Behind every plant process among the heavy industries, there lies a lineup of instrumentation that can set production up for success, or strip away any shot of high-quality output. Calibration, the act of comparing plant instrumentation with a known standard, is a maintenance tool—and often a regulatory requirement—holding these instruments in line.
Though calibration is critical for accurate, efficient, and safe production, it can be time-consuming and costly, resulting in downtime or incidents. To determine the best balance for plant efficiency and process safety, it is critical to determine just how accurate each instrument must be, and how frequently it must be calibrated.
Accuracy requirements are often linked to calibration frequency, so evaluators must carefully consider both these factors. More frequent calibrations than necessary waste resources and increase planned downtime, while too few adversely impact product quality, regulatory compliance, and safety, while increasing the likelihood of unplanned downtime.
Determining calibration frequency – where to start
The first step for framing accuracy requirements is to perform a plantwide instrumentation assessment. Start by identifying all equipment parts and instrument-related systems. Once this is complete, plant personnel need to define each instrument’s criticality along three effects: to the end product, the process operations, and protecting workers, the environment, and production assets.
Based on this criticality assessment and the consequences of instrumentation inaccuracy, evaluators should assign a maximum permissible error (MPE) to each device. The MPE, combined with regulatory requirements, can be used to determine calibration frequency and procedures.
Instruments with a high MPE must often be lab tested in stringent conditions, but evaluators can frequently make the case for less disruptive calibration methods—or even inline verification—for instrumentation with a lower MPE.
Utilizing inline verification to extend calibration services
Verification is a way to ensure proper instrumentation operation without removing it from the process for a complete calibration. While calibration directly compares the accuracy of an instrument against a reference, verification is qualitative in nature, using intrinsic or external sensor tools to perform health checks to confirm the instrument is functioning as intended.
Inline verification improves plant availability because there is no need to remove the instrument from the process for calibration, eliminating the risk of damage during removal and transit, and the potential for mistakes during reinstallation. Additionally, verification empowers operators to track an instrument’s performance over time, which provides early notice of measurement drift, reducing unscheduled downtime.
Many of Endress+Hauser’s smart instruments continuously check their own health using Heartbeat Technology, providing significant reliability and safety advantages over instruments without this functionality. These smart instruments automatically store their self-diagnostic records internally, and this data is easily readable via HART, WirelessHART, Bluetooth, and other methods of communication between the instrument and a host, such as asset management system or a distributed control system.
Often, inline verification can greatly extend industry-required intervals between intrusive calibration, yielding more production time. Additionally, verification provides increased measurement confidence and advance warning of instrument failure, empowering plants to operate more reliably and efficiently.
Determining calibration methods
Some level of calibration is necessary in every industry, but there are many procedural options available, providing opportunities to select the least disruptive methods to plant operations.
Most plants cannot perform calibrations on all sensor types, for example flowmeters, which are far more complicated to calibrate than temperature or pressure sensors. Many plants in the heavy industries may choose to calibrate temperature and pressure instruments on site, and then send their flowmeters to a lab for calibration.
Additionally, plants may decide to call in accredited calibration providers, who can calibrate flowmeters and numerous other measuring devices at a plant with a mobile calibration rig. Onsite instrumentation calibration offers many benefits:
- Improves plant availability
- Provides visibility to error sources
- Minimizes requirements for additional inventory and spare parts because calibrated instruments are out of and back in service very quickly
- Alleviates the need to disassemble and ship devices contaminated by process fluids, while eliminating costly decontamination measures
Endress+Hauser maintains a network of high-end regional calibration centers across the world and fleets of portable rigs, supported by highly-trained engineers are available for direct plant visits. Convenient and cost-effective, this mobile approach eliminates the need to ship instruments offsite.
Regardless of procedure, plants must understand their calibrators’ accreditation. Calibration should follow a chain of traceability, ensuring a connection to a national standard at the end of the chain, to keep measurements from becoming compromised.
Each organization’s competitive edge depends on accurate measurement and efficient production. By optimizing calibration procedures and using inline verification wherever possible, plant personnel can ensure profitable, compliant, and safe operation.