Through-Transmission Technique
Through-transmission is an ultrasonic test where a transmitter and a receiver are placed on opposite sides of the test piece to detect internal defects by intensity attenuation. It is often used to detect cracks or voids in metals.
Physical-Chemical Mechanism of Action
An ultrasonic wave packet is emitted by a transmitter and propagates through the test piece. When the sound is reflected or absorbed at a defect (e.g., a crack), the intensity of the received signal changes. The receiver measures these changes and provides a signal display.
Metallurgical Relevance & Risks in Welding
Through-transmission is especially important in inspecting weld quality, as it can detect microscopic cracks or incomplete fusion. Incorrect settings or poor contact between transmitter and receiver can lead to missed detections, posing risks to component safety.
Workshop Practice & Instructions
• Transmitter-Receiver Distance: The two devices must be placed so they form a straight line and can cover the maximum sound path of the test piece. A distance of at least 10 cm is typical.
• Sound Frequency: Depending on the material and type of defect, a specific frequency is chosen. For metals with high body content (e.g., steel), frequencies between 2.5 MHz and 10 MHz are used.
• Calibration: Before each test, the equipment must be calibrated to ensure accurate measurements. This includes setting the receiver to the correct threshold.