| by Villy Lindfelt
Modern industrial plants, production processes, and quality systems place tight requirements on the accuracy of process instruments and process control, all of which require accurate measurement. However, even the best measuring instruments aren’t absolutely stable; they drift and lose their ability to give accurate measurements. This makes calibration necessary.
Calibration is an essential element of any instrumentation-maintenance program and it requires managing information, assets, and reports. The need to maintain calibration procedures, follow the procedures, accurately record calibration results, and then act on that information can make calibration operations seem longer and more time-consuming than the processes that they’re designed to monitor. The problem grows exponentially with the number of gauges and sensors that must be maintained.
A large production plant can have thousands of instruments that require calibration. If they need to be calibrated once a year, this means performing thousands of calibrations and producing as many calibration reports. In addition, all of those calibrations must be planned around normal workflow, and information about all instruments must be documented.
The traditional method of calibration management--using pen and paper--is still the most common. Once the report is written, it’s put into an archive. This method is time-consuming, fraught with errors, and makes later analysis of the information nearly impossible. Another common method is self-made computer-based systems, such as an Excel file. Information is stored in an electronic format, but the process of documenting calibration information is still slow and prone to human error.
Computer-aided calibration management is becoming more common due to increasingly tough requirements set by regulatory authorities and quality systems, the need to improve calibration-related work productivity and efficiency, and the need to increase system automation. All these factors support the use of calibration software instead of pen-and-paper-based systems.
The biggest benefits are gained when using calibration software that communicates with documenting calibrators that can be integrated into a maintenance- management system. In such a case, the calibration software becomes the heart of the company’s calibration operations. The following time-saving functions are among the automated chores that such software can perform:
• Upload calibration procedures from calibration software to calibrators. Before performing any calibrations, you can upload from the calibration software to your field calibrator or workstation all the calibration procedures you have to do. No need for pen and paper.
• Download calibration results back to calibration software. When the calibrations are done, you can download all the calibration information and results from the calibrator back to the software. It’s fast and efficient.
• Manually enter calibration data into calibration software. If you like, you can also manually enter calibration information into calibration software. This way you can store and manage all possible calibration standards with the software, no matter what you calibrate.
• Mobile calibration management with a Pocket PC. Using calibration software with a Pocket PC interface for downloading and uploading calibration information makes an entirely paperless calibration system possible.
• Create, manage, and store calibration information safely and efficiently. All calibration data, procedures, and results are stored and managed in the calibration software’s database. Ideally, it’s in an auditable and traceable format, and it adheres to regulatory requirements, such as ISO/IEC 17025, current good manufacturing practice, and FDA 21 CFR Part 11.
• Integration to a maintenance-management system (MMS). Plant hierarchy and work orders are stored in an MMS and from there transferred to calibration software, which stores all calibration procedures, standards, and results. When calibration work has been performed, calibration software sends an acknowledgement of the calibration back to the MMS.
• Create calibration certificates, reports, and labels in electronic format, on paper, or both.
As the above list shows, modern calibration software can automate and simplify calibration work at all levels, particularly when used with a documenting calibrator. In addition to those items listed, it can automatically generate a list of instruments waiting to be calibrated in the near future. If the software can interface with other systems, calibration scheduling can be done within the maintenance-
management system, and work orders automatically loaded to the calibration software.
Measurement ranges and error limits of the instrument are defined in the software and downloaded to the calibrator. Thus, the calibrator is able to detect if the calibration passed or failed immediately after recording the last calibration point; there’s no need to make tricky calculations manually. This results in major time savings and increased productivity. While the calibration results are being uploaded to the database, the software can detect the calibrator that was used. The traceability chain is documented without further action from the user.
Calibration records, including the full calibration history of an instrument, are kept in the database; therefore, accessing historical results can be done in a few seconds. When an instrument has been calibrated several times, modern calibration software can show the historical trend to help users decide if the calibration interval should be changed.
The experience of Croda Chemicals Europe of Goole, East Yorkshire, in the United Kingdom, is typical. The company uses pressurized vessels to purify lanolin for health care and beauty products. Each vessel must be certified at least once every two years to demonstrate that it’s safe and structurally sound. That certification includes a functionality check on all the pressure instrumentation as well as the sensors that monitor incoming chemical additives and outgoing effluent.
