
Jade 1.0 Technical NoteAccuracy of ReadingsJade Capture records the noise levels by converting the voltage received from the meter into a corresponding decibel level. The accuracy of the data read from a sound level meter during data capture is therefore heavily reliant on the accuracy of the hardware and the care taken by the user. The following list contains those things that will affect the accuracy of data capture:
Single versus dual level calibrationJade Capture uses the results of the software calibration to determine the mapping of the voltage levels output by the meter to decibel levels. Figure 1 shows the possible difference in accuracy of single and dual level software calibration.
The purpose of a software calibration is to calculate the voltage level for the bottom of range or 0dB (BOR in Figure 1). To find this value, Jade Capture calculates the slope of the line that plots the mapping of voltages to decibel levels. From the diagram it can be seen that if two calibration levels (C1 and C2) are known, calculating the slope of the line is easy. This is shown by the solid sloping line. Once the slope is known, Jade Capture can calculate the "milliVolts per dB" value and enter the correct value in the meter library for use during data capture. If there is no second calibration level, Jade Capture extrapolates the line backwards from the first calibration level (C1 in Figure 1) using the "milliVolts per dB" value entered by the user in the meter library. The effect of doing this is shown by the dotted line in the diagram. As you can see from the diagram, the final slope from both types of calibration may be considerably different. For example, in Figure 1, if a voltage level (V) is read from the meter, the single level calibration results in the decibel level shown by D1 and the dual level calibration results in the decibel level shown by D2. In this example, the dB value is too low if the results of the single level calibration are used. If you have only a single level calibratorIf you have only a single level calibrator, you should do one of the following:
Note that neither of these alternatives will be as accurate as a proper dual level calibration, so you should obtain a dual level calibrator at the first opportunity. Copyright © Ptolemy Services 1997 