Ultrasonic Sensing/Control Basics
Ultrasonic signals are like audible sound waves, except the frequencies are much higher. Our ultrasonic transducers have piezoelectric crystals which resonate to a desired frequency and convert electric energy into acoustic energy and vice versa. The illustration below shows how sound waves are reflected from a target back to the transducer. An output signal is produced to perform some kind of indicating or control function. A minimum distance from the sensor is required to provide a time delay so that the "echoes" can be interpreted. Variables which can affect the operation of ultrasonic sensing include: target surface angle, reflective surface roughness or changes in temperature or humidity. The targets can have any kind of reflective form - even round objects.
Advantages of Ultrasonic Sensors
When used for sensing functions, the ultrasonic method has unique advantages over conventional sensors:
- Discrete distances to moving objects can be detected and measured.
- Less affected by target materials and surfaces, and not affected by color.
- Can detect small objects over long operating distances.
- Resistance to external disturbances such as vibration, infrared radiation, ambient noise,    and EMI radiation.
Two Ultrasonic Sensor Types
The following diagrams summarize the distinctions between proximity and ranging ultrasonic sensors:
1) Proximity Detection
An object passing anywhere within the preset range will be detected and generate an output signal. The detect point is independent of target size, material, or degree of reflectivity.
2) Ranging Measurement
Precise distance(s) of an object moving to and from the sensor are measured via time intervals between transmitted and reflected bursts of ultrasonic sound. The example shows a target detected at six inches from sensor and moving to 10 inches. The distance change is continuously calculated and outputted.
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