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Fault Detection (Sound and Vibration Measurement Suite)»Table of Contents

Sound and Vibration Measurement Suite 6.0 HelpDecember 2007

NI Part Number:372416A-01

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This book discusses how to use the envelope detection technique to perform fault detection on rotating machinery.

Envelope Detection

Envelope detection is a technique to extract the modulating signal, or envelope signal, from an amplitude-modulated signal. You can use the envelope detection technique to identify mechanical faults that have an amplitude-modulating effect on the vibration signal of a machine. The power spectrum of the envelope signal exhibits peaks that can reveal the source of faults.

A fault on a rolling-element bearing or gear tooth typically has an amplitude-modulating effect on the vibration signal of the bearing or gear. You thus can use the envelope detection technique to perform fault detection on rolling-element bearings or gears.

Measuring a Vibration Signal for Envelope Detection

You can use an accelerometer and a tachometer to measure the vibration signal and the rotational speed, respectively, of a rolling-element bearing or gear. Choose a sampling rate that is at least 2.56 times higher than the highest frequency component of the signal of interest. Also choose an accelerometer with a high cutoff frequency to cover the frequency band that the envelope detection technique uses. Then place the accelerometer close to the bearing or gearbox so the distance between the fault location and the accelerometer does not affect the signal transmission. When the accelerometer is far away from the fault location, the envelope detection technique might fail.

Extracting an Envelope Signal

A fault on a rolling-element bearing or gear tooth generates a low-level impulse every time the local fault contacts another part of the bearing or gear. This low-level impulse has an amplitude-modulating effect on the vibration signal. The modulating effect spreads over a wide frequency range because the impulse has a short period. In the low frequency band of the vibration signal, imbalance, misalignment, or mechanical looseness of the bearing or gear might generate vibration signals that overwhelm the low-level impulses. Thus the envelope detection technique focuses on a narrow band range in the high frequency band, which is useful for detecting the low-level impulses that are below the noise level in the normal spectrum. The envelope detection technique involves the following three steps: shifting the narrow band range in the high frequency band to the base band, filtering the frequency-shifted signal using a lowpass filter, and calculating the envelope signal of the lowpass-filtered signal.

You can use the OAT Envelope Detection VI to perform envelope detection on a rolling-element bearing or gear when the rotational speed is constant or when the rotational speed varies. You then can use the SVFA Power Spectrum VI or the OAT Order Power Spectrum VI to display the power spectrum of the resulting envelope signal.

Resources

Sound and Vibration Measurement Suite Shipping Examples- Developer Zone - NI Developer Zone

10 Questions to Ask When Selecting Your Sound and Vibration Measurement System- Developer Zone - NI Developer Zone

Sound and Vibration Functions: Scaling- Developer Zone - NI Developer Zone

 

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You are here:  NI Home  >  Support  >  Product Reference  >  Manuals  > Sound and Vibrat ion Measurement Sui te 6.0 Help

OAT Envelope Detection (Sound and Vibration Measurement Suite)

»Table of ContentsSound and Vibration Measurement Suite 6.0 HelpDecember 2007

NI Part Number:372416A-01

»View Product Info

Extracts the modulating signal, or envelope signal, from an amplitude-modulated signal. You can use the envelope detection technique to identify the mechanical faults that have amplitude-modulating effect on the vibration signal of a machine.

You must manually select the polymorphic instance you want to use.

Examples

Use the pull-down menu to select an instance of this VI.

       

OAT Envelope Detection (Waveform Output, 1 Channel)

reset? specifies the initialization of the internal states. If reset? is TRUE, or when the VI first runs, the internal states initialize to zero. If reset? is FALSE, this VI sets the internal states to the final states from the previous call to the VI. The default is FALSE.

scaled signal [EU] specifies the scaled signal expressed in the selected engineering units. To obtain a properly scaled signal, you can use the SVL Scale Voltage to EU VI or define a virtual channel in Measurement & Automation Explorer (MAX).

band specification specifies the frequency band to use to calculate the envelope signal of

the scaled signal [EU].center frequency [Hz] specifies the center frequency of the frequency band to use to calculate the envelope signal. The default is 4800.

span [Hz] specifies the frequency bandwidth to calculate the envelope signal. The span [Hz] value only defines half of the frequency band, which is from the center frequency [Hz] to the frequency band upper limit. The default is 2000.

error in describes error conditions that occur before this VI or function 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. This VI or function runs normally only if no error occurred before this VI or function runs. 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.status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE.

code is the error or warning code. The default is 0. If status is TRUE, code is a nonzero error code. Ifstatus is FALSE, code is 0 or a warning code.

source specifies the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.

envelope signal [EU] returns the envelope signal of the scaled signal [EU].

error out contains error information. If error in indicates that an error occurred before this VI or function ran,error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out front panel indicator

and select Explain Error from the shortcut menu for more information about the error.

status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred.

code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE,code is 0 or a warning code.

source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning.

