Just as manufacturers have moved from clipboards and hand-written data collection to automated electronic systems for batch records, many are doing similar things for field instrumentation calibration. In addition to being less labor-intensive, these newer approaches make the documentation less prone to error and more suitable for presentation to regulatory groups.
This dovetails with changes on the verification side. FDA/ICH Guidances for Industry describe verification as a continuous process with three key elements:
- Detect unplanned departures from normal operation
- Collect and analyze product and process data related to quality
- Maintain facility including qualification of equipment.
The third element includes instrumentation calibration. It is nonsensical to imagine operating a critical manufacturing process or plant without verifying the information coming from instruments as true and accurate. If a process has been validated based on a specific reaction happening at 85ºC (±1 ºC), verification ensures the temperature instrument monitoring the reaction is accurate and capable of delivering a reading with an appropriate degree of precision every time.
Understanding Calibration Regulatory Requirements
The Code of Federal Regulations Title 21, Part 211.68 says automatic, mechanical or electronic equipment can be used in drug manufacturing, and if it is used, “It shall be routinely calibrated, inspected or checked according to a written program designed to assure proper performance. Written records of those calibration checks and inspections shall be maintained.”
This regulation places the burden for creating a compliant calibration program on the facility. It does not specify how or how often any specific instrument must be calibrated or checked. At the same time, when the facility is being inspected by a government agency for regulatory compliance, those details will certainly be examined. A facility will have to defend its calibration practices within its larger validation and verification programs.
So ask yourself if your calibration program is appropriate for the instruments you’re using today, or if it still reflects the needs of less sophisticated process instruments of years past.
Streamline Calibration Record Keeping
Electronic records for product movement and manufacturing have largely replaced expensive and troublesome manual techniques. Unfortunately, in a surprising number of facilities, manual recordkeeping for process instrument calibration and maintenance persists. Since calibration tasks tend to be manual by nature, recordkeeping by hand often follows, but better methods are available.
Just as electronic batch records improved manufacturing processes, they can also do the same for calibration. Consider the typical steps for a temperature sensor:
- Find the appropriate instrument, identify it positively, and remove it from its mount
- Find the relevant test and calibration protocol for the specific instrument
- Heat up the dry-block calibrator to the first test point and take the first reading
- Reset the dry-block temperature, wait for it to change to the new value and repeat the reading
- Do this as many times as specified, typically five test points for a critical instrument
- Write the relevant information on a test sheet, or type it into the computer terminal
- Write out the calibration sticker and return the instrument to service or the stockroom.
A technician working under pressure and in a hurry might inadvertently write down incorrect information. Other typical mistakes include testing the wrong instrument, testing to the wrong set of calibration points, testing against an incorrect standard and so on. In any situation where a human being has to read and write numbers, mistakes will be made. While automating calibration to the extent of removing the human element entirely isn’t possible for all instruments, there are ways to automate calibration and recordkeeping.
Smart Instruments Simplify Procedures
Smart field instruments have the ability to communicate well beyond simply sending an analog process variable. Protocols such as HART and WirelessHART provide the means for a smart transmitter to store a great deal of configuration and calibration information, including:
- Its own tag number
- Measuring units and range
- Calibration history
- Calibration test points
- Self-diagnostic functions
- Alarm points, and more.
These capabilities have greatly improved the calibration picture. A smart transmitter can be linked to control and monitoring systems via a digital data network, which can communicate its internal diagnostic information along with the basic process variable. Since verification is a process rather than an event, it is possible to monitor the condition of all process instruments on a unit continuously while the process is running. Internal diagnostic routines can warn of a problem developing with any instrument.