AS ISO 15549:2020 pdf free.Non-destructive testing一Eddy current testing一General principles.
Commonly used measurement modes are:
a) Absolute measurement.
The measurement of the deviation from a fixed reference point. The reference point is defined by a calibration procedure and can be generated by a reference voltage or coil. This technique can be used for sorting a product into classes based on physical properties (such as hardness), dimensions or chemical composition. It can also be used for the identification of continuous or gradually changing discontinuities.
b) Comparative measurement.
The subtraction of two measurements, one of which is taken as a reference. This technique is normally used to sort a product into classes.
c) Differential measurement.
The subtraction of two measurements made at a constant distance between the measurement locations and on the same scan path. This measurement technique reduces the background noise due to slow variations in the product to be tested.
d) Double differential measurement.
The subtraction of two differential measurements. This measurement technique provides high- pass filtering of a differential measurement independent of the relative speed between the probe and the product to be tested.
e) Pseudo-differential measurements.
The subtraction of two measurements made at a constant distance between the measurement locations.
8 Equipment
8.1 Examination system
The examination employs an eddy current instrument, one or more probes and interconnecting cabling. This combination, together with any mechanical equipment and peripheral units for data storage, etc., forms the examination system.
All essential parts of the system shall be defined in the relevant application document (see 13.2) or in a written procedure agreed at the time of enquiry and order.
Factors to be considered include:
— the type of material from which the product was manufactured and its metallurgical condition;
— the shape, dimensions and surface condition of the product;
— the purpose of the measurement, e.g. detection of cracks or determination of thickness;
— the types of discontinuity to be revealed and their position and orientation;
— the environmental conditions under which the examination is to be performed.
8.2 Eddy current instrument
The choice of eddy current instrument depends on the purpose of the examination. Of particular importance are the adjustable parameters of the instrument, the range of such parameters and the type of signal representation.AS ISO 15549 pdf download.