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DHARMENDRA KUMAR MISHRA

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INTRODUCTION
Ultrasonic sensors (also known as transceivers when they both send and receive) work on a principle similar to radar or sonar which evaluate attributes of a target by interpreting the echoes from radio or sound waves respectively
What is Sensor or Transducer
• An ultrasonic transducer is a device that converts energy into ultrasound, or sound waves above the normal range of human hearing.
Construction
• Ultrasonic Level Sensor is consist of two main parts .
• Transmitter
• Receiver
WORKING
This sensor provides very fast and reliable data output. Whole answer is mainly dependent upon time delay or lag. The ultrasonic sound is created by the Piezoelectric crystal inside the sensor. It converts electrical energy to ultrasonic sound energy.
Advantages
1. Non disturbing technique.
2. Can be used for wide range of things like solid and liquids with wide range of viscosity.
3. Low price.
4. High functionality.
5. Very accurate and low error.
6. Long life instrument.
7. Can measure the level of different liquids having different densities in same tank
Limitations
• 1. Sensor mounting must be properly done.
• 2. Tank should be free from obstacles otherwise it may cause error in measurement.
• 3. Result may get affected due to change in temperature or pressure inside the tank or container
Applications
• Automatic pump control.
• Flow measurement.
• open channel flow measurement.
• Used in water/waste applications.

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Ultrasonic sensors are based on the measurement of the properties of sound waves with a frequency higher than the human audible range. They are based on three physical principles: flight time, Doppler effect and attenuation of sound waves. Ultrasonic sensors are not intrusive because they do not require physical contact with their target, and they can detect certain bright or bright targets, otherwise obscured by some vision-based sensors. On the other hand, its measurements are very sensitive to the temperature and the angle of the objective.

Ultrasonic sensors are "based on measuring the properties of acoustic waves with frequencies above the human audible range", often at approximately 40 kHz 1). They usually operate by generating a high-frequency sound pulse, and then receive and evaluate the properties of the echo pulse.
Three different properties of the received echo pulse can be evaluated for different detection purposes. They are:
 Flight time (for detection distance)
 Doppler shift (to detect speed)
 Amplitude attenuation (to measure distance, directionality or attenuation coefficient).



Performing measurements

The three above methods make use of different physical principles, but all of them use the same measurement procedure. In each case, an ultrasonic sound wave is created, received and evaluated.

Ultrasonic signal generation

Ultrasound is most commonly generated as a direct conversion of electrical energy. This is achieved by applying an electrical rapid-swing signal to a piezoelectric crystal attached to a mounting. The charge causes the crystal to expand and contract with the voltage, thus generating an acoustic wave. The waves are later detected by a piezoelectric receiver, which converts the waves back into voltage using the same method.
The signal can also be generated by consumer electronic products, but great care must be taken to ensure that the signal does not dim in this range. The speakers typically have filter circuits to prevent ultrasonic propagation, and the frequency response of many microphones rolls off in this range. This is due in part to the amount of ultrasound present in our daily lives; Percussive sounds and metallic timbre contain ultrasonic frequencies.

Considerations

The main advantage of ultrasonic sensors is that measurements can be made without touching or otherwise preventing the lens. Also, depending on the measured distance, the measurement is relatively fast (it takes approximately 6 ms for the sound to travel 1m). However, many factors such as temperature, angle and material can affect measurements.

Here is a list of pitfalls in ultrasonic detection:
 Time. Temperature and humidity affect the speed of sound in the air. Therefore, scope meters may need to be recalibrated for accurate measurements in a new environment. (O, an on-board temperature sensor can be incorporated).
 Currents. Variations in temperature and air currents can create invisible boundaries that reflect ultrasonic waves, so care must be taken to avoid them.
 Angle. For the transmitted wave to return the echo to the receiver, the target surface must be perpendicular to the transmitter. Therefore, round objects are more easily detected, as they always show some perpendicular faces. When orienting a flat object, care must be taken to ensure that its angle to the sensor does not exceed a particular range.
 Dead zone. Ultrasonic sensors often have a "dead zone" immediately in front of them, where objects can not be detected because they divert the wave backward before the receiver is operational. (This is because reverberations of the transmitter force the receiver to pause for a moment before beginning to hear the echo)
 Material. Some materials are more absorbent than others, and these will reflect less ultrasound. This complicates the use of the attenuation method to measure the distance of arbitrary objects.