Table of Contents ECNDT '98
Ultrasonic PC- Boards for different ApplicationsDr.-Ing. W. Hillger, (German Aerospace Center), Institute of Structure Mechanics
Lilienthalplatz 7, D-38108 Braunschweig, Germany
Telephone +49 531 295-2306, Telefax +49 531 295-2875
|TABLE OF CONTENTS|
In order to use the high performance resources of Personal Computers directly for ultrasonic inspections, PC-pulser/receiver boards were developed. A wide range of materials require different pulser/receiver boards HILL-SCAN 30XX, which enable ultrasonic inspections from 30 kHz to 35 MHz with a signal to noise ratio up to 60 dB. Dependent on the application (manual testing or imaging), different ADC- boards with frequencies up to 400 MHz (single-shot) are used. Software is available for all inspections. Typical applications are: material characterization and -testing (concrete, components of nuclear power stations, welded joints, new materials and thin layers), ultrasonic imaging and transducer qualification.
The rapid development of the computer technique and the decreasing prices in spite of the increasing of performance have spread the use of personal computers (PCs) not only for industrial use but also for private use. Also, in spite of increasing requirements measurement and test systems become more and more economical , including NDT-systems.
In order to be able to reduce prices, even more and more test- and measurement systems are integrated on PC-boards. The powerful and inexpensive PC components can be directly used for these (virtual) instruments. The limited dimensions of the PC boards require a reduction to the absolute necessity of the electronic components. Analogue signal processing must carried out by software as far as possible.
We decided already in 1994 to develop PC boards for ultrasonic inspections [1, 2].
The requirements for an ultrasonic PC-board depend on the material and the dimensions of the component and on the type of inspection (manual or automatic inspection, with or without imaging).
Materials to be inspected are, for example: Concrete with test frequencies of about 50 kHz, sandwich components with 500 kHz, metallic materials up to 10 MHz and thin components up to 35 MHz. Apart from the difference of materials, variable thicknesses and attenuations require different amplifications and signal processings.
In order to obtain a high signal-to-noise ratio sufficient acoustical power is necessary. For special applications a programmable pulser (transmitter) is required in order to optimize the frequency spectrum.
Additional requirements have to be met, such as norm DIN 25450 for manual testing. This norm describes the requirements of transmitters, receivers and other parts of the system.
For ultrasonic imaging systems (B-, C- and C-scans) single-shot measurements, fast data recordings, and fast data transfer must be performed.
The ultrasonic hardware has to be designed to fit the PC boards. The length of the board should only be 160 mm for convenient installations because memory modules and processor cooler can be located behind the 160 mm long slot connector on the motherboard.
Apart from the technical data, the customer expects good price/performance-ratio.
|Fig 1: Ultrasonic pulser/receiver PC-board|
The HILL-SCAN boards contain the following subsystems:
|HILL-SCAN type||Highlights||Frequency range|
|3010||Ultrasonic inspections up to 20 MHz||0.1 to 20 MHz (-3 dB)|
|3010 HF||High bandwidth, high resolution||0.01 to 35 MHz (-3 dB)|
|3011 NF||Optimized for materials with high sound damping||0.01 to 10.5 MHz (-3 dB)|
|3020 LOG||Logarithmic amplifier with 60/100 dB dynamic range without gain setting||0.1 to 10 MHz (-3 dB)|
|3040 DAC||DAC (distance amplitude control) up to 40 dB|
optimized for material with high sound damping
|0.1 to 20 MHz (-3 dB)|
|3041 NF||Echo-technique for concrete DAC up to 40 dB|
optimized for material with high sound damping
|0.01 to 10 MHz (-3 dB)|
|3050||optimized for back scattering, built - in video rectifier with peak hold||15-20 MHz, bandpass filter customer specified|
|3100||programmable pulser, rectangular/ burst- signals, for materials with high sound damping||centre frequencies: 50 kHz to 6 MHz|
The VMOS-pulser with a rise time lower than 6 ns provides high axial resolution and high-frequency inspections above 10 MHz with an excellent signal-to-noise ratio. The output voltage amounts to about 228 V without load, and 194 V with a load of 75 Ohm. A damping control from 75 Ohm to 360 Ohm matches the impedance to the transducer.
The pulser/receiver is completely shielded and therefore receives no noise coming from the PC components. The input connector is a Lemo 00 coupler. The extremely low noise amplifier with a maximum amplification of about 90 dB accommodates very small signals. A precise gain setting is possible up to 106 dB.
In order to get an extremely high resolution and a small "dead zone" (after the transmitter pulse) single amplifier states must have a bandwidth up to 90 MHz (!), and a total bandwidth of 35 MHz (-3 dB) can be reached (HILL-SCAN 3010HF). High- and low-pass filters can be combined to band-passes and provide optimal A-scans. All parameters are controlled by software.
External Trigger Input
The external trigger input allows automatic inspections and ultrasonic imaging. The clock signal of an encoder or of stepper motors can be used as a trigger for the pulser. An internal software controlled divider allows different scan resolutions.
Programmable Pulser HILL-SCAN 3100
The transmitter board HILL-SCAN 3100 provides a higher acoustic energy than the usual spike pulsers. It generates rectangular pulses with programmable widths from 0,16 to 2,4 µs, or rectangular burst signals from n = 2 to n = 10. Frequency and bandwidth of the transmitter pulses can be set over a large range. The usable frequency range is about 50 kHz to 5 MHz.
