FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

- 147 -
Figure 3 shows a block diagram of the prototype system currently under
development. This system may be considered a redeployment of the
components that make up an advanced conventional multi-channel A/E monitor;
but the advantages that accrue to continuous monitoring of large
structures, to advanced signal analysis, and to reduced system hardware
cost are substantial.
Similar to seismic laboratories located about the earth, this system uses
acoustic emission surveillance units located about a subject large
structure. The surveillance unit is capable of a variety of A/E signal
processing tasks. The current prototype is designed to measure six A/E
parameters that are dealt with during conventional A/E analysis. With the
advent of digital signal processing techniques, subsequent units will have
a variety of enhanced capabilities enabled by this technology.
A surveillance unit is placed in close proximity to each A/E transducer.
In some applications the transducer may be installed within the
surveillance unit enclosure, thus simplifying installation and minimizing
the risks to low level analog signal transmission. The surveillance unit
consists of three electronic subsystems. These are:
a) Analog section for A/E signal processing; the
b) Digital section for measuring A/E transient parameters; and the
c) Microprocessor section which controls the function of the surveillance
unit, may perform some A/E data processing and storage, and transmits
this data to a central control point.
Data transmission is possible by several mechanisms, the most common using
wires to conduct electronic signals. This concept is not restricted to
hard wired systems, but the prototype under development will use a four
wire Modem type data link.
The control point for a network of surveillance units will vary between a
simple status indicator display, to mini computer based data collection and
analysis facilities. Generally, as the complexity of the structure
increases, or as the number of variables that affect the acoustic emission
regime increases, the required computing facility will increase. To
illustrate this, the required central computing facility to monitor the
operation of several valves would be less complex than that to monitor the
acoustic emissions from an offshore platform (the number of A/E transducers
being the same in both cases).
This equipment deployment scheme essentially supports the two levels of
software necessary when establishing the interpretive functions of a
continuous A/E monitoring system. It is the interpretive function that: