Answered: UltraSonic Sensor's Hysteresis

In the old Vex Forums I saw a statement declaring that there is hysteresis in the distance measurements the Ultrasonic Sensor will report.

I am perplexed why this is true (what is the manufacturer’s motivation for doing it). And, if the hysteresis can’t be turned off, I suppose I am “eager” to know the details about how the sensor’s output characteristics are affected by it.

Before reading that statement in the old forums I would have assumed that any time I pointed the sensor at any reflective object that wasn’t too close or too far away, and then pinged; I would get a reasonably accurate measurement of the current distance to that object, and that I would never get some value left over from a previous “ping”.

What info can you give us to help us understand the hysteresis in the sensor’s outputs?


We have removed the pervious post about hysteresis. We believe the previous post was not accurate. Hysteresis can not be turned off. There is hysteresis in the amplitude detection of the sensor, but its impact on distance measurement should be negligible. You should get a reasonably accurate measurement of the distance to an object, and will not get some value left over from a previous “ping”. You may see some variation due to the angle of the response depending on background texture, the reflecting surface, size, distance, etc. You may also see variations depending on how you write your code for the sensor.

OK - Thanks RT,


So was the other user’s experience perhaps due to a moderately fat beamwidth detecting the wall that was not perpinducular to the sensor, but was still close enough to perpindicular (and rough enough) to create a detectable return?

Are you able to publish some specs on the beam patterns for us?


It would be hard to say what was happening without more details on the setup and what they were doing with the data from the sensor.

Unfortunately, we do not have any beam pattern data to publish.