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Qsources: Acoustic and Structural Exciters

Siemens Experimenter Siemens Experimenter
Siemens Experimenter

 

What is a Qsource?

 

Qsources are excitation devices which enable measuring acoustic and structural transfer functions. Qsources come in two product families: acoustic and structural.

 

Qsource products cover a wide range of typical reciprocal transfer function measurements. The sources are available in a variety of sizes and capacities which mean they can excite a range of products: from electronic components to off-highway equipment.

 

Transfer function measurements require:

  • Dedicated excitation hardware
  • Measurable inputs, ideally with integrated sensors
  • Negligible effect on the system under measurement (negligible mass loading, negligible acoustic impact)
  • Sufficient excitation input levels (especially when exciting full vehicles or large structures)

The Qsource excitation product family meets these requirements.

0.pngQsources can be easily installed and used on virtually any type of structure.

 

Acoustic sources emit measurable acoustic force called Q (often referred to as volume acceleration with units of m3/s2). Read this article for more details: What is the Acoustic Quantity Called Q?

 

Structural excitation sources emit measurable force levels (N). The sources can emit a range of excitation types, including sine, sweep, random, burst random, and much more. 

 

This article will break down the Qsource product catalogue by acoustic and structural Qsources.

 

Index:

1.     Acoustic sources

1.a: Setup of acoustic sources

1.b : Low frequency monopole source (Q-MED)

1.c: Low-mid frequency source (Q-LMF)

1.d: Mid-high frequency source (Q-MHF)

 

2.    Structural sources

2.a: Setup of structural sources

2.b: Thumper shaker (Q-TMP)

2.c: Integral shaker (Q-ISH)

2.d: Miniature shaker (Q-MSH)

2.e: High frequency shaker (Q-HSH)

2.f: Amplifier (Q-AMP)

 

1. Acoustic Qsources

 

Acoustic Qsources are omni-directional sources which emit acoustic force (Q). These sources are used for efficient acquisition of acoustic and vibro-acoustic transfer functions.

 

All of the acoustic sources contain an integrated volume acceleration sensor to directly measure acoustic force Q, without requiring any additional post-processing.  The sensor is time stable and virtually independent of the acoustic field in which it is being used, resulting in accurate input measurement.

 

The Siemens portfolio consists of three acoustic exciters:

  • Low frequency monopole source (Q-MED)
  • Low-mid frequency source (Q-LMF)
  • Mid-high frequency source (Q-MHF)

All of the acoustic sources contain integrated electronic protection units that protect the sources against excessive voltage and current levels.

 

A quick comparison of the source specifications is available in the table below:

 

1.pngFigure 1: Overview of the specifications for each Qsource.

 The frequency ranges and input levels of the acoustic Qsources are visually represented below (Figure 2).

 

2.pngFigure 2: Visual comparison of the frequency and output levels for each acoustic source.

1.a: Setup of the Acoustic Sources:

 

All of the acoustic sources are setup in a similar way:

  1. Connect the PC to the SCADAS. The PC will control the output signal using Simcenter Testlab. The PC will also store the data acquired with the SCADAS.
  2. Connect the output of the SCADAS to a power amplifier.
  3. Connect the output of the power amplifier to the source input.
  4. Connect the source output to the input of the SCADAS system. All of the sources output Q.

 3.pngFigure 3: Schematic of measurement chain for the acoustic Qsources.

See this article for videos on the setup of Qsource Acoustic exciters. In the sections below are more details on each acoustic source (Q-MED, Q-LMF, Q-HMF). 

 

1.b: Low frequency monopole source (Q-MED):

 

4.gifFigure 4: Detail view and specs for the low frequency monopole source.

The low frequency monopole source (Q-MED) allows for measuring vibro-acoustic transfer functions with high output at low frequencies. The source can be used for both direct and reciprocal measurements. The source is omnidirectional, meaning it emits the same acoustic field in all directions (omnidirectional up to 2,000 Hz).

 

The small size (Ø75mm x 200mm) allows for easy positioning. This is especially useful when performing acoustic modal analysis, in which the source needs to be moved several times. 

 

The source is compatible with multiple output types, including pink noise (which emits more energy at low frequency).

 

The Q-MED measures volume displacement directly rather than volume acceleration.  Check this article out to view data in traditional acceleration units rather than units of displacement.

 

1.c: Low-mid frequency source (Q-LMF):


5.gifFigure 5: Detail view and specs for the low-mid frequency source.

The low-mid frequency source (Q-LMF) is ideal for producing high noise levels over a wide frequency range (sufficient for exciting fully trimmed vehicles). It outputs a calibrated volume acceleration (m3/s2).

 

As most applications of this source are often cabin applications, the device is optimized for quick-positioning on a seat, with the acoustic center at ear location. The Q-LMF operates as an omni-directional point source for acoustic excitation. The source has diffraction properties similar to that of a human body, ideal for cabin seat applications.

