10 Questions to Ask When Selecting Your Sound and Vibration Measurement System

Publish Date: Jan 07, 2013 | 31 Ratings | 4.16 out of 5 |  PDF

Overview

Sound and vibration analysis plays a major role in many different applications areas such as – audio, noise, vibration, and harshness (NVH) , machine monitoring, structural dynamics, and sound quality. Each of these application areas differs in engineering task (product design, production test, machine performance, or process control) and has a different set of concerns (sensors, frequency range, sampling rates, cost, etc). The following document will focus on the different concerns that need to be considered when selecting a sound and vibration measurement system.

Table of Contents

  1. 1. Which sensor(s) are you using?
  2. 2. What signal conditioning is needed?
  3. 3. What is your frequency range of interest?
  4. 4. What is the required dynamic range?
  5. 5. How many analog input and output channels do you need?
  6. 6. Do you need phase information (simultaneous sampling)?
  7. 7. Which measurements do you need?
  8. 8. What hardware platforms are available?
  9. 9. Do you need a portable measurement system?
  10. 10. How much does it cost -- that is, do you need real-time or gap-free processing or streaming to disk?

1. 1. Which sensor(s) are you using?

The type of sensor you choose depends on which signal you are measuring. For sound and vibration applications, common signals are acceleration, displacement, and sound pressure level. Common sensors to measure these parameters are accelerometers, proximity probes, and microphones, respectively. You should first know the type of sensor you intend to use, because this largely governs your choice of hardware. Some of the questions that your choice of sensor places on the hardware are as follows:
· What kind of signal conditioning is required?
· What is the frequency range of the sensor?
· How much dynamic range does the sensor require?

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2. 2. What signal conditioning is needed?

Before it is digitized by the data acquisition hardware, the signal from a sensor nearly always requires some type of conditioning, such as amplification, filtering, sensor excitation, and input configuration. NI has many hardware products that have built-in excitation for voltage mode or Integrated Electronic Piezoelectric (IEPE) microphones and accelerometers. Below is a table that contains the specific values for the various signal conditioning options that are provided on each NI product.

Product
IEPE
Alias Rejection
AC Coupling
Input Configuration
Yes
-101 dB
0.8 Hz
Pseudodifferential
Yes
-101 dB
0.8 Hz
Pseudodifferential
Yes
-120 dB
3.4 Hz
Differential/Pseudodifferential

NI 4462

Yes

-120 dB

3.4 Hz
Differential/Pseudodifferential

NI 4495

No

-114 dB

DC Coupled

Pseudodifferential

NI 4496

Yes

-114 dB

0.5 Hz

Pseudodifferential

NI 4498

Yes

-114 dB

0.5 Hz

Pseudodifferential
Yes
-110 dB
0.5 Hz
Pseudodifferential
Yes
-110 dB
3.4 Hz
Pseudodifferential

NI 9233

Yes(always on)

-102 dB

0.5 Hz

Pseudodifferential

NI 9234

Yes

-102 dB

0.5 Hz

Pseudodifferential
Yes
-50 dB
0.2 Hz
Differential/Single-Ended
Yes
-60 dB
0.8 Hz
Differential/Single-Ended

See Also:
NI 4431 data sheet
NI 4432 data sheet
NI 4461 data sheet  
NI 4462 data sheet
NI 4495 data sheet
NI 4496 data sheet
NI 4498 data sheet  
NI 4472 data sheet
NI 4474 data sheet  
NI 9233 data sheet
NI 9234 data sheet

SCXI-1530 data sheet
SCXI-1531 data sheet
SCC-ACC01 data sheet

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3. 3. What is your frequency range of interest?

All sensors have a frequency range over which they are designed to operate. Your sensor should have a frequency range large enough to cover the frequency range of interest. Likewise your digitizing hardware should have a large enough frequency range to cover the signals of interest. To prevent aliasing, NI products come with antialiasing filters, which cut the maximum frequency range of the device to a little less than one-half the maximum sampling rate. Below is a table of the NI devices and their maximum frequency ranges.

