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IEC 62828-3:2018 – Reference Conditions and Procedures for Testing Temperature Transmitters
🌡️ IEC 62828-3 replaces the legacy IEC 60770 series for temperature transmitters and harmonizes with IEC 61298. It provides the first dedicated standard with specific test procedures for temperature transmitters.
⚠️ When the transmitter is separate from the sensing element (RTD, TC, etc.), this standard applies only to the transmitter. For fully integrated devices, the complete unit is tested as one system.
1. Scope and Reference Conditions
IEC 62828-3:2018 establishes specific procedures for testing temperature transmitters used in industrial process measurement and control systems. It covers transmitters for resistance temperature detectors (RTDs) per IEC 60751 and thermocouples (TCs) per IEC 60584. Reference test conditions include ambient temperature (23 degrees C +/- 2 K), relative humidity (45% to 75%), and atmospheric pressure (86 kPa to 106 kPa).
Part 3 is part of the broader IEC 62828 series, which reorganizes and modernizes the legacy IEC 60770 and IEC 61298 standards. Part 1 provides general procedures for all transmitter types, while Parts 2-5 cover pressure, temperature, level, and flow transmitters respectively.
2. Test Procedures and Accuracy Verification
Clause 6 details test procedures under standard and operating reference conditions. Key tests include: accuracy verification at reference conditions, influence of ambient temperature variation, influence of supply voltage variation, warm-up drift characteristics, and long-term stability.
Accuracy verification (Clause 6.2.2) requires measuring transmitter output at a minimum of 5 equally spaced points across the measurement span. The measured error is compared against the manufacturer’s specified accuracy class. For temperature transmitters, precision resistance decades simulate RTD inputs and precision voltage sources simulate thermocouple inputs.
3. Engineering Insights for Calibration and Documentation
Clause 7.2 introduces ‘Total Probable Error’ (TPE), combining individual uncertainties from reference measurement, calibration chain, ambient influences, and long-term drift. Engineers compute TPE as the root-sum-square of all contributing components. For a typical 4-20 mA transmitter with 0.1% accuracy, the TPE budget includes reference standard uncertainty (0.02%), calibration chain (0.03%), temperature influence (0.05%), and long-term drift (0.04%), yielding a combined TPE of approximately 0.07%.
Annex A provides guidance on documentation requirements. Manufacturers should declare: measurement range, output signal type, supply voltage range, reference accuracy, temperature coefficient, response time, and long-term stability following the modular structure of IEC 62828-1.
Temperature Transmitter Test Parameters
| Test Parameter | Reference Condition | Test Method | Acceptance Criteria |
|---|---|---|---|
| Reference accuracy | 23 degrees C +/- 2 K | 5-point calibration check | Within specified class (e.g., 0.1%) |
| Ambient temperature effect | -40 to +85 degrees C | Temperature chamber test | <=0.01%/K of span |
| Supply voltage effect | 10-36 V DC | Voltage variation test | <=0.005%/V of span |
| Warm-up drift | 30 min stabilization | Continuous monitoring | <=0.05% of span |
| Long-term stability | 1 year | Annual calibration check | <=0.1% of span per year |
Frequently Asked Questions
Q1: What is the difference between IEC 62828-3 and the older IEC 60770 series?
IEC 62828-3 modernizes and consolidates test procedures previously spread across multiple documents, providing a systematic standard suite with consistent terminology and test methods. When IEC 62828 is published, IEC 60770 is withdrawn.
Q2: Does the standard cover testing with actual RTD/TC sensors?
No. When the transmitter is separate from the sensing element, the standard applies only to the transmitter. Testing uses simulated sensor signals from precision resistance decades (RTD) or precision voltage sources (TC). Only fully integrated devices are tested as complete units.
Q3: How is Total Probable Error calculated?
TPE combines all uncertainty components using root-sum-square method. Components include reference uncertainty, calibration chain errors, ambient influence, and drift. It gives engineers a realistic estimate of measurement uncertainty in actual operating conditions.
