in the first area in front of the sensor. As a rule of thumb one can say that the blind zone is roughly in between 5 – 10% of the maximum measuring range of the sensor.