OAT Envelope Detection (Waveform Output, N Channels)

reset? specifies the initialization of the internal states. If reset? is TRUE, or when the VI first runs, the internal states initialize to zero. If reset? is FALSE, this VI sets the internal states to the final states from the previous call to the VI. The default is FALSE.

scaled signals [EU] specifies the scaled signals expressed in the selected engineering units. To obtain a properly scaled signal, you can use the SVL Scale Voltage to EU VI or define a virtual channel in Measurement & Automation Explorer (MAX).

band specification specifies the frequency band to use to calculate the envelope signals of

the scaled signals [EU].center frequency [Hz] specifies the center frequency of the frequency band to use to calculate the envelope signal. The default is 4800.

span [Hz] specifies the frequency bandwidth to calculate the envelope signal. The span [Hz] value only defines half of the frequency band, which is from

the center frequency [Hz] to the frequency band upper limit. The default is 2000.

error in describes error conditions that occur before this VI or function 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. This VI or function runs normally only if no error occurred before this VI or function runs. 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.status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE.

code is the error or warning code. The default is 0. If status is TRUE, code is a nonzero error code. Ifstatus is FALSE, code is 0 or a warning code.

source specifies the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.

envelope signals [EU] returns the envelope signals of the scaled signals [EU].

error out contains error information. If error in indicates that an error occurred before this VI or function ran,error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out front panel indicator

and select Explain Error from the shortcut menu for more information about the error.

status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred.

code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE,code is 0 or a warning code.

source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning.

OAT Envelope Detection (Even Angle Output, 1 Channel)

reset? specifies the initialization of the internal states. If reset? is TRUE, or when the VI first runs, the internal states initialize to zero. If reset? is FALSE, this VI sets the internal states to the final states from the previous call to the VI. The default is FALSE.

scaled signal [EU] specifies the scaled signal expressed in the selected engineering units. To obtain a properly scaled signal, you can use the SVL Scale Voltage to EU VI or define a virtual channel in Measurement & Automation Explorer (MAX).

speed profile specifies the arrival time and the rotational speed of each tachometer pulse.time [s] specifies the arrival time, in seconds, of each tachometer pulse.

speed [RPM] specifies the rotational speed, in revolutions per minute, of each tachometer pulse.

pulse/revolution specifies the number of pulses the tachometer generates during each revolution. The default is 1.

band specification specifies the order band to use to calculate the envelope signal of

the scaled signal [EU].center specifies the center frequency or the center order of the order band to use to calculate the envelope signal. Use center frequency for a variable-speed bearing

fault detection.value specifies the value of the center frequency or center order to use to calculate the envelope signal. The default is 0.

unit specifies the unit of the center input. When unit is Hz, value specifies the value of the center frequency. When unit is order, value specifies the value of the center order. 

0 Hz (Default)

1 order

span [order] specifies the order bandwidth to calculate the envelope signal. span [order] value only defines half of the order band, which is from the center to the order band upper limit. The default is 0.

error in describes error conditions that occur before this VI or function 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. This VI or function runs normally only if no error occurred before this VI or function runs. 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.status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE.

code is the error or warning code. The default is 0. If status is TRUE, code is a nonzero error code. Ifstatus is FALSE, code is 0 or a warning code.

source specifies the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.

even-angle envelope signal returns the even-angle envelope signal of the scaled signal

[EU]. even-angle envelope signal is synchronous to the rotational speed with constant number of samples per revolution.

r0 returns the starting index value for counting revolutions.

dr returns the revolution interval between two sequential samples.

Y returns the value of the even-angle-spaced sample in scaled engineering unit.

even-angle channel info returns information about the measurement configuration for the even-angle envelope signal.

error out contains error information. If error in indicates that an error occurred before this VI or function ran,error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out front panel indicator

and select Explain Error from the shortcut menu for more information about the error.

status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred.

code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE,code is 0 or a warning code.

source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning.

actual max order returns the actual maximum order this VI uses.

OAT Envelope Detection (Even Angle Output, N Channels)

reset? specifies the initialization of the internal states. If reset? is TRUE, or when the VI first runs, the internal states initialize to zero. If reset? is FALSE, this VI sets the internal states to the final states from the previous call to the VI. The default is FALSE.

scaled signals [EU] specifies the scaled signals expressed in the selected engineering units. To obtain a properly scaled signal, you can use the SVL Scale Voltage to EU VI or define a virtual channel in Measurement & Automation Explorer (MAX).

speed profile specifies the arrival time and the rotational speed of each tachometer pulse.time [s] specifies the arrival time, in seconds, of each tachometer pulse.

speed [RPM] specifies the rotational speed, in revolutions per minute, of each tachometer pulse.

pulse/revolution specifies the number of pulses the tachometer generates during each revolution. The default is 1.

band specification specifies the order band to use to calculate the envelope signals of

the scaled signals [EU].center specifies the center frequency or the center order of the order band to use to calculate the envelope signals of the scaled signals [EU]. Use center frequency

for a variable-speed bearing fault detection.value specifies the value of the center frequency or center order to use to calculate the envelope signal. The default is 0.

unit specifies the unit of the center input. When unit is Hz, value specifies the value of the center frequency. When unit is order, value specifies the value of the center order. 

