# Ultrasonic beam width problem

Hi guys,

I am currently attempting to measure the length of objects by using an ultrasonic radar. As the Radar sweeps left to right the program saves the angle and distance of detection and then saves the angle and distance on losing the object, this gives me 2 distances and an angle i can use to find the length of the opposite.

This would give me the entire length of the opposite were the echo was received not the length of the object. So i thought if i take the beam width away (The data sheet says the beam is 15 degrees) from this x2 for the beam just touching the object either side it would give me the length of the object, however i have carried out a few experiment with the HC-SRo4 and the results i am getting are not accurate.

Am i missing something with regards to how the beam changes? Or does anyone have an idea how i can overcome this problem. Please help :o

Cheers :o

Do not cross post!

pylon:
Do not cross post!

Duplicate deleted.

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Am i missing something with regards to how the beam changes?

Possibly, or you made a mistake.

up874227:
Hi guys,

I am currently attempting to measure the length of objects by using an ultrasonic radar. As the Radar sweeps left to right the program saves the angle and distance of detection and then saves the angle and distance on losing the object, this gives me 2 distances and an angle i can use to find the length of the opposite.

This would give me the entire length of the opposite were the echo was received not the length of the object. So i thought if i take the beam width away (The data sheet says the beam is 15 degrees) from this x2 for the beam just touching the object either side it would give me the length of the object, however i have carried out a few experiment with the HC-SRo4 and the results i am getting are not accurate.

Am i missing something with regards to how the beam changes? Or does anyone have an idea how i can overcome this problem. Please help :o

Cheers :o

What you are missing is the definition of "beam width". The sound outside of the 15 degree beam does not just disappear. The beam width means the strength of the sound is reduced by some value and may be less than the receiver can use. And it may not be the same from sensor to sensor. This may be something you will have to measure for your particular sensor.

Paul