filial NDT Korean group in UAE & CIS
EMAT Guided Wave Circumferential Inspection System
flaw detector of the EMAT System The 8-Channel EMAT equipment consists of two main components described below.
1. Base Unit, including: • Synthesizer board • Burst generator board (frequency range: 0.4 - 4MHz); burst length (number of cycles) and frequency are adjustable via PC • Four receiver boards with eight delayed receiver channels (delay time of all channels can be modified separately), including preamplifier and filters • Output amplifier and video unit (LCD color monitor) • AT-compatible PC for system parameter control • Power supplies
2. Front End, including: • Eight transmitter power stages for EMAT transducers or transmitter and receiver boards for piezoelectric transducers • Transducer(s) and transducer cable(s) • Power supplies
General System Data
• Frequency range....................................................0.4 to 4.0MHz,
adjustable in 10kHz increments
• Burst duration..........................................................1 - 15 cycles, adjustable in 1 cycle increments
• Pulse repetition rate .................................... 2500µsec to 20msec, adjustable in 1µsec increments
• Delay time ................................................................ 0 to 25µsec, adjustable in 25nsec increments
• Total amplification .......................................................... 50dB, 40dB adjustable in 1dB increments
Controllable System Functions:
• Trigger mode selection................................................................internal, external, software trigger
• Transducer selection...................................................................2x 4-segments, or 1x 8-segments
• Pulse repetition rate and ultrasonic frequency • Number of cycles/burst
• Delay time for each transmitter and receiver channel
• Filter selection.......................................................... 0.4 - 1.3MHz, 0.8 - 2.3MHz and 2.0 - 4.0MHz
• Frequency settings....................................................................................................... 0.4 to 4MHz
• Burst duration...................................................................1 - 15 cycles, adjustable in 1 cycle steps
• Receiver attenuator .............................................................. 30dB, adjustable in 10dB increments
• Receiver amplifier ................................................................... 40dB, adjustable in 1dB
Increments
Transmitter Data
•Transmitter output impedance..............................................................................................8 to 9Ω
•Transmitter current ...................................................................................30 APP (impedance 22Ω)
•Transmitter output voltage (open circuit).............................................................................. ≈1kVPP
• Transmitter output short circuit protected for burst signals
Receiver Data
•Pre-amplification ..................................................................................................................... 30dB
• Amplification................................................................... 50dB; 40dB adjustable in 1dB increments
• Noise level of summation signal at output....................100 mV (for band-pass filter 0.4 - 1.3 MHz)
• 3 selectable band-pass filters (-3dB)........................ 0.4 - 1.3MHz, 0.8 - 2.3MHz and 2.0 - 4.0MHz
• Bandwidth (-3dB) ......................................................................................................... 0.4 to 4MHz
•Input,output impedance............................................................................................................50Ω
•Preamplifier input sensitivity.................................................................................................... 50µV
• Main amplifier input sensitivity........................................................................................ 1.5 to 2mV
•Maximum RF-signal amplitude output.................................................................................... 10VPP
Signal Modes and Delay Times
•Transmitter mode................................................................................................................... digital
• Receiver mode......................................................................................................................analog
• Maximum delay time .....................................................................50µsec fixed, 25µsec adjustable
•Minimum delay time .............................................................................................................50µsec
Trigger Data
• Trigger IN: TTL, input impedance.............................................................................................. 1kΩ
• Trigger OUT: TTL, output impedance .......................................................................................50Ω
The EMAT Detector Morning Dew provides a means for NDT inspectors to benefit from the advantages of non-contact EMAT transducers for pulse-echo flaw detection and thickness gauging, without the large capital outlay of replacing existing piezoelectric based flaw inspection systems and thickness/corrosion monitors. • Acts as a bridge between an EMAT probe and a flaw detector designed for piezoelectric transducers. • Incorporates low power averaging electronics such that the signal-to noise performance of the EMAT measurement is dramatically improved. • Features automatic gain control (AGC), which increases reliability and inspection speed and can eliminate the need for operators to keep adjusting an EMAT stand-off ring or the gain setting on the flaw detector. Designed to work with modern NDT inspection systems, The EMAT Detector Morning Dew, when used with a suitable EMAT (provided as part of the package), has sufficient signal strength and resolving power to work on both oxide coated and oxide free ferritic steel surfaces, providing a major advantage for plant inspection over alternative systems. In certain circumstances measurement of austenitic stainless steel is also possible. The adapter can also be used with piezoelectric transducers for some situations where the signal-to-noise ratio is too poor to allow measurement, but averaging is able to reveal the ultrasonic signals.
As most flaw detectors have a pulse repetition rate significantly greater than the screen update rate, most of the potential data available with a standard flaw detector is lost. There are many flaw detectors that do not posses either an averaging capability or an automatic gain control feature. In such situations the Morning Dew can enable your flaw detector to perform EMAT measurements that were previously not possible. By way of an example, consider the images taken from a flaw detector shown overleaf using a shear wave EMAT on a stainless steel sample with a high gain low noise EMAT preamplifier with and without the averaging feature.
Multi-Channel EMAT System The Electro-Magnetic Acoustic Transducer (EMAT) System is a computer controlled multichannel electronic system to operate EMAT transducers for couplant-free transmitting and receiving of oblique incident bulk ultrasonic waves and guided waves in ferromagnetic materials. The system serves as signal-generating and processing component. It provides timedelayed RF signals for transmitter stages, amplification, filtering and summation of the received signals and the power supply for the transducer electromagnets. The control of the system, such as frequency, beam angle, pulse length (number of cycles), pulse repetition rate, transducer selection, etc., is performed by the system setup program.