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Making a measurement (2)

Extrapolation method

This method compensates for drifts by averaging the change in mass at turn on and turn off.

• Measure the temperature of the water
• Take a reading at T = 0 s [M(0)]. Switch on the drive signal to the transducer immediately.
• Take a reading at T = 10 s [M(10)]
• Take a third reading at T = 20 s [M(20)] and switch off the drive signal to the transducer immediately.
• The process can be repeated for the ON-OFF transition taking the reading M(20) as the new initial reading M(0)
• The readings M(10) and M(20) will be used to extrapolate back to M₂(0). Subtract the difference between the two readings and subtract from M(10) to calculate M₂(0).
• The change in mass can be calculated from the difference between M(0) and M₂(0)

Using the standard equation P = cF = cmg and a nominal water temperature of 20°C (c = 1482.36 ms^-1), the results from extrapolation method yield the equivalent acoustic power as 96 mW.