When measuring using an instrument, end users have to be sure that the equipment provides accurate measurements. With time and constant use, instruments may deviate from the accuracy they once provided. If this happens, it does not mean the instrument no longer works or that the end user should discard it. All one needs to do is calibrate it to see accuracy back on the charts. While people may define instrument calibration differently, the principle remains the same.

The process of instrument calibration compares measurements of known and unknown accuracy or precision. The instrument with unknown performance is called the “unit under test” or the “test instrument,” while the other is called the “calibration standard” or simply “standard.” Through instrument calibration, accuracy to the required standards is achieved.

Importance of instrument calibration

Calibration defines the quality of the measurement parameters — such as range, accuracy and precision — as recorded by an instrument. No manufacturing process is complete without instrument calibration. It forms a crucial aspect of the quality assurance and testing phase, which is a critical part of many industries and sectors. This makes calibration important for virtually every industry, particularly those that are critically regulated by authorities such as the U.S. Food and Drug Administration (FDA).

The quality of measurement of almost every instrument will begin to wane with time and use. Such “drifts” or “shifts” need to be tracked and corrected before they affect the quality of the final product. For example, in pharmaceutical manufacturing, any change in the quality of the products can directly affect the health and lives of the users. This makes instrument calibration an absolute necessity.

All the instruments that utilize a certain kind of technology or are responsible for measuring shifting parameters — such as pressure, humidity or temperature — are prone to developing a drift in accuracy. Additionally, for some products, maintaining their quality is directly proportional to the quality of the measurements. Ensuring that the concerned instrument operates within an acceptable range of error is of paramount importance. For both of these cases, calibration is vital.

Regardless of what causes a shift in accuracy or how crucial accurate measurements are for maintaining the required quality of the products, regular and periodic instrument calibration is advised. Along with validation and qualification, calibration ensures that pharmaceutical manufacturing standards are maintained to the highest level.

The process

Instrument calibration is one of the chief methods of checking and maintaining the quality and accuracy of measurements. All these measurements are compared with the standard and accepted accuracy. If any discrepancies arise, the instrument is configured to provide results that lie within the acceptable precision, accuracy and repeatability range.

This is a good manufacturing practice that focuses on eliminating or minimizing factors that are responsible for errors or inaccuracy. Not all instruments are calibrated in the same way. The instrument calibration method varies depending on the instrument, although the basic steps below remain the same:

The calibrators (test samples or standards with known values) are measured using the test instrument.

The results are compared with the actual values, which provide a relationship between the measurement technique and the known values.

Calibration is carried out to minimize the difference, if any. After the calibration services are completed, the instrument can measure unknown samples with higher accuracy and precision.

Instrument calibration ensures that the instruments perform with high accuracy without compromising the final quality of the product. They perform best when they are calibrated following the manufacturers’ recommendations.

Accuracy factors

Instruments may show a drift in accuracy for many reasons. While calibration ensures that the accuracy is preserved again, carrying out the process in an environment devoid of factors that may affect the instrument calibration is critical. Several factors may affect calibration, which will further affect the end quality, rendering the objective of calibration useless. Three of these factors are discussed in this section.

Wrong values 

Calibration of any instrument needs to be completed exactly as instructed. Trying to choose the wrong values or disregarding documentation changes the way the instrument behaves. Using the wrong values produces notable errors within the operating range of the instrument. Even though newer instruments have a built-in software diagnostic system that can alert the operators if the order in which calibrators are tested is wrong, they cannot distinguish between calibrators that use the wrong values. Therefore, extra attention should be used to ensure that the correct values are used.

Wrong calibrator

Calibrators are the essential components required for instrument calibration, which makes it important that the calibrators used are manufactured by trustworthy and reputable calibration labs or manufacturers. The quality of calibrators has the potential to directly affect the results of instrument calibration. Only calibrators built to precise tolerances and specifications should be used for getting repeatable results and performance. Another tolerance associated with the formulation and design of a calibrator is because of the normal inaccuracies in the instrument and quality control processes. Be sure to use the ones with the right formulation tolerance required for the instrument being calibrated.

Ambient conditions

Ambient environmental factors — such as pressure, temperature and humidity — have significant effects on the results of calibration. Instruments should be calibrated in an environment that resembles the one in which they will operate. If variations in the ambient environmental conditions occur, they will affect the calibration process. For example, instruments calibrated in fluctuating temperatures will be prone to temperature-induced errors when operated in a different environment. Variations that may affect calibration should be minimized to achieve accurate results.

