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

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.

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?

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
NI 4461	Yes	-120 dB	3.4 Hz	Differential/Pseudodifferential
NI-4462	Yes	-120 dB	3.4 Hz	Differential/Pseudodifferential
NI 4496	Yes	-114 dB	0.5 Hz	Pseudodifferential
NI 4498	Yes	-114 dB	0.5 Hz	Pseudodifferential
NI 4472	Yes	-110 dB	0.5 Hz	Pseudodifferential
NI 4474	Yes	-110 dB	3.4 Hz	Pseudodifferential
NI 9233	Yes	-102 dB	0.5 Hz	Differential
SCXI-153x	Yes	-50 dB	0.2 Hz	Differential/Single-Ended
SCC-ACC01	Yes	-60 dB	0.8 Hz	Differential/Single-Ended

See Also:
NI 4461 data sheet  
NI 4462 data sheet
NI 4496 data sheet
NI 4498 data sheet  
NI 4472 data sheet
NI 4474 data sheet  
NI 9233 data sheet

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

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, as prescribed by the Nyquist sampling theorem. Below is a table of the NI devices and their maximum frequency ranges.

Product	NI 4461	NI 4462	NI 4496	NI 4498	NI 4472	NI 4474	NI 9233	SCXI-153x	SCC-ACC01
Maximum Frequency Range	95 kHz	95 kHz	95 kHz	95 kHz	47 kHz	47 kHz	20 kHz	20 kHz	5 kHz

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 4496*	NI 4498*	NI 4472	NI 4474	NI 9233	SCXI-153x	SCC-ACC01
Dynamic Range	116 dB	118 dB	113 dB	113 dB	110 dB	110 dB	90 dB	80 dB	80 dB
Input Range	+/-316 mV to +/-42.4 V	+/-316 mV to +/-42.4 V	+/-1 V to +/-10 V	+/-316 mV to +/-10 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.

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 4461	Yes	Yes		2
NI 4462	Yes	Yes		4
NI 4496	Yes			16
NI 4498	Yes			16
NI 4472	Yes	Yes		8
NI 4474		Yes		4
NI 9233			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
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

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 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 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 9233	Yes	Yes -- Up to 32 channels
SCXI-153x	Yes	Yes
SCC-ACC01	No

See Also:
PXI information

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

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:

[+] Enlarge Image

9. Do you need a portable measurement system?

NI provides three solutions that are portable for most applications. The first configuration uses the New  CompactDAQ module NI-9233 with CompactDAQ chassis with USB connection to laptop. The second 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-9233, NI-9172 cDAQ Chassis, Laptop, LabVIEW, Sound and Vibration Toolkit

  

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

  

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

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. Visit ni.com/products for the price of each product.

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 Analysis
More Information on Sound and Vibration Measurement and Analysis Products

Reader Comments | Submit a comment »

document should be updated with latest information
The document contains references to a PCI-6052E board which should be replaced with a reference to an M-Series board. The document contains also benchmark information about a PXI-8176 controller. This information should be updated with benchmarks for the latest PXI-controllers (PXI-8196)
- Jan 18, 2006

You listen to your customers
The width, depth and detail given in this overview make it easy for me to search in the right direction. I appreciate this kind of information a lot.
- d.troester@computer.org - Apr 17, 2003