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Standard measurements
In the cursor window of each graph and in meters, various different measurements can be selected. These measurements include:
| Icon | Measurement |
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Maximum |
 |
Minimum |
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Top-Bottom |
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RMS |
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Mean |
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Variance |
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Standard Deviation |
 |
Frequency |
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Crest factor |
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Rise time |
 |
Fall time |
 |
dBm |
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Total Harmonic Distortion (THD) |
In the cursor window the following additional measurements are possible:
| Icon | Measurement |
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Left |
 |
Right |
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Right-Left |
Short description
This section gives a short description of the standard measurements. Most measurements are very straight forward, but are explained for clarity.
The measurements are calculated over a sample range. When using the cursor window, the sample range is equal the samples in between the left and right cursor. In a meter object, the sample range is equal to the post samples.
Some measurements are explained with a formula. In these formulas the following applies:
- m corresponds to the index of the first sample in the sample range
- n corresponds to the index of the last sample in the sample range
- N is the number of samples in the sample range and is equal to n - m + 1
- xi corresponds to the ith sample
Maximum
The measurement maximum is the highest value in the sample range.
Minimum
The measurement minimum is the lowest value in the sample range.
Top-Botttom
The measurement top-botttom, also known as peak-peak is the highest value in the sample range minus the lowest value.
Root Mean Square (RMS)
The measurement RMS is equal to the square root of the mean of the square of all samples in the sample range. This is a whole mouth full and a formula is clearer:
Mean
The measurement mean is the mean value of all samples in the sample range.
Variance
The measurement variance is a measure of how values are distributed around the mean value.
Standard Deviation
The measurement standard deviation (σ) is equal to the square root of the variance. The standard deviation is equal to the RMS value for signals with a zero mean value (AC signals).
Frequency
The measurement frequency determines the frequency of a time based signal. The frequency is determined by searching the rising slopes in a signal and measuring the time between them.
For a correct measurement, at least two rising slopes must be present in the sample range.
Crest factor
The Crest factor is equal to the peak amplitude of a waveform divided by the RMS value.
The Crest factor can be used to get an idea of the quality of a signal. A signal with more peaks will have a higher Crest factor. The following table lists some Crest factors for some ideal standard signals.
| Signal type | Crest factor |
| Sine | √2 ≈ 1.414 |
| Triangle | √3 ≈ 1.732 |
| Block | 1 |
| DC | 1 |
Rise time
The rise time is the time it takes for the signal to rise from 10% to 90% of its top-bottom value. The first slope in the sample range is used.
Fall time
The fall time is the time it takes for the signal to fall from 90% to 10% of its top-bottom value. The first slope in the sample range is used.
dBm
dBm is the power ratio in decibels of the measured power referenced to one milliwatt. The following formula is used, in which a reference resistor Rref of 600Ω is used to convert the measured voltage to power.
Total Harmonic Distortion (THD)
The THD measurement can be used on frequency based signals or spectra. It is a measure of the distortion in a signal and is equal to the power in the higher harmonics divided by the power in the base frequency of a signal. In the formula below, Vi is magnitude of the ith harmonic of a the signal.
Left
The measurement left can be used in the cursor window. It is the value of the signal at the position of the left cursor.
Right
The measurement right can be used in the cursor window. It is the value of the signal at the position of the right side cursor.
Right-Left
The measurement right-left can be used in the cursor window. It is the difference between the magnitude of the signal at the position of the right and left cursor.