From sensor to turnkey system,an answer for each need
ACOUSTIC EMISSION SENSORS
The
single most important factor in acoustic emission (AE) testing is
the selection of the AE sensor (transducer). Physical Acoustics
Corporation prides itself on its ability to continually design and
manufacture a diverse line of quality high sensitivity / low noise
sensors to meet your particular needs. This capability is based on
our solid tradition and expertise in the field of AE applications,
which began with Dunegan Corporation in 1968.
. Our
sensors actually "listen" to structures and materials to detect AE
activity. Pressure vessels, storage tanks, heat exchangers, piping,
reactors, aerial lift devices, and nuclear power plants are among
the most common types of structures that are monitored. In all
applications, AE sensors are vital links between the test structures
and the analysis instrumentation, and their performance is critical
to the success of every test.
AE sensors are available from PAC in various sizes,
shapes, frequency and temperature ranges, and packaging styles n
order to meet the diverse needs of the application and environment.
Browse our list below, or
learn more about sensor calibration and selection.
Specifications & Features subject to change without
notice
Download our entire sensor chart!
The piezoelectric effect, first demonstrated by the Curie
brothers in 1880, occurs when pressure applied on a crystal with unit
cells that exhibit no center of symmetry will develop an electric field,
or conversely, a mechanical deformation will occur at the application of
an electric field. The design of PAC's sensors (transducers) is structured
upon the optimization of several piezoelectric parameters coupled with our
know-how of delicate final assembly.
The make-up of a
typical AE sensor along with its piezoelectric element, in this case a
crystal (Figure 1). Characteristic evaluation of the piezoelectric
element, is dependent on the accurate measurements of density, size,
clamped capacitance and low field dissipation facto. We inspect and
control all relevant parameters of our piezoelectric elements (along with
ascertaining their impedances and critical frequencies per IEEE standards)
because we manufacture them. At PAC, our sensors are designed by AE
engineering specialists.
Physical
Acoustics sensors are either single-ended (S) or
differential (D) in construction. The single-ended design employs a single
crystal to provide high sensitivity and omni-directional response,
regardless of orientation to the AE excitation. The differential designs
provide common mode rejection of unwanted signals in environments of high
electromagnetic interference. The output of a differential sensor is
processed by a differential amplifier to provide 24dB common-mode
rejection.
In
our sensor manufacturing facilities, quality materials and workmanship
combine to produce reliable, high-performance sensors. These sensors are
handcrafted by skilled and experienced assemblers who consistently produce
superior units. The sensor housing and integral electronics are designed
to eliminate RFI/EMI and microphonic interference.
AE
Sensor Calibration:
Calibration,
traceable to the U.S. National Institute of Standards and Technology
(NIST), formerly NBS, is the important final element of the manufacturing
process. A sensor's response during a test can be predicted by its
frequency response, provided that an appropriate calibration method is
used. Recognizing this fact, NIST developed the surface wave calibration
method. This procedure subjects the sensor to a surface wave similar to
that of an actual AE event.
Physical
Acousticscalibration uses either the NIST Transient Surface Wave
Calibration (ASTM E1106-86, Standard Method for Primary Calibration of AE
Sensors) or the White Noise Continuous Sweep method(ASTM E976-84, Standard Guide for Determining the
Reproducibility of AE Sensor Response), otherwise known as the
Face-to-Face Technique.
All Physical
Acousticssensors come with a
certificate displaying characteristics and method of calibration. The
Transient Surface Wave Technique is ideal for AE burst applications.
Sensitivity is expressed in voltage output per vertical velocity vs.
frequency. The Face-to-face Technique is based on voltage output per unit
of pressure input and is recommended for continuous AE monitoring
applications. The frequency response is used to select the proper filters
for the preamplifiers and the analysis instrumentation.
Mounting a Sensor:
An essential requirement in mounting a sensor is sufficient
acoustic coupling between the sensor face and the structure surface.
First, make sure that the sensor's surface is smooth and clean, allowing
for maximum couplant adhesion. Application of a couplant layer should be
thin, so it can fill gaps caused by surface roughness and eliminate air
gaps to ensure good acoustic transmission. The sensor should be held
firmly to the testing surface at all times. Commonly used couplants are
vacuum greases, water-soluble glycols, solvent-soluble resins, and
proprietary ultrasonic couplants.
In addition to coupling, the sensor must always be
stationary. One way to achieve this is to use glue, which can also
serve as a couplant. Before using a glue, consider the ease and
technique of removal, since not all sensors can withstand a large
removal force between the housing and the mounting face (wear
plate). To prevent attenuation, avoid air bubbles and thick glue
layers. Another way to help a sensor stay stationary, is to use a
holding device such as tape, elastic bands, springs, magnetic
hold-downs, and other special fixtures. Caution: Make sure that any
mechanical mount used does not make electrical contact between the
sensor case and the structure.
Other sensor mounting precautions lie in whether the mounting surface is
either very hot or very cold. Typical couplants may be unstable on hot
surfaces or may freeze solid and debond on cold surfaces. A metal rod
which conducts the acoustic signal for the hot or cold structure to the
sensor at an ambient temperature, called a waveguide, is a common
solution.
Summary:
Physical
Acoustics sensors have been custom designed for use on
various structures and accommodate almost all of the varying conditions
presented in AE testing. As applications for AE testing expand, PAC
designers develop new sensors to meet newly-identified consumer needs.
Whatever the application, PAC acoustic emission sensors are there
listening!
Opened systems: DLL 32 bit, Labview, Visual C++
drivers
for the development of your special applications
Home>
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sensors
Our
sensors actually "listen" to structures and materials to detect AE
activity. Pressure vessels, storage tanks, heat exchangers, piping,
reactors, aerial lift devices, and nuclear power plants are among
the most common types of structures that are monitored. In all
applications, AE sensors are vital links between the test structures
and the analysis instrumentation, and their performance is critical
to the success of every test.
