Standard measurements

In the cursor window of each graph and in meters, various different measurements can be selected. These measurements include:

In the cursor window the following additional measurements are possible:

Short description

This section gives a short description of the standard measurements for the meter and cursors.

The measurements are calculated over a sample range. When using the cursor window with the vertical cursors switched on, the sample range is equal to the samples in between the left and right cursor. When the vertical cursors are switched off, or 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

MaximumMaximum

The measurement Maximum is the highest value in the sample range.

MinimumMinimum

The measurement Minimum is the lowest value in the sample range.

Maximum-MinimumMaximum-Minimum

The measurement Maximum-Minimum, also known as peak-peak is the highest value in the sample range minus the lowest value.

Root Mean Square (RMS)Root Mean Square (RMS)

The measurement RMS is equal to the square root of the mean of the squares of all samples in the sample range:

RMS formula

MeanMean

The measurement Mean is the mean value of all samples in the sample range.

Mean formula

VarianceVariance

The measurement Variance is a measure of how values are distributed around the mean value.

Variance formula

Standard DeviationStandard 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).

Standard Deviation formula

FrequencyFrequency

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.

PeriodPeriod

The measurement Period determines the period time of a time based signal. The period time 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.

Duty cycleDuty cycle

The measurement Duty cycle is defined as the ratio between the time that a signal is higher than half the amplitude and the period. It is expressed as a percentage.

Duty cycle invertedDuty cycle inverted

The measurement Duty cycle inverted is defined as the ratio between the time that a signal is lower than half the amplitude and the period. It is expressed as a percentage.

Crest factorCrest factor

The Crest factor is equal to the peak amplitude of a waveform divided by the RMS value.

Crest factor formula

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 typeCrest factor
Sine √2 ≈ 1.414
Triangle √3 ≈ 1.732
Block 1
DC 1

Rise timeRise 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 rising slope in the sample range is used.

Fall timeFall 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 falling slope in the sample range is used.

Slew rateSlew rate

The Slew rate is defined as the change of voltage per unit of time and is expressed in V/s. The first edge in the sample range is used.

dBmdBm

dBm is the power ratio in decibels of the measured power referenced to one milliwatt. The following formula is used, in which an adjustable virtual reference resistor Rref is used to convert the measured voltage to power. The default value of Rref is 600Ω

dBm formula

PowerPower

Power shows the amount of electrical power that is dissipated in a virtual reference resistor by the measured signal. The following formula is used, in which an adjustable virtual reference resistor Rref is used to convert the measured voltage to power. The default value of Rref is 600Ω

Power formula

Period countPeriod count

Period count determines the number of periods in a signal. It uses the mid level crossings in the signal to determine the amount of periods.

For a correct measurement, at least three mid level crossings must be present in the sample range.

Pulse countPulse count

Pulse count determines the number of rising pulses in a signal. It uses the mid level crossings in the signal to determine the amount of pulses.

For a correct measurement, at least two mid level crossings must be present in the sample range.

Pulse count negativePulse count negative

Pulse count negative determines the number of falling pulses in a signal. It uses the mid level crossings in the signal to determine the amount of pulses.

For a correct measurement, at least two mid level crossings must be present in the sample range.

Edge Count RisingEdge Count Rising

Rising edge count determines the number of rising edges in a signal. It uses the mid level crossings in the signal to determine the amount of edges.

For a correct measurement, at least two mid level crossings must be present in the sample range.

Edge Count FallingEdge Count Falling

Falling edge count determines the number of falling edges in a signal. It uses the mid level crossings in the signal to determine the amount of edges.

For a correct measurement, at least two mid level crossings must be present in the sample range.

Total Harmonic Distortion (THD)Total Harmonic Distortion (THD)

The Total Harmonic Distortion (THD) is defined as the ratio between the power of the harmonic frequencies above the base frequency and the power of the base frequency. This ratio is displayed in dB. It is a measure of the distortion in a signal.

The THD is calculated using the following formula:

THD formula

where V1 is the RMS amplitude of the base frequency and V2 to Vn are the RMS amplitudes of each higher harmonic.

The THD measurement can only be used on frequency based signals or spectra.

LeftLeft

The measurement Left can be used in the cursor window. It is the value of the signal at the position of the left cursor.

RightRight

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-LeftRight-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.

SlopeSlope

The Slope of a signal is the change of magnitude divided by the elapsed time. The measurement slope determines the slope in a signal between the left and the right cursor.

Slope formula

TopTop

The measurement Top can be used in the cursor window. It represents the value of the signal at the position of the top cursor.

BottomBottom

The measurement Bottom can be used in the cursor window. It represents the value of the signal at the position of the bottom cursor.

Top-BottomTop-Bottom

The measurement Top-Bottom can be used in the cursor window. It represents the difference between the signal magnitudes at the positions of the top and bottom cursor.

Reference resistor

A user configurable virtual impedance is available that is used by the Power measurement Power and the dBm measurement dBm. Cicking the impedance Impedance button in the cursor readout window will allow to set its value. Its default value is 600 Ohm.