Experiment: Elevator

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Elevator
Experiment Elevator
Category Everyday life
Used sensors Pressure


The experiment "Elevator" determines the speed of an elevator by tracking the changes in atmospheric pressure. It shows the distance, velocity and acceleration (the latter one from the accelerometer).

Example of an elevator over 5 floors.

Requirements

There are no requirements, but the results tend to be nicer if the elevator covers at least three floors.


Setup

There is no specific setup. Just enter an elevator and start the experiment


Analysis

The pressure sensor is extremely precise and designed to determine the user's vertical position. phyphox will take the first reading from this sensor as zero elevation and use the barometric formula to subsequently derive changes in height. As it does only need relative changes, no reference pressure is used, but an average value at sea level ("international barometric height formula"), which is sufficient to determine relative changes at ground level (absolute heights are more problematic).

The speed of the elevator is just the first derivative of the height data over time.

Problems and resolutions

  • There is a significant rise/fall in the data just at the beginning of the experiment while the elevator is not even moving. This happens for many pressure sensors when turning them on at a different atmospheric pressure then the last time they were in use. Often, the change in atmospheric pressure due to the weather is enough for this to happen, if you have not used this sensor for a few hours. Some sensors may show some delay befor giving first data to cover up this effect, but it may still be visible. However, you can simply stop the experiment, clear the data and start over as it should not happen the second time. If you want to be sure that your measurement succeeds on the first try (for example if you had to wait in line for a special elevator or a theme park ride), just start and stop the experiment once before starting the actual measurement to avoid this effect.


Demonstration video