David Wright, the senior instrument technician, remembers what it was like to perform all of those calibration operations with pen and paper during the company’s regular maintenance shutdowns. “It took us a week to perform the calibrations and a month to put together the paperwork,” he recalls. Today, Croda uses calibration software to coordinate the data-collection operations and archive the results. “It’s faster, easier, and more accurate than our old paper-based procedures,” says Wright. “It’s saving us around 80 man-hours per maintenance period and should pay for itself in less than three years.”
Their system can be connected directly to several kinds of calibrators and is capable of tracking predefined, customized process instruments and calibration standards such as pressure, temperature, electrical, indicator, recorders, and mass. A multidimensional plant hierarchy with uninstalled, installed, and spare equipment can have multiple functions, procedures, and work orders, including equipment classification.
Once a calibration task has been performed, the software is able to record the calibration history together with time stamps, electronic signatures, record status, and a complete audit trail. These functions are especially necessary in regulated industries, such as pharmaceuticals, where routine calibration is required to show that quality-critical instruments continue to perform within defined tolerances. The records that are produced must be stored and retrievable upon demand to demonstrate to an auditor that the plant is being maintained at an acceptable level. The software complies with the new legislation concerning electronic records and signatures, as defined in the regulations set forth in FDA 21 CFR Part 11. The software can also be integrated into a maintenance-
management system, such as SAP or Maximo.
Calibration software can also help with planning calibration operations. Calibration schedules take into account the accuracy required for a particular sensor and the length of time during which it’s previously been able to maintain that degree of accuracy. Sensors that are found to be highly stable need not be recalibrated as often as those that tend to drift. The trick is determining which sensors should be recalibrated after a few hours, weeks, or years of operation, and which can be left as-is for longer periods without sacrificing quality or safety. Doing so allows maintenance personnel to concentrate their efforts only where needed, thereby eliminating unnecessary calibration work.
The calibration schedule at Croda is determined by three criteria. The company must first comply with all governmental and insurance regulations that mandate protection for the plant, its personnel, and its environment. These are Croda’s top priorities and in some ways the most expensive, not so much for the direct costs of complying with the mandated calibration operations, but for the potential cost of failing to comply. In the United Kingdom, as well as the European Union and the United States, government agencies can shut down a plant for violating health and safety regulations, including violations relating to calibration.
Second, Croda enforces its own in-house safety and quality standards that require certain sensors to be checked every week, every time an area of the plant shuts down for maintenance, or every year. The most frequent calibrations are reserved for critical sensors, such as the pH meters that measure the acidity of the effluent discharged into the river.
Wright describes Croda’s third criterion for calibration planning as “experience of practice.” Management analyzes the history of previous calibration operations and determines the optimal interval between calibrations for sensors that don’t require regular checks. This analysis can be performed automatically with calibration software, thereby improving the efficiency of calibration scheduling and relieving maintenance personnel of the need to remember when a particular sensor is due for calibration work.
By maintaining calibration schedules for all the sensors in the plant in one electronic database, calibration software can reduce the administrative headaches of maintaining individual schedules for individual machines, processes, and operational zones. Automatic archiving functions also eliminate the transcription errors common to handwritten calibration reports and work schedules, saving not only the time required to fill out a paper report, but also the time required to do it again if mistakes are discovered.
Accumulated wear and random variations in a sensor’s environment will inevitably reduce its accuracy over time, so periodic testing is required to guarantee that the measurements being reported actually match the conditions being monitored. Otherwise, any computerized monitoring or control system to which the sensor is interfaced will be unable to detect off-spec conditions, and the quality of the product being manufactured will suffer. Unfortunately, calibration operations can be long and tedious, even with the aid of an electronic calibrator that automates the tests. The sheer volume of data that must be collected and analyzed can be overwhelming when hundreds of sensors must be checked and multiple data points recorded for each. By planning the process beforehand and adding the right tools, calibration efficiency can be improved and costs lowered substantially.
Villy Lindfelt is the marketing director of Beamex ( www.beamex.com ), a company that has been providing calibration solutions that improve efficiency and productivity since 1975. Beamex’s comprehensive product range includes portable calibrators, workstations, calibration software, accessories, industry-specific solutions, and professional services.
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