ARMS Acoustic Radiometer Measurement System
- ARMS Data and Plots:
- The ARMS collects data automatically, at the rate of 4 seconds per measurement. After the data have been gathered, the ARMS program will plot the data and display statistics on the data. The first example shows data from a transducer that was emitting about 50 mW of ultrasound power. There were 20 measurements made, so the whole measurement set took 80 seconds to complete. The first plot shows the measurements. The second plot shows the averaged measurements, with each point on the plot indicating the mean of all the measurements made up to that point. The third display shows statistics calculated from the data.
- The second example shows data collected with no ultrasound present This set of measurements took about 33 minutes to complete.
- By averaging measurements, the vibration-induced "noise" in the measurement can be reduced. As more measurements are averaged, the effect of noise on the mean measurement is reduced. The reduction in noise is inversely proportional to the square root of the number of measurements. The values listed above in the statistics printout labeled "Standard Deviation of the Mean" is an estimate of the tolerance we can put on the measurements, based on the standard deviation, or "noise level" present in the measurement set. Up to 10,000 measurements may be averaged in a measurement set, reducing noise by a factor of 100.