 

1.d: Mid-high frequency source (Q-MHF):

 

6.gifFigure 6: Detail view and specs for mid-high frequency source.

The mid-high frequency source (Q-MHF) is a general use omni-directional monopole volume acceleration source. The sound source level in combination with the wide frequency range makes the Q-MHF an extremely versatile NVH tool.

 

The tube design allows for easy placement of the point source enabling quickly moving the point source location between measurements.  It outputs a calibrated volume acceleration (m3/s2).

 

2. Structural Qsources

 

The structural Qsources are designed to emit a broad range of force (N) levels and frequencies (Hz). The structural Qsources provide a repeatable input while being easy to mount. All of the structural Q sources have a unique mounting system which allows for mounting in any direction on almost any surface (even curved surfaces). See Figure 7 below for mounting examples.

 

7.pngFigure 7: Examples of mounting the Qsources in tricky to excite areas. Left top: miniature shaker. Left middle: high frequency shaker. Left bottom: integral shaker. Right: thumper shaker.

The structural Qsources also feature decoupled mass designs, which results in minimal mass-loading of the structure under test. The decoupled mass also means that the shakers are self-aligning, and force is always applied in the shaker stinger direction.

 

The small form of the Qsources allows for mounting in narrow and tight spaces where mounting a traditional shaker (or hitting a hammer) may prove difficult. This is increasingly important as products become more complex which increases product packaging density inside of integrated systems.

 

The Siemens portfolio consists of four structural exciters:

  • Thumper shaker (Q-TMP)
  • Integral shaker (Q-ISH)
  • Miniature shaker (Q-MSH)
  • High frequency shaker (Q-HSH)

A quick comparison of the source specifications is available in the table below (Figure 8):

 

8.pngFigure 8: Overview of the specifications for each structural Qsource.

The frequency ranges and input levels of the structural Qsources are visually represented below (Figure 9).

 

9.pngFigure 9: Visual comparison of the frequency and output levels for each structural source.

2.a: Setup of the Structural Shakers:

 

All of the structural shakers are setup in a similar way:

  1. Clean the surface of the structure on which the shaker will be mounted.
  2. Adhere the shaker to the structure (either directly, or with a mounting piece, depending on the shaker).
  3. Connect the PC to the SCADAS. The PC will control the output signal using Simcenter Testlab. The PC will also store the data acquired with the SCADAS.
  4. Connect the output of the SCADAS to a power amplifier.
  5. Connect the output of the power amplifier to the electronic protection system (EPS). The EPS units protect the sources against excessive voltage and current levels.
  6. Connect the output from the EPS to the shaker input.
  7. Connect the shaker output to the input of the SCADAS system. All of the shakers have force output. The integral shaker and the miniature shaker also have acceleration output.

10.pngFigure 10: Schematic of measurement chain for the structural Qsources.

This article has more information about setting up the shakers (specifically the integral shaker). 

 

See the sections below for more detail on each structural shaker (Q-TMP, Q-ISH, Q-MSH, Q-HSH).

 

2.b: Thumper shaker (Q-TMP):

 

11.gifFigure 11: Left: Detail view. Right: Thumper shaker specs.

The thumper shaker (Q-TMP) is ideal for low frequency (5-200 Hz), high output force applications (25 Nrms). The thumper shaker is an option for applications in which an instrumented sledge-hammer is typically required, such as heavy machinery, power-generation, industrial installations, etc.

 

The shaker is self-suspending and self-aligning. No external support is required, meaning the shaker can be mounted in any direction, and the force will always be applied along the stinger axis.

 

The shaker is mounted to the structure in a two-step process:

  • First, a circular plate with an M8 threaded hole in the center is adhered to the structure.
  • Then, the shaker tip is threaded into this hole. Safety cables can be attached in-case the mounting fails.

It is possible to mount multiple threaded plates to the structure. Then, if the shaker needs to be moved between measurements, it is unscrewed from one location, and screwed into another.

 

The thumper shaker has an integrated axial force sensor, simplifying FRF measurements. The thumper shaker does not have an integrated accelerometer. If a driving point measurement is desired, it is recommended to place an additional accelerometer near the shaker excitation point.

 

The thumper shaker weights 1.0 kg. However, due to the decoupled-mass design, the effective mass loading on the structure is only 150 grams axially and 800 grams radially.

 

2.c: Integral shaker (Q-ISH):

12.gifFigure 12: Left: a detail view of the shaker. Right: Integral shaker specs.

The integral shaker (Q-ISH) delivers frequency excitation from 20 to 2,000 Hz with a 7 Nrms force level. The integral shaker is an all-around shaker for both full vehicle testing as well as component-level testing.

