24 - Measuring the speed of sound in air (Mo�on W ir Int eless erf sensor) ace The Mo�on sensor measures distance by calcula�ng the �me for a pulse of ultrasound to travel to an object and return. We can therefore use it to calculate the speed of sound in air.
What you need V-series wireless logger Mo�on sensor - set first to the Time range then the Distance range Temperature sensor Calculator
What you need to do 1.
Connect the Mo�on sensor and the Temperature sensor to the data logger. Connect the logger to your Bluetooth enabled device.
2.
Select the Devices icon and change the range of the Mo�on sensor to Time.
3.
Click on the chart type icon in the top le� of the graph screen and change it from a graph to a meter display.
4.
Posi�on the Mo�on sensor as shown in the diagram, the distance (d) needs to be at least 1 metre measured from the sensors mesh to the surface. The flat surface needs to be a good reflec�ng surface (something “hard” like a wall or piece of card). Ensure the face of the sensor is ver�cal.
5.
Click start and the Meters display will show a reading of the �me it takes for the pulse to travel to the flat surface and back again (2d). The �me reading will be in microseconds (us). Keep a record of the �me and temperature.
6.
Select stop.
7.
Click on device and change the Mo�on sensors range to Distance (if you have mul�ple distance ranges chose the one closest to the distance being used. Click play and measure the exact (d) in metres.
Results Convert the reading from microseconds to seconds i.e. 1 microsecond = 10-⁶ seconds so divide by 1,000,000 e.g. 5855 μs = 0.005855 seconds. Find the velocity of sound in metres per second. (Remember the pulse has travelled twice the distance recorded).
Extension: The velocity of sound changes with temperature. At 0°C the velocity of sound = 331.3 metres per second. The velocity of sound increases at 0.607 metres per second per degree Celsius. (Ref Kaye and Laby) At 24 °C velocity of sound = (24 x 0.607) + 331.3 = 345.9 metres per second. Compare your results with the standard.
Data Harvest Smart wireless ac�vi�es
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