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IEC TS 62492-2:2013 — Radiation Thermometers — Determination of Technical Data
Industrial process control devices — Radiation thermometers — Part 2: Determination of the technical data for radiation thermometers
Why Standardization Matters
Without standardized technical data, users cannot reliably compare radiation thermometers from different manufacturers for a given application. This standard ensures that published specifications are obtained under consistent, reproducible conditions.
Without standardized technical data, users cannot reliably compare radiation thermometers from different manufacturers for a given application. This standard ensures that published specifications are obtained under consistent, reproducible conditions.
NETD Design Consideration
NETD is fundamentally limited by the signal-to-noise ratio of the detector and optics. For low-temperature applications (below 100 C), a higher NETD directly translates to reduced temperature resolution. Designers should specify NETD at the lowest expected target temperature.
NETD is fundamentally limited by the signal-to-noise ratio of the detector and optics. For low-temperature applications (below 100 C), a higher NETD directly translates to reduced temperature resolution. Designers should specify NETD at the lowest expected target temperature.
Engineering Insight
When selecting a radiation thermometer for a critical control application, the most often overlooked parameter is the size-of-source effect. For measurements on targets smaller than the optical field-of-view, SSE can introduce errors of several degrees that are not captured by the basic accuracy specification.
When selecting a radiation thermometer for a critical control application, the most often overlooked parameter is the size-of-source effect. For measurements on targets smaller than the optical field-of-view, SSE can introduce errors of several degrees that are not captured by the basic accuracy specification.
Scope and Importance of Standardized Technical Data
Radiation thermometers (also known as infrared thermometers or pyrometers) are widely used in industrial process control for non-contact temperature measurement. However, the comparability of instruments from different manufacturers has historically been hindered by inconsistent methods for specifying technical data. IEC TS 62492-2, published in 2013 as a Technical Specification, addresses this gap by defining standardized test methods for determining the technical data of radiation thermometers used in industrial process control.
The standard covers a comprehensive set of performance parameters including: measuring temperature range, measurement uncertainty, noise equivalent temperature difference (NETD), measuring distance, field-of-view (target size), distance ratio, size-of-source effect (SSE), emissivity setting accuracy, spectral range, influence of ambient temperature, influence of humidity, and long-term stability.
Key Performance Parameters and Test Methods
The standard defines the measurement temperature range as the range within which the instrument meets all specified accuracy requirements. The test method involves comparing the radiation thermometer reading against a reference blackbody source at multiple temperature points across the claimed range. Measurement uncertainty must be expressed with a coverage factor (k=2) corresponding to approximately 95% confidence level.
Noise Equivalent Temperature Difference (NETD) is a critical parameter for low-temperature measurements and is determined by measuring the standard deviation of output readings when viewing a stable temperature source. The field-of-view is characterized as a function of measuring distance. The Size-of-Source Effect (SSE) quantifies how the reading changes when a source larger than the nominal target fills the field of view — a particularly important parameter for small target measurements.
Environmental Influences and Long-Term Stability
The standard addresses how ambient temperature changes affect the radiation thermometer reading — a critical consideration for instruments used in outdoor or uncontrolled environments. The test method involves placing the instrument in a temperature chamber and varying the ambient temperature while measuring a stable blackbody source. Similarly, the influence of air humidity is evaluated.
Long-term stability testing involves repeated measurements over an extended period (typically 3 to 12 months) to establish drift characteristics. The standard requires that the drift be quantified and included in the measurement uncertainty budget for applications requiring long-term accuracy. The spectral range determination involves measuring the instrument relative spectral response using a monochromator or FTIR spectrometer.
| Parameter | Symbol | Typical Test Method | Key Influence |
|---|---|---|---|
| Measurement uncertainty | U (k=2) | Blackbody comparison | Overall accuracy |
| Noise equiv. temp. difference | NETD | Std. dev. of stable target | Low-temp resolution |
| Size-of-source effect | SSE | Variable aperture | Small target error |
| Distance ratio | D:S | Spot size vs. distance | Working distance limit |
| Long-term stability | Drift | 3-12 month repeatability | Calibration interval |
Frequently Asked Questions
Q: What is NETD and why is it important?
NETD (Noise Equivalent Temperature Difference) represents the smallest temperature difference that can be resolved above the noise floor. Lower NETD values indicate better temperature resolution, which is critical for applications requiring fine temperature discrimination.
Q: What is the Size-of-Source Effect (SSE)?
SSE quantifies how the temperature reading changes when the target source is larger than the specified measurement spot. It arises from optical scattering and diffraction within the thermometer. SSE can cause significant errors when measuring small targets.
Q: How should measurement uncertainty be reported per this standard?
Measurement uncertainty should be reported with a coverage factor k=2 (approximately 95% confidence level). The uncertainty budget should include contributions from the blackbody reference, the radiation thermometer under test, and environmental factors.
Q: Why is this a Technical Specification (TS) rather than a full International Standard?
The subject was still under technical development at the time of publication, and there was not yet sufficient consensus for a full International Standard. TS status allows for revision within three years.
