Introduction
GB/T 18659-2002, identical to ISO 9104:1991, specifies methods for evaluating the performance of electromagnetic flowmeters (EMFs) for conductive liquid flow in closed pipes. It provides unified evaluation criteria for manufacturers, users, and third-party testing bodies, crucial for measurement accuracy and reliability.
Scope
The standard applies to EMFs with integral or remote sensors and converters. Liquid conductivity is typically ≥5 μS/cm; lower conductivity requires technical agreements. It does not cover open-channel or insertion flowmeters.
Referenced Standards
- GB/T 17614.1-1998 Transmitters for industrial process control systems – Part 1: Methods for performance evaluation
- JB/T 9248-1999 Electromagnetic flowmeters
Terms and Definitions
- Intrinsic error: Difference between indicated value and true value under reference conditions.
- Repeatability: Consistency of indications under same conditions.
- Reference conditions: Standard environmental, power, and fluid conditions for testing.
- Maximum flow rate: Upper limit for normal operation.
- Rangeability: Ratio of maximum to minimum flow rate.
Performance Indicators
| Indicator | Requirement |
|---|---|
| Intrinsic error limit | Class 0.5: ±0.5%; Class 1.0: ±1.0%; Class 1.5: ±1.5%; Class 2.5: ±2.5% |
| Repeatability | ≤ 1/3 of absolute intrinsic error limit |
| Stability | Error change ≤ 1/2 of limit after 7 days continuous operation |
| Ambient temperature effect | Output change ≤ 1/2 of limit per 10°C change |
| Power supply effect | Output change ≤ 1/2 of limit for ±10% voltage variation |
Test Methods
Static volumetric or master meter methods are used. Test facility uncertainty must be ≤ 1/3 of the EMF's intrinsic error limit. Conditions: 20±5°C, 45%-75% RH, stable power and fluid temperature. At least 5 flow points are tested, including forward/reverse runs.
Inspection Rules
Type inspection covers all performance items every two years or after design changes. Routine inspection includes intrinsic error, repeatability, insulation resistance, and dielectric strength.
Marking, Packaging, and Storage
Product marking includes model, accuracy class, manufacturer, serial number. Packaging protects against moisture and shock. Storage at -40~+70°C, ≤85% RH, no corrosive gases.
Application Recommendations
SIENCUN (Xiechuang Instrument) EMFs comply fully with GB/T 18659-2002. Users should select proper size and lining based on conductivity, temperature, pressure, and flow range. Ensure straight pipe runs (5D upstream, 3D downstream). Regular calibration maintains long-term stability.
Conclusion
GB/T 18659-2002 provides a scientific basis for EMF performance evaluation, essential for measurement quality. Understanding the standard aids correct selection, installation, and maintenance, enhancing process control accuracy and efficiency.