Short presentation of some of the unique features of the system.


Please observe that the DELTATEST -system is not based on one unique principle only. Basically every function block contain unique principals and circuit solutions, developed by TÖRNBLOMS KVALITETSKONTROLL, which togehter contribute to the system's characteristics and excellent measuring performance. TÖRNBLOMS KVALITETSKONTROLL supply tailor-made solutions !


1. MATERIAL TYPES

The system can be used for practically all metallic materials.


2. MULTIPLE CHANNEL DESIGN

The system can consist of several parallel channels, with same or different measuring purposes: defect detection, distance measuring, surface structure measuring.


3. SENSOR DESIGN PRINCIPLES

High amplification factor with low noise. Differential (D), absolute (A) or (D+A) types. New sensor power supply design: Minimum losses in sensor coupling = high efficiency.


4. STABILITY

Automatic phase stability adjustment of electronic enables high frequency selection.


5. FREQUENCY CONVERSION (SELECTIVITY)

A newly developed frequency conversion function improves selectivity performance approx 20 times!


6. PHASE DISCRIMINATION

Conventional phase controlled rectifiers have bad phase selectivity. Instead the DELTATEST -system is based on (option) advanced VTF-technique for increasing vector phase angles and improving phase selectivity:

Product-Quotient-Formation (PD-PQ), improving phase selectivity.

Amplified phase difference (PD-PE), widening vector phase angles.


7. ADAPTIVE PHASE ANGLE ADJUSTMENT

Phase angle variations in the sensor signals, caused by variations in the test object's material properties or temperature, can generate phase errors and cause fault signals.
The DELTATEST -system has a "build-in" adaptive compensation curcuit (option), which automatically eliminate these phase angel variations.


8. SIGNAL OFF-SET ADJUSTMENT

The sensor signals are automatically and continuously balanced to zero-level, using electronic control servos. These servos have been used and developed throughout many years and include separate functions for minimising possible drifts, which make them very suitable for measuring togheter with sensors of the absolute type.


9. FILTER FUNCTIONS

Crack signals look initially like pulse signals. The theory for the most common active filters presupposes continuous signals for best filter characteristic. Consequently, this filtertype is not suitable for pulse applications like crack detection systems.

The DELTATEST-system uses unique filter design principles, based on time delayed signals and special filters for pulse applications. As contrary to conventional LP, BP, and HP-filters, these specially designed filters can show high Q-values for single pulses, which strongly improve the filter characteristics for actual applications.


10. DYNAMIC TRANSFORMATION, DT

This function automatically and dynamically fine-tune the Vector Transformation circuits as a function of a specific parameter, e g Lift-Off - distance. The dynamic transformation was introduced in the first hot-inspection system 1986 and is one important reason for consistent performance.


11. SUPPRESSION OF VIBRATIONS

In applications, where vibrations in the test object are frequent and normal, conventional Eddy Current system will produce false signals, often to an unacceptable level.
The DELTATEST-system is an exception, because it a capability to suppress these process vibrations, thanks to a combination of following well-proven functions:

• Unique sensor design
• Special pulse filters
• Advanced Vector Transformation
• Filter based on time delay
• Unique phase discriminating technique
• Special signal balancing and off-set functions

12. SUPPRESSION OF (LIFT-OFF) DISTANCE VARIATIONS

The crack signal from the sensor varies in size at varying distances between sensor and object (changed inductive coupling results in impedance variations). For accurate measuring, many Eddy Current systems achieve a constant Lift-Off-distance by using support wheels, which is limitation in most hot on-line applications.

The DELTATEST-system, however, includes functions (option) which automatically and dynamically adjust the fault-signals to a correct value, within a relatively large working range. The consequence of this is that the measurement can be done contact less.
This feature of being able to supress rapid distance variation to the surface, also open up possibilities to scan circular (round) surfaces.


13. SUPPRESSION OF OSCILLATION MARKS (OSCM)

Using a sophisticated phase discriminating technique in combination with the unique vector transformation, the system will supress surface irregularities of the scanned object. This has been demonstrated in three hot on-line slab inspection installations.
As an example, OSCM as deep as 2 mm are surpressed using a standard sensor, while 1 mm deep cracks still can be detected. As far as we know, no other system (?) on the market can do that.

Instead of suppressing these irregularities, they can be amplified and measured by this function "inverted", to produce a surface irregularity index.


14. SEPARATION OF DEFECTS, ADJACENT TO EACH OTHER

The system is equipped with high speed off-set curcuits, which automatically prepare the in-put curcuits for a new signal evaluation from upcoming defects, so that "old" defects do not affect the evaluation of a "new" ones.


15. QUEUE FUNCTION

If inspected test objects have local areas with many defects, a special comparative function will save information from larger defects at the expence of smaller defects, when "queue-problem" arise.


16. CLASSIFICATION OF DEFECT TYPES

Development is underway to use "two-dimesional" measuring technique, i.e. evaluation of a single crack signal will be done with respect to amplitude as well as phase-angle.
By doing so, a special index can be formed, which then will assume different values for different types of defects.