An ultrasonic level or sensing system requires no contact with the target.For many processes in the medical,pharmaceutical,military and general industries this is an advantage over inline sensors that may contaminate the liquids inside a vessel or tube or that may be clogged by the product.
Both continuous wave and pulsed systems are used.The principle behind a pulsed-ultrasonic technology is that the transmit signal consists of short bursts of ultrasonic energy.After each burst,the electronics looks for a return signal within a small window of time corresponding to the time it takes for the energy to pass through the vessel.Only a signal received during this window will qualify for additional signal processing.
A popular consumer application of ultrasonic ranging was the Polaroid SX-70 camera which included a light-weight transducer system to focus the camera automatically.Polaroid later licenced this ultrasound technology and it became the basis of a variety of ultrasonic products.
Motion sensors and flow measurement
A common ultrasound application is an automatic door opener,where an ultrasonic sensor detects a person's approach and opens the door.Ultrasonic sensors are also used to detect intruders; the ultrasound can cover a wide area from a single point.The flow in pipes or open channels can be measured by ultrasonic flowmeters,which measure the average velocity of flowing liquid.In rheology,an acoustic rheometer relies on the principle of ultrasound.In fluid mechanics,fluid flow can be measured using an ultrasonic flow meter.
Ultrasonic testing is a type of nondestructive testing commonly used to find flaws in materials and to measure the thickness of objects.Frequencies of 2 to 10 MHz are common but for special purposes other frequencies are used.Inspection may be manual or automated and is an essential part of modern manufacturing processes.Most metals can be inspected as well as plastics and aerospace composites.Lower frequency ultrasound (50–500 kHz) can also be used to inspect less dense materials such as wood,concrete and cement.
Ultrasound inspection of welded joints has been an alternative to radiography for non-destructive testing since the 1960s.Ultrasonic inspection eliminates the use of ionizing radiation,with safety and cost benefits.Ultrasound can also provide additional information such as the depth of flaws in a welded joint.Ultrasonic inspection has progressed from manual methods to computerized systems that automate much of the process.An ultrasonic test of a joint can identify the existence of flaws,measure their size,and identify their location.Not all welded materials are equally amenable to ultrasonic inspection; some materials have a large grain size that produces a high level of background noise in measurements.
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