Smartphones as ammeters
With the help of this experiment the magnetic sensor of the smartphone can be used as an ammeter (from Ampere Meter) for direct current.
Requirements and experimental material
- smartphone (with phyphox-app and magnetic sensors)
- a coil (more windings for finer readings)
Since the magnetic field induced in a coil by direct current is proportional to the current of the circuit, one can use this to indirectly measure amperage with the magnetic sensor of smartphone.
Hence a coil of small diameter (in this example a custom wound coil of coated copper wire) is placed near the magnetic sensor of the smartphone. The .phyphox-file linked at the bottom allows the smartphone to convert the measured magnetic field into amperage after calibration.
As the relation of amperage and magnetic field of a coil are proportional to one another, a calibration via two data pairs of current and magnetic field is sufficient. Figure 1 shows the "Calibration"-page of the .phyphox-experiment. On this page the currently measured magnetic field is displayed and the two data pairs can be inserted.
After calibrating the setup, the "display"-page can be opened. Here the measured current is displayed in number- as well as graph-form, this page is shown in figure 2.
Troubleshooting and Tipps
- One of the two data pairs needed for calibration can be acquired via measuring without current.
- The position of the coil is key: Moving the coil destroys the calibration. It is therefore recommended to fix the coil to the smartphone or mark the position of it.
- Moving the smartphone can also destroy the calibration since the influence of the earth's magnetic field can change.
- More accurate measurements can be acchieved by using coils with more windings, or inserting an iron core into the coil (the latter is of course only viable when measuring magnetic fields low enough to neglect the hystersis effect).