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Owning Palette: Order-Domain Measurements Express VIs

Installed With: Sound and Vibration Measurement Suite

Locates tachometer pulse positions in an analog tachometer signal and calculates the rotational speed for a single channel. This step enables you to condition the tachometer signal by setting the number of pulses per revolution, threshold, hysteresis, slope, and minimum pulse width.

Dialog Box Options

Block Diagram Inputs

Block Diagram Outputs

Dialog Box Options

Parameter	Description
Tachometer signal	Displays the input time waveform that contains the tachometer signal. Autoscale—Automatically adjusts the scales of the graph to display the data.
Speed profile	Displays the rotational speed waveform calculated from the input tachometer signal. Autoscale—Automatically adjusts the scales of the graph to display the data.
Input	Specifies the tachometer signal for which this step computes a speed profile. This option is available only with the NI Sound and Vibration Assistant. Input signal—Specifies the tachometer signal.
Configuration	Specifies the settings for conditioning the input tachometer signal. Contains the following options: Pulse/Revolution—Specifies the number of pulses the tachometer generates during each revolution. The default is 1. Auto threshold—Specifies whether this step automatically sets the Threshold and Hysteresis values for the analog tachometer signal. The default is to automatically set the threshold and hysteresis. Threshold—Specifies the trigger level that a tachometer pulse must cross to be considered valid. Changing the Threshold level also changes the position of the Threshold cursor on the Tachometer signal plot. The default is 2. Hysteresis—Specifies a level above or below the Threshold level. Use Hysteresis to reduce false triggering that noise in an analog tachometer signal might cause. When the Slope is Rising, the analog tachometer signal must fall below Threshold minus Hysteresis before this step detects the next pulse. When the Slope is Falling, the analog tachometer signal must rise above Threshold plus Hysteresis before this step detects the next pulse. A Threshold + Hysteresis or Threshold - Hysteresis cursor is available on the Tachometer signal plot when you enter a value for Hysteresis. Changing the Hysteresis level also changes the position of the Threshold + Hysteresis or Threshold - Hysteresis cursor on the Tachometer signal plot. The default is 0.
Advanced Settings	Contains the following options: Rotation direction—Specifies the direction in which the shaft rotates. CCW—(Default) Counterclockwise. CW—Clockwise. Pulse Definition—Contains the following options: Slope—Specifies the type of edge that indicates the arrival of a tachometer pulse. Rising—(Default) Specifies that a rising edge indicates the arrival of a tachometer pulse. Falling—Specifies that a falling edge indicates the arrival of a tachometer pulse. Min pulse width (samples)—Specifies the minimum number of points a valid tachometer pulse must contain. Min pulse width (samples) must be greater than zero. The default is 2. Speed Profile—Specifies the settings for the output rotational speed waveform. Interval (s)—Specifies the time interval of the output rotational speed waveform. Interval (s) must be greater than zero. The default is 10m.

Block Diagram Inputs

Parameter	Description
analog tacho signal	Specifies the time waveform that contains the analog tachometer signal.
error in	Describes error conditions that occur before this Express VI runs. The default is no error. If an error occurred before this VI or function runs, the VI or function passes the error in value to error out. If an error occurs while this VI or function runs, it runs normally and sets its own error status in error out. Use the Simple Error Handler or General Error Handler VIs to display the description of the error code. Use error in and error out to check errors and to specify execution order by wiring error out from one node to error in of the next node.
reset	Specifies the initialization of the internal state of the VI. The default is FALSE.

Block Diagram Outputs

Parameter	Description
speed profile	Returns the rotational speed waveform that this Express VI calculates from the input tachometer signal.
error out	Contains error information. This output provides standard error out functionality.
no speed detected	Indicates whether the analog tacho signal contains tachometer pulses.
current speed	Returns the last rotational speed measurement, in revolutions per minute.