05 July 2001
Document all maintenance activities
by Todd Gates
Asset management system interfaces to self-documenting calibrators.
Industrial managers are desperately trying to reduce production costs, or at least hold the line on rising expenditures.
Improper or unnecessary practices waste an estimated one-third of maintenance expenditures. According to a report issued by the E. I. duPont de Nemours Co., "The largest single controllable expenditure in a plant today is maintenance, and in many plants the maintenance budget exceeds annual net profit."
Maintenance averages 14% of the cost of goods sold in many industries, making it a prime target for cost reduction efforts. Traditional belt tightening and budget slashing negatively affects quality, productivity, and employee morale. A better solution is utilizing emerging technologies designed to streamline maintenance practices and reduce waste.
Until fairly recently, device manufacturers provided "point solution" applications for configuration and maintenance of their own products. This approach has a number of disadvantages, not the least of which is the lack of a common user interface and the need for multiple platforms to run these software programs.
|Software lets users communicate with live instruments in the field and access all instruments' historical records by simply clicking on an instrument icon.|
Many similar tasks unnecessarily overlap in these proprietary applications, yet engineering cannot monitor all devices simultaneously, nor can it log all instrument events in a central location.
Asset management software (AMS) designed to integrate diverse technologies and device management functions into a single platform has changed that paradigm by providing online access to field instrumentation and saving all maintenance-related information about plant devices in a single database.
Devices are data servers
Information about each instrument is organized and processed to accommodate various maintenance functions, including online configuration; continuous monitoring of the field, which forms the basis for predictive maintenance; and automatic documentation of all maintenance activities.
Here are the three parts of asset management:
- Smart field devices that gather and disseminate information about their operational status and that of associated equipment
- Open communications allowing transmission of information from transmitters, valve positioners, and other devices, regardless of manufacturer, to a dedicated PC in the maintenance shop
- Software with built-in tools to help maintenance personnel do their jobs more efficiently and accurately
Intelligent, microprocessor-based field devices exist primarily for control purposes, but they also function as data servers, providing information about their operational status, the state of the process, and even the condition of the equipment to which they are attached.
Intelligent field devices, such as temperature and pressure transmitters, report up to 50 status conditions related to the health of their electronic software and sensor components. New devices support even more functions, such as early detection, isolation, and analysis of anomalies.
Such information is the foundation for asset management.
This new software can have a positive economic impact in the management of regular, periodic calibration of field instruments. One pharmaceutical company, which calibrates 8,000 devices per year, reported estimated annual savings of $264,000 in reduced calibration time. This savings is made possible in three ways:
- The test scheme for each instrument is in a database and downloads directly into a self-documenting calibrator.
- The database predefines and maintains routes. This guides technical personnel in grouping instruments so they can jointly calibrate instruments most efficiently.
- Essential documentation for regulatory compliance and maintenance scheduling comes from the test results, which are on the calibrator. The results store automatically, per instrument, into an archive.
In regulated industries such as pharmaceuticals and food processing, instrument calibration not only is mandatory but also must happen at or within specified time intervals. Further, each company must document its compliance with the regulations.
Annual calibration of all instruments is common, and in plant areas where instrument accuracy is critical to product quality, calibration every six months—or even more frequently—is not unusual.
Calibration is equally important in nonregulated industries, where many companies test their field instruments annually to maintain functionality and ensure process efficiency and quality. In one plant, a maintenance supervisor acknowledged that calibration normally happens every other year, and sometimes an instrument is totally inoperative by the time a technician tries to do calibration testing.
|Users can graphically display and print the results of calibration tests. The complete calibration history of each instrument is in memory. Users can overlay graphs to monitor instrument health and fine-tune calibration intervals.|
In the press of everyday activities and the need to complete assignments, technicians sometimes neglect the final step: documentation.
Define the test scheme
Most maintenance departments follow the same procedures for calibration they've used since handheld, self-documenting calibrators became available. The procedure goes something like this:
- A calibration route is established for each group of instruments—generally grouped by area of the plant but possibly by instrument type or the date on which particular instruments need calibration.
- A calibration scheme, including all test parameters, defines each instrument. The scheme includes the specific test points, such as different levels of pressure or different temperatures the test equipment should use and how the instrument should respond.
- Accuracy, in terms of maximum error or tolerance of error, is also part of the calibration scheme. Frequently, the technicians have to go into file cabinets and pull out the test requirements on each instrument in the group to be tested. If the instruments on a particular route are not of the same type, as is generally the case, the technician has to gather information on a diverse range of transmitters, valve positioners, flowmeters, and other devices.
- After defining the test scheme for each instrument, the technician must manually enter data into a handheld, self-documenting calibrator. This is normally a matter of punching the data in a predetermined sequence or code into the keypad of the calibrator. This is a time-consuming and error-prone process.
- The technician goes into the plant and attaches the calibrator to each instrument in a prearranged order. The calibrator applies the correct pressure, temperature, or other source and records the readings from the instrument. It compares that data with the source information to determine accuracy. Testing continues until all instruments on that route comply.
- If an instrument fails the calibration test, the technician must make adjustments and retest to be sure the calibration is correct. Failing calibration, the technician will swap out and calibrate a new instrument.
- When the technician finishes, he returns to the maintenance shop and writes a report on each tested instrument using the stored data in the calibrator. This is another tedious, time-consuming process.
- The technician files the reports for future reference or to prove to an inspector that calibrations took place that comply with regulations.
Technicians may test and document up to eight field devices in an 8-hour day.
The latest software automates key parts of the calibration process, thereby reducing human involvement and the chances for human error:
- It stores the calibration scheme on each installed field device in the instrument database.
- It maintains calibration routes.
- It downloads the calibration schemes for those devices on a route into the calibrator before a test cycle begins.
- It uploads the test results to the AMS.
In many respects, testing proceeds as before. But with AMS, when the cycle in the field is complete, the technician returns to the maintenance shop, attaches the calibrator to the PC again, and instantly uploads the test results to the AMS.
This data transfer is fast, error free, and easy. The calibration results are archived with all the other maintenance information for each instrument tested, automatically providing the documentation required to comply with the regulatory agencies.
Place for history
When anyone needs to know the calibration history of any device, he simply selects the icon for that instrument and goes to calibrate, and all of that device's calibration records immediately appear on the screen for reviewing or printing.
The software supports both smart and conventional analog instruments. Even though the software cannot communicate with conventional instruments, it maintains their calibration schemes and other pertinent information in the instrument database.
Thus, the calibration settings for every instrument in a plant can live in the calibrator. Calibration test results for conventional instruments can also be uploaded from the calibrator and stored in the database, along with results from smart field device tests.
Extended calibration capabilities eliminate the manual, error-prone data entry of calibration schemes into self-documenting calibrators prior to testing, as well as the need for handwritten or manually typed documentation of the results of calibration testing. Savings of $25 to $100 per device calibration are typical. IT
Figures and Graphics
Todd Gates has a chemical engineering degree and 15 years of experience in the process control industry. He is a member of ISA and works at Emerson Process Management as a marketing manager.