Modern Approach to Instrumentation Maintenance: Work Smarter, Not Harder

The Problem: Outdated Maintenance Practices

Many industrial facilities continue to spend thousands of labor hours performing annual calibrations on smart instruments that drift as little as 0.025% per year.

This 'annual approach to calibration frequency was developed for older analog (non-Smart) instrumentation technology that drifted up to 50x quicker than today's Smart transmitters and fails to leverage the advances in modern smart transmitters. For more on this issue, see our blog on I&C calibration frequency mistakes.

"Many I&C groups still use the same basic maintenance plans and procedures that they were using back when Gilligan's Island was airing new shows..."

A Simple, High-Value Solution

Instead of relying solely on traditional 'annual' calibrations to find and resolve instrument problems, implement more frequent 1-minute walk-by checks that typically:

• Require no process interruption
• Require no permits
• Require no bypasses or overrides
• Require no disconnecting or connecting of electronics, wires, or components
• Require no connection of test equipment, pressure pumps, etc.
• Require no valve lineups or system manipulations

But which would provide the following benefits:

• Provide early detection of the most likely problems
• Provide coverage of a much wider range of potential failures than a simple transmitter calibration alone
• Substantially increase reliability
• Optimize maintenance resources

The 60-Second Walk-By Inspection

This simple, non-intrusive procedure consists of:

1. Visual inspection of the instrument for physical damage, condensation, or environmental issues (see our blog on recommended instrument inspection checks as a guide)
2. Check transmitter display for any alerts, warnings, or error messages
3. Compare transmitter PV (Process Variable) reading to controller/HMI data (within 1% tolerance) - easily done via radio chat with operator.
4. Cross-check against secondary instruments when available (process safety vs. process control transmitters offer the best comparisons, but mechanical gauges can be an option for gross error identification, but gauge tolerance must be factored into the acceptable tolerance).

Why This Approach Works: The Evolution of Instrumentation

Today's smart transmitters differ significantly from the instruments that shaped most maintenance programs. Here are some of the differences of today's isntrumentation: 

• 10-40× more stable with drift rates often below 0.025% annually (compared to as much as 1% per year in the 80's & 90's for non-smart instruments)
• Built-in diagnostics that can actively detect and report many problems (if we are paying attention)
• Integrated displays showing PV values, diagnostics alerts & warnings, and more.
• Significantly lower failure rates due to improved design and electronics

In legacy systems, transmitters were often the weakest link in the measurement loop, and transmitters typically drifted by about 0.5% to 1% per year! It is for that reason, that the 'annual calibration check' constituted the primary workload of most instrument technicians and why it was the biggest bang for the buck for improving reliability and performance of plant instrumentation. But with modern smart transmitters (which make up the vast majority of currently installed industrial instrumentation), this is no longer the case. Plant maintenance plans should strategically factor in these advances in a strategic and purposeful way, instead of blindly carrying forward maintenance plans from a time when Gilligan's Island was airing new episodes and instrumentation was quiet primitive and limited. 

To give an example of the kinds of improvements in today's instrumentation, the new premium class of Rosemount 4088 multivariable flow transmitter has a 12-year stability guarantee and those aren't just lofty 'claims' - they are 3-sigma statistical performance, meaning 99.7 of transmitters achieve those results... Other vendors likely have similar offerings now days, but I'm most familiar with the blue brand. 

The Mistakes & Misconceptions

So - why exactly are so many sites still performing thousands of hours of annual calibrations on all transmitters like they needed to back in 1980? In most cases, the reason is simply that nobody with the combination of knowledge and influence has taken the time to look at the details and do the hard work of making change happen. 

And the worst part, is that all those excessively frequent 'recalibration procedures' are likely doing more harm than good, because of the following:

1) The modern field transmitters are typically 4-10 times MORE 'accurate' than the field calibration equipment being used to test and calibrate them. 

So that 'perfectionist' technician who adjusts the calibration even when it's only off by 0.1% - is actually just transferring the bigger error of the calibration equipment into the field transmitter... Go compare the specs per the official references - it's enlightening and contrary to what most people assume. 

2) The likelihood of a mistakes; likelihood of misconfigurations or unintentional / misunderstood changes or adjustments; valve lineup mistakes, etc..

3) The physical wear and tear on seals, housings, terminals, ferrules, crimps, and wiring; etc..

Strategic Implementation Notes

While "walk-by inspections" provide excellent value, the overall comprehensive maintenance plan should still include:

1. Periodic sensor verification based on specific drift and failure profiles (though in many cases this can be extended dramatically beyond current periodicities). 
2. Occasional full calibration checks / verifications are still needed at some periodicity (though possibly every 3-5 years vs every 6-12 months in many cases. But when doing those 'intrusive' calibration check procedures, the techs have an opportunity to gather other very useful information and data that walk-by inspections don't cover, such as:
   • Configuration verification (Tag/ID, URV/LRV, damping, signal processing)
   • Review of logged alerts/warnings
   • Impulse line operational verification (for applicable instruments)
   • Specialized tests for level, flow, and analytical measurements

Business Impact

Implementing these changes can:

• Significantly reduce maintenance costs by optimizing labor hours. Many shops spend roughly 1/4 or more of their labor hours doing excessively frequent calibrations. 
• Free up technicians to perform higher-value work such as solving plant problems and performing more preventative maintenance. 
• Improve process reliability and safety through earlier detection of issues and by finding more of the potential problems than with 'calibration checks' alone.
• Extend effective calibration intervals based on actual performance data - See our blog on calibration frequency mistakes and guidance for more

Next Steps

To optimize your instrumentation maintenance program:

1. Review your current smart transmitter inventory
2. Review the reference manual guidance on required periodicity of maintenance and maintenance suggestions. 
3. Develop walk-by inspection checklists to ensure consistency of inspections and checks. 
4. Implement a mixed-strategy approach of walk-by checks and calibration / verification checks based on criticality
5. Train your personnel on the changes and implementation so they understand the why's and the how's and buy into them.
6. Track and measure performance improvements

Exceptions and Caveats 

1. Many regulatory requirements are still based on the older standards and even if they are outdated, you must still follow any regulatory requirements. 
   1. In some cases, if you can prove reasoning with reference manuals, specs, and details, regulatory agencies will allow exceptions and modification to procedures or practices (including calibration frequencies, etc.). 
2. Even though a plant with a standard 0.5% of span error tolerance may calculate out an 8 to 10-year frequency for many common transmitters, that does not mean that some of those instruments shouldn't be calibration checked more frequently. This comes down to an engineering judgment and should be treated like any other engineering decision (gather the info, collect the stats, do the math, and then factor in human knowledge and experience - then test and adjust based on findings). 
3. This is meant to be a condensed article to convey the idea of doing more frequent, but easier and less intrusive maintenance checks that leverage the advantages of all those pretty (expensive) transmitters that are already installed in nearly all industrial plants. The details can vary by site and system and must be studied and factored into any good engineering or maintenance program.  

Training is Key

Getting technicians and engineers to become aware of the technologies and related issues and training them on the often-missed details of modern instrumentation is the first step to making improvements and preventing mistakes or problems from being carried forward due to tribal knowledge or other reasons. 

Our training courses strive to help students understand the details of I&C systems that seem to be missed by most of the theory textbooks and courses and that aren't spelled out in vendor literature, so personnel can understand the common problems and issues in the field. 

Want to learn more about boosting your team or optimizing your I&C maintenance program? Contact me for a consultation or visit my website for additional resources.