0 Hz (Default)

1 order

span [order] specifies the order bandwidth to calculate the envelope signal. span [order] value only defines half of the order band, which is from the center to the order band upper limit. The default is 0.

error in describes error conditions that occur before this VI or function 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. This VI or function runs normally only if no error occurred before this VI or function runs. 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.status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE.

code is the error or warning code. The default is 0. If status is TRUE, code is a nonzero error code. Ifstatus is FALSE, code is 0 or a warning code.

source specifies the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.

even-angle envelope signals returns the even-angle envelope signals of the scaled

signals [EU]. even-angle envelope signals is synchronous to the rotational speed with constant number of samples per revolution.

r0 returns the starting index value for counting revolutions.

dr returns the revolution interval between two sequential samples.

Y returns the value of the even-angle-spaced sample in scaled engineering unit.

even-angle channel info returns information about the measurement configuration for the even-angle envelope signals.

error out contains error information. If error in indicates that an error occurred before this VI or function ran,error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out front panel indicator

and select Explain Error from the shortcut menu for more information about the error.

status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred.

code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE,code is 0 or a warning code.

source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning.

actual max order returns the actual maximum order this VI uses.

Examples

Refer to the following VIs for examples of using the OAT Envelope Detection VI:

Envelope Detection Constant Speed (Offline) VI: labview\examples\Order Analysis\Fault Analysis

Envelope Detection Variable Speed (Offline) VI: labview\examples\Order Analysis\Fault Analysis

Resources

Sound and Vibration Measurement Suite Shipping Examples- Developer Zone - NI Developer Zone

10 Questions to Ask When Selecting Your Sound and Vibration Measurement System- Developer Zone - NI Developer Zone

Sound and Vibration Functions: Scaling- Developer Zone - NI Developer Zone

 

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Products Modular Instruments o Dynamic Signal Acquisition Dynamic Signal Acquisition Devices DSA Software Sound and Vibration Toolkit Sound and Vibration Measurement Suite

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Averaged Frequency Response (DAQmx)1 ratings | 1.00 out of 5

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This VI generates and acquires data for an averaged frequency response measurement. This VI performs a continuous acquisition and stops when the averaged measurement is complete. You specify the initial settling time of the device under test and the averaging parameters to use for the frequency response measurement. The graph outputs display the acquired stimulus and response signals versus time and the magnitude and phase of the frequency response versus frequency. This program is a shipping example VI included with the NI Sound and Vibration Measurement Suite and NI Sound and Vibration Toolkit. 

This Virtual Instrument is designed to work with data acquisition hardware from National Instruments. To find compatible hardware for this application, visit ni.com/soundandvibration. 

This software is written in LabVIEW, a graphical programming language designed for scientists and engineers. For more information about LabVIEW, visit ni.com/labview. 

Sound and Vibration Developers Library The NI Sound and Vibration Developers Library is your one-stop online resource for learning about and downloading code for acoustic analysis, machine diagnostics and audio test functions. On this page, you will find links to detailed tutorials, application notes, example programs, and analysis function descriptions.

More information on National Instruments signal processing can be found at the Signal Processing Resource Center.

Downloads

Filename: sv_avg_freq_response.viRequirements: View

Front Panel

This is a picture of the VI's front panel. To view the block diagram and additional documentation, download the attached file.

This example requires LabVIEW and the Sound and Vibration Measurement Suite.  If you do not have access to these, you can always try them out online at the LabVIEW Online Evaluation.

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Visit the NI Sound and Vibration Portal Compare Sound and Vibration Software Signal Processing Resource Center Test-Drive NI Sound and Vibration Analysis Software Online Learn more about NI LabVIEW

Requirements

Filename: sv_avg_freq_response.viSoftware Requirements

Application Software: LabVIEW Full Development System 8.2 Toolkits and Add-Ons: LabVIEW Sound and Vibration Toolkit 5.0 

Hardware Requirements

Hardware Group: CompactDAQ, Dynamic Signal Analyzers (DSA), Multifunction DAQ (MIO)Driver: NI-DAQmx 8.3 

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LegalThis example program (this "program") was developed by a National Instruments ("NI") Applications Engineer. Although technical support of this program may be made available by National Instruments, this program may not be completely tested and verified, and NI does not guarantee its quality in any way or that NI will continue to support this program with each new revision of related products and drivers. THIS EXAMPLE PROGRAM IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND AND SUBJECT TO CERTAIN RESTRICTIONS AS MORE SPECIFICALLY SET FORTH IN NI.COM'S TERMS OF USE (http://ni.com/legal/termsofuse/unitedstates/us/).

 

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