ULTRA VIOLET METER (UV METER) – FULL DESCRIPTION
A UV Meter (also called Ultraviolet Radiometer) is a precision measuring instrument used to measure the intensity of ultraviolet radiation, usually in the UV-A spectrum (365 nm). It ensures that UV light sources such as black lights used in Magnetic Particle Inspection (MPI) and Fluorescent Penetrant Inspection (FPI) provide the required UV intensity for proper flaw visibility.
Purpose of a UV Meter
A UV meter is used to:
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Measure UV-A intensity (µW/cm² or W/m²)
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Verify UV lamp performance and stability
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Ensure compliance with standards like ASTM E1444, ASTM E1417, ISO 3059
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Maintain inspection quality for fluorescent MPI/FPI
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Detect lamp degradation or filter damage
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Calibrate and document UV exposure conditions
✔ Working Principle
A UV meter consists of:
1. UV Sensor / Detector
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Sensitive to UV-A spectrum (approx. 320–400 nm)
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Peak calibration typically at 365 nm
2. Optical Filter
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Allows only UV-A wavelength to reach the sensor
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Blocks visible and infrared light
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Ensures accurate measurement in NDT environments
3. Digital or Analog Display
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Shows real-time UV intensity
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Units: µW/cm² or mW/cm²
4. Electronic Circuitry
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Converts sensor output into readable intensity values
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Includes auto-ranging and temperature compensation
✔ Types of UV Meters
1. Digital UV Meter
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High accuracy
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Graphical or numeric display
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Data logging capability
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USB/Bluetooth options
2. Analog UV Meter
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Needle indicator
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Simple design
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Suitable for basic field checks
3. Integrated UV-IR Combo Meters
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Measures both UV and visible light
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Used in high-accuracy laboratories
✔ Technical Specifications (Typical)
| Parameter | Typical Value |
|---|---|
| Wavelength Range | 320–400 nm |
| Peak Sensitivity | 365 nm |
| Measuring Range | 0–5,000 µW/cm² or 0–20 mW/cm² |
| Accuracy | ±5–10% |
| Sensor Type | Silicon photodiode with UV filter |
| Display | Digital/Analog |
| Battery Life | 100–200 hours |
| Calibration Period | Every 12 months |
✔ How to Use a UV Meter
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Switch on the UV light source (black light).
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Allow lamp to stabilize for 5 minutes.
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Place the sensor of the UV meter perpendicular to the lamp at 15 inches (38 cm) distance.
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Record the intensity reading.
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Compare with standard requirements:
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Minimum UV-A intensity for MPI/FPI: 1000 µW/cm² at 15 inches
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Document the values as per inspection procedure.
✔ Common Applications
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Fluorescent Magnetic Particle Inspection (MPI)
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Fluorescent Penetrant Inspection (FPI)
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UV light calibration and maintenance
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Quality assurance in aerospace and automotive industries
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Testing darkroom compliance
✔ Benefits
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Ensures code compliance
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Improves flaw detection accuracy
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Detects faulty or weakening UV lamps
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Ensures consistent inspection quality
✔ Limitations
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Sensor needs regular calibration
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Sensitive to dust and fingerprints
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Must be used in darkened environments for accurate measurement
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Can degrade over time due to UV exposure
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