Old ISA-RP55.1 Standards

Obsolete - but stubbornly persistent

One of several outdated details of the old ISA-RP55.1 standard that seems to persist in most industries is the calibration frequency guidance. 

Often on LinkedIn and other social media sites or even with various AI tools (or the posts created with them) I see references to information that is grossly outdated and which has been carried forward from way back when many companies actually had training and development programs. Very little training has been provided to personnel on the changes in instrumentation over the years, and the gaps and weaknesses show it. 

The actual standard that these assumptions come from was published in 1975. That is literally half of a century ago! BUT... people still speak of the annual calibration requirement as if it were new. 

Back in 1975, instruments used very crude analog electronics (or worse) which had extremely high drift rates of up to 1% per year or more. In order to keep those drifty instruments within a reasonable tolerance, the general guidance was to check/calibrate them every year. 

But things have changed... as discussed in some of my other posts, today's transmitters have up to 40 times slower drift rates than the instruments that this old standard was based upon.

SO... two new standards have been published to help provide more relevant guidance for modern equipment. 

ISA-RP105.00.01 (2018) - Management of Instrumentation & Calibration and Maintenance Programs

ISA-TR52.00.02 (2020) - Supplemental Information on the Calibration of Industrial Process Instruments

Here are some of the highlights of these standards:

ISA-RP105.00.01

Focus and Scope:

• Provides a comprehensive framework for managing instrumentation calibration programs
• Addresses the management systems and processes rather than specific technical procedures
• Applies to all types of process measurement and control instrumentation

Key Content Relevant to Blog:

• Evidence-Based Intervals: Explicitly recommends abandoning arbitrary calendar-based schedules in favor of statistically determined intervals based on performance history
• Risk-Based Approach: Introduces methodologies for prioritizing instrumentation maintenance based on process criticality, reliability history, and consequence of failure
• Documentation Requirements: Establishes comprehensive as-found/as-left documentation as the foundation for continuous improvement
• Decision Framework: Provides a structured approach to determining which instruments require calibration, when they should be calibrated, and how the calibration should be performed
• Technology Considerations: Acknowledges fundamental differences in maintenance requirements between analog, smart, and fieldbus/digital instrumentation

Notable Quotes:

• "Calendar-based scheduling should be used only when there is no performance history available or when there are specific regulatory requirements"
• "The goal of instrumentation maintenance is reliable performance, not compliance with arbitrary schedules"
• "Documentation is not just for record-keeping but serves as the foundation for continuous improvement of the calibration program"

ISA-TR52.00.02

Focus and Scope:

• Technical report providing detailed guidance on calibration practices for industrial instrumentation
• Complements ISA-RP105.00.01 by focusing on technical aspects rather than program management
• Addresses both traditional and modern digital instrumentation technologies

Key Content Relevant to Blog:

• Test Uncertainty Ratios: Challenges the traditional "4:1 rule" and provides guidance on appropriate TURs for modern instrumentation
• Uncertainty Analysis: Offers detailed methodologies for comprehensive measurement uncertainty calculations
• Smart Instrument Considerations: Addresses the unique characteristics of smart and digital instruments, including their significantly lower drift rates
• Whole-System Verification: Emphasizes the importance of verifying the entire measurement chain, not just the transmitter
• Calibration Procedures: Provides guidance on proper calibration procedures that minimize technician-induced errors

Notable Technical Information:

• Presents data showing that modern smart transmitters typically exhibit drift rates 5-10 times lower than their analog predecessors
• Acknowledges that TURs of 1:1 or even less may be acceptable when supported by proper uncertainty analysis
• Documents that up to 70% of measurement problems originate in primary elements or installation issues rather than transmitter calibration
• Provides statistical methods for analyzing as-found/as-left data to determine optimal calibration intervals 

Every instrument technician, engineer, student, instructor, blogger, or enthusiast should really take a close look at these standards and likely get a marker out to sketch up their old textbooks from college (even pretty new textbooks sadly). 

So... The answer to the question (on social media post) of whether instrument calibrations are required annually by ISA standards is decisively FALSE. Yes, that WAS true from 1975 until 2018 with ISA-RP55.1 - but has long since been updated by newer standards that account for the changes in modern equipment over the last several decades.