Product
NI 443x
NI 4461
NI 4462
NI 4495
NI 4496
NI 4498
Maximum Frequency Range
47 kHz
95 kHz
95 kHz
95 kHz
95 kHz
95 kHz

 

Product
NI 4472
NI 4474
NI 923x
SCXI- 153x
SCC- ACC01
Maximum Frequency Range
47 kHz
47 kHz
21 kHz
20 kHz
5 kHz

 

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4. 4. What is the required dynamic range?

Dynamic range is a measure of how small you can measure a signal relative to the maximum input signal the device can measure. Expressed in decibels, the dynamic range is 20 log (Vmax/Vmin). For example, the NI 4472 has an input range of ±10 V and a dynamic range greater than 110 dB, for example a voltage ratio of 106. Thus, with a maximum signal of 10 V, the smallest signal that you can see on the NI 4472 is 10 µV. Thus, the input range and the specified dynamic range are important for determining the needs of your system. Below is a table of NI devices, their input ranges, and dynamic ranges.

Product
NI 4461*
NI 4462*
NI 4495*
NI 4496*
NI 4498*
NI 4431
Dynamic Range (dB)
116
118
114
113
113
101
Input Range
+/-316 mV to+/-42.4 V
+/-316 mV to
+/-42.4 V
+/-1 V to
+/-10 V
+/-1 V to
+/-10 V
+/-316 mV to +/-10 V
+/-10 V

 

Product
NI 4432
NI 4472
NI 4474
NI 923x
SCXI -153x
SCC- ACC01
Dynamic Range (dB)
101
110
110
102
80
80
Input Range
+/-40 V
+/-10 V
+/-10 V
+/-5 V
+/-24 V
+/-5 V

*These products have various gains that you can apply to the signal to effectively increase the dynamic range.

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5. 5. How many analog input and output channels do you need?

Sound and vibration applications require various numbers of analog inputs and outputs depending on the application. With tools from NI, you can expand your system to the number of channels of your choice by simply adding more devices. For instance, using the NI 4472, with its eight input channels, you can fill an 18-slot PXI chassis with seven modules and achieve 112 analog input channels. In addition, you can synchronize multiple-chassis up to 5,000 channels. The tables below show the number of channels each NI device offers.

Product
Platform
Analog Input Channels

 

PXI
PCI
USB

 

NI 4431

 

 

Yes

4

NI 4432

 

 

Yes

5

NI 4461
Yes

Yes

 

2

NI 4462

Yes

Yes

 

4

NI 4495

Yes

 

 

16

NI 4496

Yes

 

 

16

NI 4498

Yes

 

 

16

NI 4472
Yes
Yes

 

8
NI 4474

 

Yes

 

4

NI 923x

   

Yes

4

*It is recommended that you use no more than three devices in a standard desktop computer because of heating and cooling issues. You can use more than three devices in an industrial computer where proper cooling and power requirements are met.

Product
Platform
Analog Output Channels

 

PXI
PCI
USB

 

NI 4431

 
 
Yes

1

NI 4461

Yes
Yes
 

2

NI 5411

Yes
Yes
 

1

NI 5401

Yes
Yes
 

1

NI 6731

Yes
Yes
 

4

NI 6733

Yes
Yes
 

8

 

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6. 6. Do you need phase information (simultaneous sampling)?

Simultaneous sampling is needed in applications where phase information between measurements of two separate channels is required. Phase information is used in applications that require a frequency response of an object or applications that use cross-channel measurements, such as sound intensity or structural analysis. Simultaneous sampling is available on most NI sound and vibration measurement products.

