Calculating the width of an ultrasonic beam can be a little tricky at times, but we’ve done it enough (for over 20 years) that we can give you a solid reference point. However, we have to make a key assumption in order to do it – maximum sensitivity settings.
If you have your sensitivity turned all the way up on your ultrasonic sensor, then the beam expands 9° off center for about 12 to 15 ft., after which it narrows again. So for the first 12 to 15 ft., we can determine your beam width, or spread, with reliability.
How do I calculate the beam spread?
The typical ultrasonic sensor beam spread at maximum sensitivity is 38 inches across at 10 ft. away from the sensor’s face.
To calculate the beam spread at maximum sensitivity use the following formulas:
Distance in Feet X 3.8 (constant) = Beam Spread (inches)
Example: 10 ft. X 3.8 = 38 inches
Distance in Inches X .317 (constant) = Beam Spread (inches)
Example: 120 inches X .317 = 38 inches
Keep in mind that maximum sensor sensitivity is usually not needed to obtain the best reading. If you’d like to figure this out, give us a call and we can help. However, the fastest method to get things working right in the field is to adjust your sensor settings until an optimal reading is achieved.
APG ultrasonic sensors have an Auto Sense mode, which optimizes readings automatically in most applications. If manual adjustment is needed, contact us and we’ll guide you through it.
Why does It matter?
Beam spread becomes really important when trying to send the signal between physical obstructions. For example, many tanks and wells have pipes, ladders, or other equipment attached to the walls. If an ultrasonic beam hits the obstacle, it will return a signal back to the sensor and give a false reading.
Why does the beam retract after 12 to 15 ft.?
Like the ripples in water, sound waves only carry so much energy, which is focused in the center. After 12 to 15 ft., depending on your model, the outer reaches of the sound wave become too weak to return to the sensor. While there is still a sound wave traveling at 9° from it’s origin, it will never make it back to the sensor.
This effectively narrows the beam spread once the apex is reached. Again, the specifics all depend on the model and the settings of your ultrasonic sensor.