Cursor readouts show the time or amplitude of the waveform at the cursor location as shown in Figure 3. Improving the accuracy of cursor measurementsĬursors are vertical and/or horizontal lines that can be moved over the oscilloscope or digitizer display to mark significant points on a waveform. The signal is clearly discernible after either type of signal processing. Both averaging and filtering reduce the noise and improve the dynamic range of the measurement. In the bottom trace, a Gaussian low pass filter has been applied to the acquired signal. The center trace shows the average of multiple acquisitions. Note that the signal disappears into the noise about three quarters of the way across the screen. The acquired signal is an exponentially damped sine wave. Figure 2 shows the improvement that can be achieved using either averaging or filtering.įigure 2 Averaging multiple acquisitions or filtering a single acquisition can improve the dynamic range of the acquisition by eliminating noise. This assumes that the signal has a low bandwidth and is not affected by the bandwidth reduction. Reduce the bandwidth by a factor of four to achieve a two-to-one improvement in dynamic range. The improvement of dynamic range is proportional to the square root of the bandwidth reduction. It does require multiple acquisitions.įor a single acquisition, you can reduce noise by bandwidth limiting the signal. This can bring a low level signal out of background noise for better measurements. Ensemble averaging, where the n th samples of each acquisition are averaged together over multiple acquisitions, reduces Gaussian noise proportional to the square root of the number of averaged signals. Use signal processing in the form of averaging or filtering to reduce noise, improve dynamic range and measurement accuracy. Improve dynamic range and measurement accuracy by eliminating noise If you don’t have access to a multiple grid oscilloscope, make sure that any measurements are made on the full amplitude signals, reserve the attenuated signal for visual comparisons only. This is not a problem for an oscilloscope or digitizer that has multiple grid displays, each grid displays the signal at full dynamic range and multiple signals can be compared, each in its own grid. Measurements made on the attenuated trace will have increased uncertainty due to a poorer signal-to-noise ratio. If you vertically expand the attenuated trace and display it at the original 50mV/division, the vertical noise has increased significantly as you can tell from the thickening of the displayed trace. The top trace shows the trace acquired at one quarter of the full screen or 200mV/division. The bottom grid shows the original signal acquired a 50mV/division. Figure 1 An example of the decrease in signal-to-noise ratio due to reducing the signal amplitude in order to fit multiple traces on a single grid.
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