The instrumentation

The high luminosity of the instrument with no slits to limit the size of the beam. This is the Jacquinot s advantage also called etendue. ... 

An improved signal/noise ratio because all signals are seen simultaneptisiy along with the instrument s own noise (called the multiplex or Fellgett advantage). 

Fokker Bond Tester. An ultrasonic inspection technique commonly used for aircraft structures is based on ultrasonic spectroscopy [2]. Commercially available instruments (bond testers) used for this test operate on the principle of mechanical resonance in a multi-layer structure. A piezoelectric probe shown in Figure 3b, excited by a variable frequency sine signal is placed on the surface of the inspected structure. A frequency spectrum in the range of some tens of kHz to several MHz is acquired by the instrument, see Figure 3a. 

During the inspection of an unknown object its surface is scanned by the probe and ultrasonic spectra are acquired for many discrete points. Disbond detection is performed by the operator looking at some simple features of the acquired spectra, such as center frequency and amplitude of the highest peak in a pre-selected frequency range. This means that the operator has to perform spectrum classification based on primitive features extracted by the instrument. 

Very many types of eddy current instruments available tend to look remarkably similar in much the same way as automobiles tend to look alike. This may be an inevitable trend since developments are converging on users needs, plus PC platforms are being used more and these too are tending to look more and more alike. In the way that the DSP has changed the inside of the instrument, the PC. is changing the outside. 

Modularity problems the instrument includes many different boards which are very well made for standard applications, but it is sometimes diffieult to set up a new type of examination. For example use of multiple probe, or multi-elements probes. 

Hardware problems as the instruments have rather poor processors and custom architecture, it is difficult to test new configurations and, once the new configuration is selected, it is often necessary to strongly modify the hardware in order to adapt the existing instruments. 

Blackout problem if the instrument does not properly work, it is difficult to observe intermediate states. Very sophisticated instmmentation is needed to measure voltages, currents or logical levels on the boards of the instrument. 

Limited capabilities as the instrument carries out an analog measurement, on-line signal processing of data is almost impossible. All analysis tasks must be done off-line, and cost is increased (equipment, specialists). 

The instrument uses a sinusoidal driver. The spectrum is very clean as we use a 14 bits signal generator. The probe signal is modulated in amplitude and phase by a defect signal. The demodulation is intended to extract the cartesian values X and Y of this modulation. 

The main danger when using so much software is to never know if the version used is up to date. This problem was solved by identifying each software and hardware component of the instrument. 

Without opening the instrument, the user can know the configuration (how many boards, probe-module, controller module) and software identification. 

In non-destructive testing, there are almost as many procedures, needs or uses as users it is therefore important to be able to quickly modify the instrument in order to answer a new request. This new architecture is meant for such operations. 

Also a very important the instrument may be adapted to a customer s needs by only changing software, and handing a floppy disk to the customer. Even better, the customer himself can download the software from our server, using a modem or the Internet. 

The contribution that Hocking wished to make was to refine the sensor system and the instrumentation paekage so as to be able to incorporate the necessary functionality within a lightweight portable battery operated instrument. This implied a lower power level and very low-noise instrumentation. We aimed also for a low cost instrument able to operate for several hours from fully charged batteries and able to operate at a pull speed of 500mm/second. 

The probe receives a signal when either the driver or detector coil passes a flaw or other feature in the tube A signal is produced over the full length of the flaw. It is affected by geometry and permeability changes which cause the instrument zero to wander. 

The research [5] showed the inspection records fulfilled by different instruments are very close each other. Nevertheless some of the instruments are able to put an information out to a computer, main inspection records usually are performed as chart diagrams of the LMA and LF channels. 

This is a double-channel flaw detector having their own microcomputer with 1 Mbyte memory to store data of the LMA and the LF channels for 800...2000 m of a rope under inspection. The instrument can be used in two modes as a tester for operative inspection or as a device for the inspection data storage. 

Calibration procedure bases on rope specimens and corresponds to the Standard Pratice ASTM 1574. It takes a piece of the rope under test having a nominal metallic cross-section area (LMA=0) to set zero point of the instrument. Rope section with the LMA value known is used to set the second point of LMA calibration charactiristics. It is possible to use the air point calibration when there is no rope in a magnetic head (LMA=100%). 

The INTROS Flaw Detector is certified by the Russian State Standard Service (GOSSTANDART) as well as approved by the Russian State Mining and Technology Safety Inspection (GOSGORTECHNADZOR). It is used to inspect mining hoist and crane ropes. Fig. 5 illustrates the INTROS use at the mining hoist of an Ural ore mine. The previous model of the instrument, MDK-11 was used to inspect ropes of the air rope ways in Caucasus and Kazakhstan in 1996. Fig. 6 shows the INTROS MDK-11 inspection of 45 mm skyline rope in Almaty, Kazakhstan. 

