ISO 6551:1982

Overview

ISO 6551:1982 - "Petroleum liquids and gases - Fidelity and security of dynamic measurement - Cabled transmission of electric and/or electronic pulsed data" provides guidelines to preserve the integrity of pulsed, cabled data used in fluid metering systems. It focuses on ensuring the primary indication (the final reference reading used for transactions such as custody transfer, fiscal accounting and royalty measurement) remains credible against functional failures and external disturbances. The Standard addresses design, installation, use and maintenance criteria for pulse transmission systems while noting that regulatory and detailed safety requirements are not fully covered.

Key topics and requirements

• Levels of security (E → A): Five security levels are defined (Level E = minimum acceptable; Level A = highest). Each level prescribes progressively stronger monitoring, redundancy and error-handling measures (examples include manual checks, dual-channel comparison, continuous monitoring and automatic correction).
• Primary vs secondary indication: Definitions and guidance on maintaining the integrity of the primary indication (transducer, cabling, signal conditioning, processing/scaling and indicator) and the role of auxiliary/secondary readouts.
• Pulse transmission components: Requirements for pulse transmitters, preamplifiers, signal conditioning (pulse shaping, limiting, common-mode rejection), totalizers and scalers.
• Noise and transients: Identification of disturbances - transients (≤ 0.2 s) and longer noise - and measures to mitigate their effects on fidelity.
• Redundancy and comparison methods: Use of alternate transmission lines, dual-channel systems, comparators/analysers to detect frequency/phase/sequence differences, and backup power provisions.
• Error monitoring and alarms: Recommendations on automatic and manual error monitoring intervals, alarm signalling and corrective actions.
• Scope limits and safety notes: Clarifies that conforming to ISO 6551:1982 does not increase inherent measurement precision and does not replace legal metrology, safety rules or ship classification requirements.

Applications

• Revenue and custody transfer metering for petroleum liquids and gases
• Meter proving and pipeline metering systems
• Offshore and marine installations (used with ship classification and safety rules)
• Flowmeter and pulse-transmission equipment manufacturers, system integrators and metrology service providers

Who should use this standard

• Meter manufacturers designing pulsed output and transmission systems
• Operators and owners of custody transfer and fiscal metering installations
• System integrators implementing redundant or secure cabled pulse systems
• Calibration and testing labs establishing verification and monitoring procedures
• Regulatory and inspection bodies as a reference for good practice (alongside legal metrology rules)

Related guidance

ISO 6551:1982 is intended to be used together with national legal metrology requirements and relevant safety codes (including ship classification society rules for marine applications). It complements broader metering and measurement standards by addressing fidelity and security for cabled pulsed data in petroleum applications.