Page 206 - CW E-Magazine (26-9-2023)

Special Report

the first company that specializes in the
production of AE equipment(8).

Typical AE apparatus consist of the
following components:
Sensors used to detect AE events;
Preamplifiers amplifies initial sig-
nal – typical amplification gain is
40 or 60 dB;
Cables transfer signals distances up
to 200-m to AE devices – they are
typically of coaxial type; and
Data acquisition device performs
filtration, signals’ parameters evalua-
Fig. 4: AE detection/monitoring system tion, data analysis and charting.

Figure-6 shows the schematic
diagram of the AE instrumentation.

The purpose of AE sensors is to
detect stress waves motion that cause
a local dynamic material displacement
and convert this displacement to an elec-
trical signal. AE sensors are typically
piezoelectric sensors with elements
made of special ceramic elements like
lead zirconate titanate (PZT). Mechani-
cal strain of a piezo element generates
an electric signal. Sensors may have in-
Fig. 5: AE caused by defect/leakage in an object ternally installed preamplifier (integral
sensors). Other types of sensors include
Preamplifiers Main amplifiers Measurement
Sensors Computer capacitive transducers, laser interfero-
with filters with filters Circuitry
meters(8, 9).

Acquistion Data Figure-7 shows different types of
software storage AE sensors used for inspecting pres-
sure vessels.

Data presentation The characteristics of AE sensors
are described below and the typical
Fig. 6: Acoustic Emission Instrumentation AE signal of lead break and the corres-
ponding power spectrum is shown in
Figure-8:
Typical frequency range in AE
applications varies between 20 kHz
and 1 MHz.
Selection of a specific sensor
depends on the application and type
of flaws to be revealed.
Regular piezoelectric Integral piezoelectric
sensor Preamplifier 60 dB sensor There are two qualitative type of
Fig. 7: types of AE Sensors sensor according to their frequency

206 Chemical Weekly September 26, 2023

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