Effects of Sample Rate and Number of Points on Noisy Signal Characterization

Physics 240

The following plots represent data that were taken using a National Instruments USB-6221-BNC analog i/o board. The signal was the voltage across a 1N4148 diode when driven by a constant 100 μA current. The voltage is temperature dependent but the diode was maintained at room temperature with some slow variations.

There were two sets of data taken. In the first the number of samples and the sample rate were varied to maintain an acquisition duration of 0.1 s. The number of samples followed a 1-2-5 sequence from 2 to 10,000 samples.

The second set was taken by using the same sequence of number of samples but the data were taken at sample rates of 1 kHz, 10 kHz, and 100 kHz for each.

There are two plots for each case. The first shows the actual data acquired. The caption includes the conditions (number of samples and sample rate) as well as the mean value for the data and the standard deviation for that data (σS). The number in parentheses floowing the standard deviation is the estimate of the standard deviation in the value of the mean given by σS/N1/2. The second shows a histogram of the data overlaid by a Gaussian calculated from the value of the mean and the standard deviation. The bins were chosen to be separated by the code width of the USB-6221-BNC operated at a gain of ±1 V with the centers at the values returned from the board.

The Plots