Overview
ISO 20456:2017 - Measurement of fluid flow in closed conduits - provides practical guidance for the selection, installation, calibration and verification of electromagnetic flowmeters used to measure the flowrate of conductive liquids in fully filled pipes. The standard covers industrial electromagnetic meters using either alternating current (AC) or pulsed direct current (DC) excitation, and applies to instruments powered from mains, batteries or other supplies. It explicitly excludes insertion-type meters, partially filled pipes or open channels, magnetically permeable slurries, liquid metal applications and does not specify safety requirements for hazardous environments.
Key topics and technical requirements
ISO 20456:2017 focuses on topics that affect meter performance and measurement uncertainty:
- Theory and basic formulae - fundamental principles behind electromagnetic flow measurement and relevant symbols.
- Construction and principle of operation - sensor (meter tube, electrodes, electromagnet) and transmitter design, including AC and pulsed‑DC excitation methods.
- Flowmeter outputs and reference signals - how flow voltage is generated and processed by the transmitter.
- Equipment marking and recommended data - information that should accompany sensors and transmitters.
- Installation design and good practice - sizing, mounting conditions, electrical connections, potential equalization, flanged dimensions and transmitter siting to achieve optimal accuracy.
- Operational considerations - effects of liquid conductivity, Reynolds number, velocity profile and other field conditions.
- Calibration, in‑situ verification and validation - guidance on laboratory calibration, on-site electronic verification and validation runs.
- Performance evaluation and uncertainty analysis - methods to assess meter performance and quantify measurement uncertainty.
- Informative annexes - materials for sensor construction, AC/DC practical considerations, cathodic protection, unit conversions and manufacturers’ accuracy specifications.
Practical applications
ISO 20456:2017 is practical for industries that rely on accurate volumetric flow measurement of conductive liquids in closed pipes, such as:
- Water and wastewater treatment
- Chemical and petrochemical processes (non‑magnetic slurries)
- Food and beverage processing
- Pulp and paper, and general process industries
The guidance helps ensure reliable metering in custody transfer, process control, leak detection, and mass balance calculations.
Who should use this standard
- Flowmeter manufacturers and designers (sensor and transmitter specifications)
- Plant engineers and instrumentation designers (installation and electrical grounding)
- Calibration laboratories and testing houses (calibration, validation, uncertainty assessment)
- Asset owners and operators seeking best practice for electromagnetic flowmeter deployment
Related standards
ISO 20456:2017 replaces and consolidates earlier ISO documents (ISO 6817, ISO 9104, ISO 13359) and complements other flow measurement and calibration standards; consult relevant ISO/IEC and industry standards for safety and hazardous‑area requirements.
Open preview (PDF)Measurement of fluid flow in closed conduits — Guidance for the use of electromagnetic flowmeters for conductive liquids
