Amplitude Measurements (Cycle Average and RMS) (G Dataflow)

Version:

Returns the average and RMS levels of a specific cycle of a periodic signal.

signal

The input signal.

This input can be a waveform or an array of waveforms.

Each waveform is required to contain at least a specific number of complete cycles defined by cycle number, where a cycle is defined as the interval between two consecutive rising middle reference level crossings.

cycle number

Cycle, or period, of the periodic signal on which to perform the measurement.

reference levels settings

High, middle, and low reference levels of a waveform.

high ref level

High reference level of the waveform.

After the signal crosses the mid ref level in the rising direction, it must cross the high ref level before the next falling mid ref level crossing can be counted.

Default: 90

mid ref level

Middle reference level of the waveform.

The interval between consecutive rising mid ref level crossings defines one cycle, or period, of the waveform. At least one high or low reference level crossing must separate each mid ref level crossing.

Default: 50

low ref level

Low reference level of the waveform.

After the signal crosses the mid ref level in the falling direction, it must cross the low ref level before the next rising mid ref level crossing can be counted.

Default: 10

ref units

Units of the high, middle, and low reference levels.

Name Value Description
absolute 0 Interprets the reference levels as absolute levels.
percent 1 Interprets the reference levels as a percentage of the full range of the waveform.

Default: percent

error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

state levels settings

Settings that determine the high and low state levels of a waveform.

method

Method this node uses to compute the high and low state levels of the waveform.

Name Description
histogram Returns the levels of the histogram bins with the maximum number of hits in the upper and lower regions of the waveform. The upper and lower regions of the waveform include the upper and lower 40%, respectively, of the peak-to-peak range of the waveform.
peak Searches the entire waveform for its maximum and minimum levels.
auto select Determines whether the histogram bins that correspond to the high and low state levels each have over 5% of the total hits. If so, this node returns those results. Otherwise, this node uses the peak method. This ensures a reasonable answer for either a square wave (ignoring the overshoot and undershoot) or a triangle wave (where a histogram fails).

Default: auto select

histogram size

Number of bins in the histogram this node uses to determine the high and low state levels of the waveform.

If you select the peak method, this node ignores this input.

Default: 256

histogram method

Method this node uses to compute the histogram. Currently, mode is the only available histogram method.

Name Description
mode Uses the mode method.

reserved

Value reserved for future use.

cycle average

Mean level of one complete period of a periodic input waveform.

This output can return a double-precision, floating-point number or a 1D array of double-precision, floating-point numbers.

Algorithm for Calculating cycle average

The following equation computes the cycle average:

$\text{average}=\frac{1}{\text{numPoints}}\underset{i=\text{cycle}}{\sum }\text{waveform}\left[i\right]$

where i indicates the waveform samples that fall in the single period specified by cycle number and numPoints is given by the following equation:

$\text{numPoints}=\mathrm{int}\left(\frac{\text{period}}{dt}+0.5\right)$

where dt is the time between two samples and int() is a function that returns the integer portion of a floating-point number.

The cycle average of a perfect sine wave is zero, while the average level of the entire waveform can be nonzero due to partial periods at the boundaries of the waveform.

cycle RMS

Root mean square value of one complete period of a periodic input waveform.

This output can return a double-precision, floating-point number or a 1D array of double-precision, floating-point numbers.

Algorithm for Calculating cycle RMS

The following equation computes the RMS value:

${\text{RMS}}_{\text{cycle}}=\sqrt{\frac{1}{\text{numPoints}}\underset{i=\text{cycle}}{\sum }{\left(\text{waveform}\left[i\right]\right)}^{2}}$

where i indicates the waveform samples that fall in the single period specific by cycle number and numPoints is given by the following equation:

$\text{numPoints}=\mathrm{int}\left(\frac{\text{period}}{dt}+0.5\right)$

where dt is the time between two points and int() is a function that returns the integer portion of a floating-point number.

error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

measurement info

Measurement cycle interval end points and the absolute reference levels used to define the measurement cycle.

This output can return a cluster or a 1D array of clusters.

start time

Time of the rising middle reference level crossing that defines the start of the measurement interval.

end time

Time of the rising middle reference level crossing that defines the end of the measurement interval

ref levels

Three user-defined reference levels of the waveform in absolute units.

high ref level

The high reference level.

mid ref level

The middle reference level.

low ref level

The low reference level.

ref units

Units of the reference levels.

ref units is always absolute in measurement info.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

Web Server: Not supported in VIs that run in a web application