Furthermore, multiple-device synchronization for phase information across multiple channels is possible with most NI products. The NI 4472 for PXI performs synchronization across multiple modules by using the PXI Star Trigger bus. This guarantees a phase mismatch of less than 0.5 deg across the entire frequency range of the product between any two channels in the same chassis. Using the RTSI bus, you can synchronize the NI 445x devices for PCI. The NI 455x devices have built-in simultaneous sampling between channels on the same device, but cannot be synchronized between devices. You can synchronize the SCXI-153x modules if they are used in parallel with multiple DAQ devices, which are synchronized using the RTSI bus. Two or more SCC-ACC01 modules, with only a single channel per device, cannot be synchronized. The following table describes the NI devices that offer simultaneous sampling and multiple-device synchronization.

Product
Simultaneous Sampling
Multiple-Device Synchronization
NI 443x
Yes
 
NI 4461
Yes
Yes -- 500+ PXI -- Up to 3,000 channels
NI 4462
Yes
Yes -- 5 PC, 500+ PXI -- Up to 3,000 channels
NI 4496
Yes
Yes -- 500+ PXI -- Up to 13,000 channels
NI 4496
Yes
Yes -- 500+ PXI -- Up to 13,000 channels
NI 4498
Yes
Yes -- 500+ PXI -- Up to 13,000 channels
NI 4472
Yes
Yes -- 5 PC, 500+ PXI -- Up to 5,000 channels
NI 4474
Yes
Yes -- 5 PC -- Up to 20 channels
NI 923x
Yes
Yes -- Up to 32 channels
SCXI-153x
Yes
Yes
SCC-ACC01
No
 
See Also:
PXI information

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7. 7. Which measurements do you need?

NI provides a number of software tools for analysis of acquired signals. Your application may require analysis such as power spectrum, octave analysis, or order analysis. LabVIEW provides a number of frequency measurements and analysis tools for various applications. The Sound and Vibration Toolkit and the Sound and Vibration Measurement Suite, which are add-on software packages for LabVIEW, provide application-specific analysis.

To learn more about the toolkits and the functionality contained within each, please visit NI Sound and Vibration Software.

See Also:
LabVIEW information
LabVIEW Sound and Vibration Toolkit data sheet
LabVIEW Order Analysis Toolkit data sheet

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8. 8. What hardware platforms are available?

NI provides a number of platform options from single slot USB sleeves (maximum of 4 channels) to Multi-chassis PXI configuration (maximum of 13,000 channels).  The following graph shows the range of measurement platforms available:

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9. 9. Do you need a portable measurement system?

NI provides four solutions that are portable for most applications. The first configuration uses the NI USB-443x series for easy connection to a laptop. The second configuration uses an NI CompactDAQ module NI-923x with a CompactDAQ chassis with USB connection to laptop. The third configuration is created using a 4-slot PXI chassis filled with NI 4472 or NI 4461 modules. This configuration provides up to a 24-channel portable solution.

Portable Configurations

1.  NI USB-443x, Laptop, LabVIEW, Sound and Vibration Toolkit

   

2.  NI 923x, NI-9172 cDAQ Chassis, Laptop, LabVIEW, Sound and Vibration Toolkit

  

3. NI 4472, PXI-1002, PXI Controller, LabVIEW, Sound and Vibration Toolkit

  

4.  SCC-ACC01, SC-2345, DAQCard AI-16XE-50, laptop, LabVIEW, Sound and Vibration Toolkit
  

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10. 10. How much does it cost -- that is, do you need real-time or gap-free processing or streaming to disk?

This is a very important question in selecting any type of sound and vibration measurement system. We provide tools that you can configure in systems for a fraction of the cost of traditional sound and vibration measurement systems. The cost of your individual system depends on the components you use.
We provide a large number of tools for your sound and vibration measurement system. Your system can be expandable, flexible, and customizable to your application using existing hardware and application software. You can also integrate your system with other measurement devices to configure a complete measurement system.

See Also:
More Information on Sound and Vibration Measurement and Analysis Products

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