Diagnosis

During instrument diagnosis, the end user determines which instruments need calibration and which do not. Not every instrument requires calibration attention. Devices that are critical to product safety and quality should be priority. Through instrument diagnosis, personnel will determine which instruments could be moved from a periodic schedule to on-demand calibration. If the instruments are not directly involved in the production of pharmaceutical products, they can be shifted to on-demand calibration instead of subjecting them to a periodic schedule. Others must be calibrated frequently to comply with pharmaceutical Current Good Manufacturing Practices (CGMPs).

With the help of predictive maintenance software, end users can obtain crucial data from field instrumentation. They can analyze and monitor a selected group of instruments that are less critical, and as soon as they indicate a change in measurement accuracy, a regulatory inspection and a calibration check should be completed. By having a condition monitoring program for conducting on-demand calibration, hundreds of potentially unnecessary calibrations per year can be eliminated. These on-demand calibrations need to be performed in a highly efficient way.

Paperless procedure

Calibration has been a manual task for decades. With calibration software, calibration has become automated and paperless. The software helps streamline calibration, optimizing periodic calibration schedules and electronically synchronizing all the data related to calibration. This data can be accessed by the technicians from any device at any location. They can even download the required data when needed onto their mobile devices.

By making calibration a paperless procedure, companies save time and money. Administrative staff no longer spends dozens of hours manually entering the data onto paper. The whole process is faster and decreases paper use. Apart from data documentation and recording, even scheduling and analysis can be carried out without paper.

Analysis

In the past, calibrations were performed at specific time intervals, which were further extended whenever possible so the number of procedures performed in a year could be reduced. At the same time, even though the calibrations were extended, they remained in compliance with corporate regulations and policies. Now, the same is being achieved through computer-driven analysis of the historical data that identifies instruments that do not need to be calibrated as often as others. This is an ongoing process and accurately determines which
instruments need calibration and how often.

The schedule of calibration holds importance, too. An end user must ensure that all instruments related to safety and quality are calibrated on schedule. Calibration analysis determines when each instrument should be calibrated, and its performance is closely monitored.

Software-based management

The efficiency and quality of calibration can be improved by integrating the instruments with an automated calibration system, which provides several advantages. With software-based calibration management, end users can:

  • Automate calibration work from beginning
    to end.
  • Efficiently create, store and manage calibration data.
  • Share a database with other plants.
  • Achieve seamless communication with documenting calibrators.
  • Experience paperless calibration management.
  • Get integration into a maintenance management system.
  • Achieve regulatory compliance — for example, International Organization for Standardization (ISO) 17025, ISO 9001 and FDA.

Accuracy & efficiency 

End users can achieve accurate and efficient
calibration by:

  • Replacing individual devices and reducing recalibration devices with multifunctional calibrators
  • Using automated calibrators with documenting capabilities and automatic error calculations
  • Having seamless communication with a
    calibration software
  • Implementing reliable and robust calibrators
  • Supporting different instruments and protocols such as Profibus, HART and Foundation Fieldbus

Advantages

Implementing an integrated calibrated solution provides seamless communication between calibrators and the calibration software. Further, three things
are achieved:

Improved efficiency — Integrated calibration solutions simplify and automate all the processes involved in calibration, from beginning to end. They reduce production downtime and are fast and easy to use.

Cost savings — The solution helps replace paper because the records can be stored electronically and the database can be shared with plants worldwide. With multifunctional calibrators, recalibration costs are also reduced.

Improved quality — Human error related to the documentation of calibration data is minimized significantly. The integrated solution helps create, store and manage all the calibration data safely and efficiently. Moreover, it can help achieve regulatory compliance — such as CGMP; 21 Code of Federal Regulations, Part 11; and ISO 9001).

Apart from this, calibration software allows end users to perform smart analyses and calibration data management.

Conclusion

The importance of instrument calibration in different industries cannot be emphasized enough. It is the most basic, yet crucial maintenance requirement and is an established procedure that should be conducted by any industry that uses instruments and machinery to manufacture products. Calibration should be conducted periodically or on-demand as required by the instrument and its importance to the process, but it must not be skipped for any reason. With proper instrument calibration, end users get improved efficiency and products that will always achieve the desired quality.

Edward Simpson is a seasoned calibration and technical engineer for RS Calibration Inc. Simpson has a knack for finding faults in machines and does not rest until they are rectified to perfection. He lives in Pleasanton, California, and can be contacted anytime for matters related to machines. For more information, visit rscal.com.