 

The integral shaker delivers a high force level in a compact form. The shaker is self-suspending and self-aligning. No external support is required, meaning the shaker can be mounted in any direction, and the force will always be applied along the stinger axis.

 

The decoupled mass design reduces the mass loading on the structure to just 19 grams (total shaker weight is 370 grams).

 

The shaker can be directly stud mounted to a structure using its M5 threaded stinger. In this configuration, the shaker can only measure input force.

 

Alternatively, a bell housing with an integrated accelerometer can be used. This configuration is ideal if measuring a driving point is desired. First, glue on a threaded M5 bell housing. Then, thread the shaker into the bell housing. If exciting at multiple locations, it is easy to glue on multiple housings and then simply unscrew and re-screw the shaker into different positions.

 

2.d: Miniature Shaker (Q-MSH):

 

13.gifFigure 13: Left: Detail view. Right: Miniatures shaker specs.

The Miniature shaker (Q-MSH) delivers frequency excitation from 50 to 5,000 Hz with a 2 Nrms force level. The extremely small form factor makes this shaker ideal for internal excitation of assemblies as well as low-mass components where mass loading is of concern.

 

The shaker is self-suspending and self-aligning. No external support is required, meaning the shaker can be mounted in any direction, and the force will always be applied along the stinger axis.

 

The shaker can be glued directly to the test structure and needs no external support. This makes moving the shaker to multiple input locations easy: simply break the glue bond, clean the shaker with the included tool, and re-glue to the new location.

 

Due to the decoupled-mass design, the shaker only adds 10 grams of mass loading to the structure (while the total shaker weight is 100 grams).

 

The miniature shaker features integrated force and acceleration sensors making this an ideal option for driving point measurements. 

 

2.e: High Frequency Shaker (Q-HSH):

14.gifFigure 14: Left: Detail view. Right: High frequency shaker specs.

The high frequency shaker is the smallest form shaker which delivers the widest frequency range excitation: from 500 to 10,000 Hz with a 0.8 Nrms level. The shaker has the smallest footprint, with a mounting location size of 8mm diameter.

 

The shaker is self-suspending and self-aligning. No external support is required, meaning the shaker can be mounted in any direction, and the force will always be applied along the stinger axis.

 

The shaker has a total mass of 30 grams, but due to the decoupled mass design, the shaker only adds 3 grams of mass loading to the structure.

 

The shaker is glued directly to the test object making for fast installation. 

 

The miniature shaker features an integrated force sensor. If driving point measurements are desired, it is recommended to also place a nearby accelerometer.

 

Check out this article on how the shaker survives in harsh environments!

 

2.f: Amplifier (Q-AMP):

 

The Qsource measurement amplifier has the following functionality:

  • The BNC and banana output connectors match all Qsource exciters
  • No fans or ventilators make this a low-noise amplifier (critical for acoustic measurements)
  • Excessive heat is transferred to the heatsink housing
  • High pass cutoff filter (more details below)

15.pngFigure 15: The Qsource amplifier.

The Qsource amplifier features a high pass cutoff filter. This is useful when outputting broadband noise. If an engineer wants to excite from 30 – 250 Hz, she would set her signal generator to produce white noise up to 250 Hz. By default, most signal generators and software do not output band-limited noise. Therefore, the signal generator would product white noise from DC – 250 Hz. These low frequencies waste the capacity of the source in a range that the engineer is not interested in (0 – 30 Hz).

 

The high pass filter can be used to limit the low frequency content and prevent wasting the capacity of the Qsource resulting in more energy at frequencies of interest and higher quality FRFs.

 

Questions? Email jacklyn.kinsler@siemens.com

 

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Comments
Dreamer
Dreamer

What is it about the shaker designs that reduces the mass loading effects?  Does it depend on the frequency at all?  Any small insight would be well appreciated.  Thanks in advance.

Siemens Valued Contributor Siemens Valued Contributor
Siemens Valued Contributor

 

Q-Source structural exciters have a proprietary self-suspending and self-aligning suspension design, that allows a test object to vibrate freely without influence from the total mass of the Q shaker. For example, as stated in the article the integral shakers (Q-ISH) mass loading is reduced from 370 grams to just 19 grams due to this unique design feature.

 

  • At low frequencies(<20Hz) full coupling between stinger and inert shaker mass exists, static mass of total shaker is coupled with test structure.
  • Above rigid body mode frequencies(>>20Hz), decoupling between stinger and inert shaker mass exists. Inert mass does not load test structure anymore.

                                                           See the animation below to understand this coupling:

q4.gif

 

As you see demonstrated in the animation as the excitation frequency is increased the inert mass is isolated from the test object.

 

 

Furthermore, tuned internal spring stiffness and inert mass support locations enables precise force generation in stinger direction with very limited sag.

 

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