The instrument prevents automatically from interfering factors. 

The instrument has 6 working frequencies to choose the depth of test. 

In summer 1998 the instrument will start with first measurements. 

During testing a depth resolution of 50-80 micron and a lateral resolution of 20-40 micron was achieved. The spatial resolution was limited not mainly hy source or camera properties, but by the accuracy of compensation of the instrumental errors in the object movements and misalignments. According to this results a mote precision object rotation system and mote stable specimen holding can do further improvements in the space resolution of microlaminography. 

It should be noted that these results are only preliminary and have to be considered as a proof of concept. As is clear from eq. (2) the phase contrast can be improved drastically by improving the global resolution and sensitivity of the instrument. Currently, a high resolution desktop system is under construction [5] in which the resolution is much better than that of the instrument used in this work, and in which the phase contrast is expected to be stronger by one order of magnitude. 

At the same time advisability of designing the instrument taken into consideration cracks length 1 and object thickness T and of defining the instrument application sphere can be only determined after research work. 

Fig. 1 shows the block diagram of the vibrometer, in which the most sensible to small phase variations interferometric scheme is employed. It consists of the microwave and the display units. The display unit consists of the power supply 1, controller 2 of the phase modulator 3, microprocessor unit 9 and low-frequency amplifier 10. The microwave unit contains the electromechanical phase modulator 3, a solid-state microwave oscillator 4, an attenuator 5, a bidirectional coupler 6, a horn antenna 7 and a microwave detector 11. The horn antenna is used for transmitting the microwave and receiving the reflected signal, which is mixed with the reference signal in the bidirectional coupler. In the reference channel the electromechanical phase modulator is used to provide automatic calibration of the instrument. To adjust the antenna beam to the object under test, the microwave unit is placed on the platform which can be shifted in vertical and horizontal planes. 

These two transducer pairs are activated alternating. For this purpose an ultrasonic instrument is combined with a two channel multiplexer. Figure 8 presents a modified standard instrument USN52 which also implies a modified software. This system performs four measurements per second - alternating the velocity and the thickness are determined. The probe can be scanned over the surface and in every position both, the velocity and the wall thickness are indicated Using the serial interface of the instrument finally a two-dimensional map of velocity or thickness can be generated. 

The ultrasonic instrument will be set up according to the test specification in the common way. Connection of the instrument to the ISONIC extends the flaw detector performance instrument to a reliable ultrasonic testing system which provides full documentation of the scan. 

Input of the test object-related data with automatic transfer of the instrument adjustment data (via RS 232)... 

Since any DAC is defined by its coordinates P (Ai,S ) and the instrument sensitivity Gg f (reference gain) during DAC recording, any recalculation of the curve including the consideration of individual corrections (transfer loss, sound attenuation, etc.) is an easy task for modern PC based flaw detectors and does no longer burden the operator. 

The curve is defined by the Amplitude/Distance pairs P,(Aj,S ), documented in a corresponding DAC table and stored in the instrument s memory. 

The echo amplitude Ar of a reference reflector depends on the type, size (diameter) d f, and distance Sr,., of the reference reflector, and additionally on a possible attenuation in the reference block and finally the absolute gain setting of the instrument G f. In a combined DAC/DGS evaluation program we define the following ... 

Absolute instrument gain at which the maximised reference echo reach 80% screen height. After DAC or reference echo recording the instrument gain is automatically... 

Even now the operator should be able to change the instrument sensitivity, e.g. to evaluate an echo which exceeds the upper limit of the screen, or which is too small, or simply to follow the mles of the test specification requiring a so-called search sensitivity. Even after changing the gain, any echo evaluation will be correct, since the registration curve will be adjusted automatically to always maintain the correct relationship between the defect echo and the registration curve. 

We are confident that any user of this combined evaluation technique, as well as the development of future test standards for manual ultrasonic testing will benefit from this result, because it allows a greater flexibility in the applicable method without loosing reliability. Often an expensive production of a reference block can be avoided and therefore testing costs are reduced. Since all calculations are performed by a PC, the operator can fully concentrate on his most important duty scanning the workpiece and observing the A-scan. Additional time will be saved for the test documentation, since all testing results are stored in the instrument s memory (the PC s hard drive) with full link to the Software World (Microsoft Word, Excel, etc.). 

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