In testing materials with high sound damping, the burst transmitter increases the signal-to- noise ratio to, typically, 12 dB. Typical applications: honeycomb and concrete components, and air-coupled testing.
The sample frequency of the ADC (analogue to digital converter) should be 8 times higher than the test frequency (centre frequency of the spectrum). In dependence of the application, different ADC- boards are used. A standard board (20520) provides 8 bit resolution and up to 100 Msamples/s in single shot mode. For manual tests, up to 400 Msamples/s can be reached in the repetition mode. For scanning systems with high frequencies boards up to 400 Msamples/s (single shot) are available.
The software US-SCAN 3.0 (IBT GmbH, Ober-Ramstadt, Germany) provides all functions of a portable flaw detector and a powerful ultrasonic imaging in A-, B-, C- and D-scans. Not only motor driven scanners can be used, but also manual scanning systems with encoders. Further documentation and test reports can be carried out with WindowsTM software.
Special software (HILLGUS) was also developed for material characterizations such as the determination of the modulus of elasticity for building materials.
The HILL-SCAN 30XX boards can be used in different PCs. Desktop- and tower-PCs as well suited for laboratory uses. For in-field inspections rugged notebooks and portable PCs are advantageous. A typical portable system is shown in Fig. 2 (USPC 3010), used in MUSE (Mobile UltraSonic Equipment). This portable PC not only contains the boards for ultrasonic testing but also a controller with power supply for stepper motors, so that a manipulator can be connected directly. The MUSE system is enlarged with a water circulation system which enables a "local immersion technique" for in-field inspections. A typical result is shown in Fig. 3, which presents a D-scan of a CFRP- component in RTM-techniques. The defect area caused by an impact is clearly indicated. The manipulator is described in .
|Fig 2: Portable PC used as ultrasonic system||Fig 3: D - Scan of an impacted RTM - panel (MUSE with HILL - SCAN 3010)|
Fig. 4 presents an A-scan of a 0,15 mm thick steel plate. The RF-A-scan (sampled with 400 MHz) clearly separates the backwall echoes and demonstrates the high resolution of the HILL-SCAN 3010HF with a 50 MHz transducer.
Fig. 5, also an A-scan, shows the possibility of the echo-technique for concrete. The interface and backwall-echo of a 20 cm thick concrete specimen are displayed (RF-display). A HILL-SCAN 3041NF board and a broadband transducer (40mm element ø) are used which enable optimal pulse parameters in a range of 50 to 150 kHz. Remarkable for concrete inspections is the high signal-to-noise ratio of about 18 dB.
|Fig 4: A-scan of a 0.5 mm steel plate (RF-recording) with 400 MHz sample frequency (HILL-SCAN 3010HF), 0.1 V/div. and 100ns/div.||Fig 5: Echo-technique for concrete inspections with HILL-SCAN 3041NF; interface- and backwall echo of a 20 cm thick concrete specimen, 0.1 V/div. and 20µs/div.|
Fig. 6, a B-scan of a 15 mm thick sandwich with Nomex cores and GFRP-skins, shows clearly the depth of the two defects in the core 4. A HILL-SCAN 3010 board and a broadband probe (0,8 to 3 MHz) were used. In regions without defects, the backwall-echo is indicated.
|Fig 6: Bt-scan of a sandwich specimen with defect (HILL-SCAN 3010)|
In order to test a wide range of materials a series of ultrasonic pulser/receiver boards has been developed. In combination with an ADC-board (analogue-to-digital converter) a PC can be converted to a high performance ultrasonic system not only for manual testing but also for automatic testing and imaging systems. The HILL-SCAN 30XX boards enable ultrasonic inspections from 50 kHz (concrete inspections) to 35 MHz (inspection of thin layers) with a signal to noise ratio up to 60 dB. The gain setting range of the receiver is 106 dB. High- and low pass filters in the receiver can be combined to band-passes, so that optimal A-scans are displayed.
The internal pulser generates an output voltage of 228 V with a rise time of lower than 6 ns, which provides high resolution for frequencies above 10 MHz. The external trigger input enables synchronization with manipulators.
The ADC boards used for the PC systems provide a resolution of 8 bit with single-shot sampling of up to 400 Msamples/s.
The HILL-SCAN 3020LOG with a logarithmic amplifier provides A-scans with a single-shot dynamic range of 100 dB.
The HILL-SCAN 3041NF board is optimized for low test frequencies so that materials with high sound damping such as concrete can be successfully inspected by the echo technique.
For special applications such as air coupled testing a special programmable transmitter board was developed. This transmitter generates rectangular and burst signals, which increase the acoustical power in an optimized frequency range, and provides a superior signal-to-noise ratio.
The great advantage of installing an ultrasonic system in a PC is that both the hardware (processor, grafics, power supply, ..) and the software (evaluation and documentation) are directly available for the inspections.
The pulser/receiver HILL-SCAN 30XX boards satisfy DIN 25450. Typical applications are: ultrasonic imaging systems for nuclear power stations and for aircraft, material characterization, transducer qualification, replacement of portable flaw detectors (inspections of welded joints), inspection of new materials, measurement systems with air coupling.