Histograms are used to interpret a time-domain signal in a Tektronix 3000 Series Oscilloscope.
Hi and welcome to our 54th Test and Measurement video. Right now we’ll look at histograms in the amazing Tektronix MDO3104 oscilloscope.
The word histogram has not so much to do with history, although that has been suggested, as with the ancient Greek word histos, meaning the representation of figures that are longer in vertical dimension than in horizontal dimension, like cornstalks in a field. Histograms may be drawn to represent numerical data pertaining to a very broad range of human activities and natural phenomena. Consequently, definitions of the histogram are numerous and diverse. Generally, it resembles a bar diagram that consists of rectangles whose area (and therefore height) is proportional to the number of occurrences of a specified variable and whose width is equal to the interval as defined. The height is naturally greater than the width unless the histogram is intentionally rotated 90 degrees.
In the Tektronix MDO 3000 Series oscilloscope, it is a simple matter to display a histogram. First, display the signal of interest. It can be an external signal connected to a selected analog input channel via probe or BNC cable, or it can be internal, namely the AFG, a Math waveform or a Reference waveform. For this demonstration, we’ve connected the internal arbitrary function generator to the Channel One analog input. Pressing AFG, the default Sine Wave is displayed, but we’ll push the Waveform soft key and using Multipurpose Knob a, scroll down to Noise.
To proceed, press Measure. One of the menu choices that appears below the display is Waveform Histograms. Pressing the associated soft key, the relevant menu appears to the right of the display. The default status for Histograms is Off. Using the soft key, Histograms can be turned On and simultaneously turned to either Vertical or Horizontal. Noise is a very good signal to use for demonstrating how the Histogram works. Amplitude is represented along the Y-axis since we are currently in the time domain. Notice that the trace is brightest near the X-axis, where amplitude is least. This is reflected in the histogram, where length corresponds to frequency, not necessarily in a herzian sense, but corresponding to number of events per unit of time.
Returning to the top menu item on the right side of the display and toggling to Horizontal, we see that all bars are the same length and also there are no spaces between them. This corresponds to the fact that the noise trace is the same average brightness at every point along any line that may be drawn parallel to the X-axis.
Let’s choose some other waveforms and see what the histograms look like. Notice when we cycle through the AFG waveforms, the histogram remains in the display, but it does not change for specific waveforms unless it is refreshed, which is done by cycling the top soft key on the right.
Pressing Measure restores the Measurement Menu so that Waveform Histograms appears, and when it is pressed, the Histogram Menu is restored. The second item, Source, is self-evident. Notice that Math and Reference Waveforms can be accessed and removed. Here is a Reference Waveform, shown in white, and here is a Math waveform, shown in red.
In the Histogram Menu, Horizontal Limits and Vertical Limits can be accessed and adjusted, using Multipurpose Knobs a and b, as indicated by the rectangle in the display. Moreover, DVM can be accessed. As you can see, with Noise at the input, Frequency is all over the place. I hope this video has been useful in demonstrating what histograms are all about. New videos are added periodically, so check back frequently.
Clive says
I have a 25kHz train of 10nsec wide pulses and the amplitude of each pulse varies slightly. Can I use the histogram function to measure the mean and standard deviation of the pulse amplitudes?