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Calibration and maintenance as a singular concept

19 September 2011

Mike Shelton, of GE Energy, Measurement & Control Solutions, discusses the advances made in combining calibration and maintenance into a single software package and the advantages such a unified approach can offer.

Calibration and maintenance of site instrumentation is vital for a variety of reasons -l to ensure that production output is achieved within set quality parameters and to meet regulatory requirements, for example. It is also a vital requirement if an efficient system of traceability is to be achieved.

Calibration and maintenance is a singular concept although the two activities are often viewed separately. Calibration can be carried in isolation, as can maintenance, but for maximum effect, they should be carried together to ensure that the results of calibration are incorporated into maintenance procedures.

Calibration involves the comparison of two devices, one of which is of a known accuracy. For the accuracy to have any real meaning, the standard itself should have traceability to a nationally or internationally recognised reference instrument, which has been shown to offer the smallest deviation from the absolute true value. Historically, instrument calibration has carried out once a year during plant shut-down. The drawback to this approach is that all instruments drift out of specification to some extent and the onset of this drift could be anytime within the 12 month operating period. Of course, it would be possible to calibrate more regularly but this would have cost and resource implications.

Today, calibration management software is able to analyse collected calibration data and determine the optimum calibration period for each instrument. Apart from providing better audit-ready status to comply with regulations and legal requirements and to ensure plant safety, calibrating critical instruments more often and keeping them within tight operating limits can also have a beneficial effect on quality and efficiency. Today’s software can also indicate where calibration periods could be extended, without the instrument going out of specification.

Collecting the data
Some instrument engineers believe that calibration cannot be properly performed out of the calibration laboratory where it is not possible to control the effects of temperature, atmospheric pressure, humidity. Today, however, laboratory pressure calibration equipment, such as the PACE platform from GE, has been designed to communicate with software, specifically developed to provide support for both laboratory and field calibrations, providing control in a fully integrated pressure loop, giving 100% automated calibration of pressure transducers and transmitters. The software has documenting facilities to prepare reports and provide calibration certificates from its database, utilising readout data from connected calibration equipment and test devices. In addition, calibration and maintenance history, along with configuration, is stored within the instrument. This is updated each time a calibration is carried out.

Portable calibration instruments for on-site application have advanced to the point that they can now be used in a range of climates and within well-defined limits. The latest compact calibrators, such as the DPI 620 from GE, can simultaneously measure and source electrical, temperature and frequency signals and provide loop power. Simple screw-in modules and snap-on generators allow extensive pressure applications. The versatility of these instruments has also been increased by incorporating configuring and commissioning capability, which turns the calibrator into a communicator and contains a library of registered HART device descriptions to support more than 1000 sensors.

Calibration software
Calibration management software began as PC-based software, where the instrument database and history was held on a PC and the technician downloaded information relevant to his workload, carried out the required calibrations and then up-loaded the results and data so that reports could be produced and records maintained.

Recent developments have created portable calibrators with the power of a PC-based calibration system, allowing management of a plant’s instrumentation inventory from a portable device in the field. This allows the field engineer, without reference to a remote PC, access to information such as device details, calibration history, trend analysis and calibration procedures, as well as all the necessary supporting documentation. It also allows new device records and procedures to be created in the field while giving access to historical data. Calibration and documentation is automated. Regulatory compliance is improved by scheduling work procedures and documenting calibrations and actions. Data can be transferred to a PC at a convenient time.

Combining calibration and maintenance
If calibration data is analysed correctly it can help improve compliance, efficiency, quality and safety. However, managing the calibration of 1000s of plant instruments and then analysing the data to a level required for trend evaluation is not a simple task. It involves scheduling, resource management and cost analysis, as well as the challenge of storing all the data and documentation to the satisfaction of an auditor.

Currently managers tend to use manual methods for gathering data, store and process the data by means of an in-house spreadsheet application and then employ various means to plan and schedule maintenance activity.

There are basically two types of calibration software - software from calibrator manufacturers, which are tied to the manufacturer’s hardware; and software from software companies, which does not come with hardware solutions. Many organisations want to move forward with fully integrated software-based solutions but find it difficult to justify or obtain the IT infrastructure or support required. Some organisations have adopted high-end, computerised maintenance management systems (CMMS), which will schedule maintenance activities but offer no tools for organising resources, defining procedures, gathering and analysing the data.

A recent software development combines calibration and maintenance management and offers a way to streamline maintenance workflow by improving data integrity, scheduling work activity, automating calibration and maintenance and correcting deviations. It offers a paperless system with e-signatures for regulatory compliance. At the same time 4Sight software, which can interface with CMMS, provides audit ready data in compliance with the most stringent quality systems including FDA and GAMP with full, 360°management reporting tools.

A web-based solution
Most software today has to be installed on a PC, even when it is a server-based installation. From a maintenance point of view, this means that the server database and the PC applications have to be installed and periodically up-dated. The latest web-based technology allows software to be installed on the company’s server and accessed through any internet enabled device from anywhere in the world. Alternatively, the software can be hosted by a third party as a service on an external server, so that there is no need for software installation and IT support at the company itself. In either case, the software, database, upgrades, etc are all handled externally and the company has no IT overheads.

Resource management and efficiency improvement tools are other features of the new software. An Interval Analysis module allows users to report on device performance by scientifically analysing historical data and drift. This tool helps calibration managers tasked with increasing calibration intervals to come to a researched and informed decision, providing reporting and analysis quickly and accurately. Similarly, Key Performance Indicators update in real time to allow performance of the installed base and resources to be analysed and compared across the whole business or at different levels. Vision deviation management ensures that calibration failure notifications are sent in a timely and controlled way, so that users can record the cause of deviations, investigate the reason and work to a resolution. The audit trail will then demonstrate that a robust solution is in place to manage deviations and that strict procedures are enforced for corrective action/preventative action.

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