Question

Explain the principle of operation of an ultrasonic sensor for use in an industrial automation application. Answer should include details on the type of target that can be detected, effect on sensing distance of different target types, typical sensing distance and what the term ‘blind zone’ refers to in relation to these sensors.

Answer 1

Ultrasonic sensor: the name itself suggest that it is a sensor which depends on sound waves which have frequencies we humans can't hear. ultrasonic sensor works on the principle of echoes.

ultrasonic sensors uses transducers and transmits the frequency signals greater than 20KHz(sound waves). when the frequency signal hits the target and reflect back to the sensor in the form of echoes, the sensor detects the signal using a microphone. when the signal is detected it analyses the time lapse between the transmitted and received ultrasonic pulses to calculate the distance.

Now when a target is solid, it reflects 90% of the ultrasonic pulses back to the sensor. But when the targets like wool are selected which doesn't have higher density of atoms in a unit area, it absorbs the incident ultrasonic sound. As a result the sensor wont be able to determine the distance to the target.

So Ultrasonic waves are used to enable stable detection of transparent objects, solids and some types of liquids which have higher density of atoms in it.

therefore, when solids are the targets, the distance calculated is closely accurate.

the factors which effect the sensing distance are:

1.external Noise.

2.atomic density of the target.

3.Size, shape, and the orientation of the target.

Now, Dead zone or blind zone refers to the are of an ultrasonic sensor at which the sensor can't make measurements or can give readings which are false. when the ultrasonic sensor is supplied a voltage to produce pulses, the sensor vibrates continuously. As a result of this energy will be released and this energy release will have to dissipate before the echo is returned from the target. if not dissipated then, the dead zone occurs and occupies the area upto which the energy is being dissipated.

due to this reason, we have to ensure that the target is outside of dead zone of ultrasonic sensor.

this dead zone expansion will mainly depend upon the frequency of excitation. since higher frequency would cause the ringing phenomenon(vibration) in the sensor to increase.

Finally, the maximum distance upto which the sensor can calculate without missing accuracy is called as typical sensing distance.

Hope this helps.

Do give a like if you like the answer. it'll encourage me to write more quality answers.