As per IS 13311 (Part 1), the natural frequency of transducers for a path length of more than 1500 mm is:
Correct Answer: C. Greater than or equal to 20 kHz
📚 Detailed Explanation: Transducer Frequency for UPV Test (IS 13311 Part 1)
Why C (≥20 kHz) is correct: The Ultrasonic Pulse Velocity (UPV) test is a non-destructive method to assess concrete quality. IS 13311 (Part 1) specifies the transducer frequency based on path length. For longer paths (>1500 mm), a lower frequency (≥20 kHz) is used because higher frequencies attenuate more rapidly over distance.
IS 13311 (Part 1): Transducer Frequency vs. Path Length
| Path Length (mm) | Natural Frequency of Transducer | Min. Transverse Dimension (mm) |
|---|---|---|
| Up to 500 | ≥150 kHz | 25 |
| 500–700 | ≥60 kHz | 70 |
| 700–1500 | ≥40 kHz | 150 |
| >1500 | ≥20 kHz | 300 |
Why Lower Frequency for Longer Paths?
Ultrasonic waves experience attenuation (energy loss) as they travel through concrete. High-frequency waves have shorter wavelengths and scatter more at aggregate boundaries, resulting in greater energy loss per unit distance. For long paths, a lower frequency is therefore used to ensure the pulse is detectable at the receiving transducer.
UPV Quality Assessment (IS 13311)
| Pulse Velocity (km/s) | Concrete Quality |
|---|---|
| >4.5 | Excellent |
| 3.5–4.5 | Good |
| 3.0–3.5 | Medium / Doubtful |
| <3.0 | Poor |
- For path lengths >1500 mm: transducer frequency ≥20 kHz.
- Inverse relationship: longer path → lower frequency to minimize attenuation.
- UPV test assesses concrete homogeneity, detect cracks, and estimate strength (non-destructively).