This chart rates the performance of various technologies with certain influences.
Often, the question comes up “Should I use a diffuse photoelectric sensor or an ultrasonic sensor?" The following chart dives more deeply into this question.
An ultrasonic sensor consists of:
For operation, the transducer is stressed by high voltage. This causes the transducer to vibrate due to the piezo-electric effect and transmit a sound burst into the air. At this point, the clock-pulse generator switches the sensor to receive mode and time measurement begins. When the sound burst hits the target, an echo is reflected back at the transducer. The echo of the sound burst causes the transducer to vibrate due to the piezo-electric effect and time measurement stops.
Distance to the target is calculated with the time measurement using the equation:
d = c * t / 2
where d = distance (m)
c = speed of sound (m/s)
t = time (s)
The ultrasonic transducer is constructed as shown in this image.
Some ultrasonic sensors rely solely on the echo from a target. These are known as diffuse reflection sensors. The following figure shows the detection zone and output status. Note the blind zone – the minimum distance required for the sensor to generate, receive and evaluate a signal.
Retro-reflective sensors are used for objects with poor sound reflection performance such as foam, ragged surfaces and for angled shapes. There is no blind zone with these sensors; however, a reflector, such as a metal plate or wall is required.
Response curves help the user determine the suitability of a particular ultrasonic sensor to solve a specific application. These curves are shown on the product datasheet and in the “Info Card” available for download from the datasheet and are relevant to targets approaching the sensor laterally.
For targets approaching the sensor axially (as in a tank level application), the sensor will detect the target as soon as it reaches the switch-on curve.
For applications where the sound curve is too large, consider using the E23000 to better focus the sound.
Testing in the specific application may be needed to ensure proper function.
Ultrasonic sensors are not affected by changes in air temperature (they have temperature compensation built in), air pressure and humidity. However, other factors can effect performance.