Temperature, pressure and level measurement equipment plays a huge role in pharmaceutical Current Good Manufacturing Practices (cGMP) and quality assurance, so it is essential for these devices to be checked for accuracy on a regular basis.
This can be done through instrument calibration, the process of comparing measurements from a device against a standard. The standard is a device with known accuracy, traceable to national or international standards. Deviation from the standard (uncertainty or “drift”) is recorded and the instrument under test may then be adjusted to correct it.
Calibration is particularly important for process-critical devices, where measurements affect final product quality or safety.
How is instrument calibration performed?
Calibration may be performed in-house or by sending equipment to a calibration laboratory. Depending on the frequency, number of devices tested and the type of equipment used, it may be easier to use calibration services to ensure measurement devices are accurate and their results are traceable.
Accredited labs provide on-site calibration, which can save the additional cost of investing in testing equipment and training personnel for calibration and testing activities. Since most pharmaceutical companies use a wide range of devices for temperature, pressure and level measurement, this can add up to a huge expense.
Time can also be saved. Performing calibration in-house can mean a lot of downtime, but labs providing calibration services have the experience, equipment and training to minimize the amount of time devices are out of service.
Common types of temperature sensors
Temperature measurement devices typically used in pharmaceutical manufacturing processes include:
- Spring-type or bimetal thermometers
- Resistance-temperature detectors (RTDs)
- Infrared radiation (IR) detectors
- Thermal imaging cameras
Why is calibration important for temperature sensors?
Temperature sensors are critical to pharmaceutical quality assurance since even slight variations in temperature can affect product quality and safety. Thermistors, IR thermometers, RTDs, thermal imaging cameras, thermocouple probes and other temperature-sensing devices are also sensitive and prone to damage during use.
These devices need to be checked for reliability and accuracy on a regular basis, and the results of these tests need to be properly documented to ensure traceability. Frequent calibration helps with these activities, as well as the timely detection of any measurement drift or deviation caused by corrosion, rough handling or accidental damage.
How is calibration conducted for temperature-sensing devices?
Temperature sensors can be calibrated using a variety of methods and testing standards, including:
- Fixed-point cells/intrinsic standards – These are typically used only by calibration laboratories since the cost is too high for in-house calibration. They offer the highest accuracy for temperature sensor calibration.
- Liquid bath calibrators – These high-maintenance calibrators are generally installed in stationary locations such as calibration labs, and they are used for extremely small sensors or devices that have odd shapes.
- Dry-block probe calibrators – These are more portable, require less maintenance and reach desired temperatures more quickly than liquid bath calibrators, but they are not as accurate or stable.
- Electronic calibrators – These are the most affordable and portable calibrators for in-house testing, but they do not have a temperature source for testing the integrity of the sensor.
- Infrared calibrators – These are typically used for calibrating pyrometers, thermal cameras and other noncontact temperature measurement devices.
Why is pressure gauge calibration important?
A variety of pressure gauges are used in commercial settings, especially in the pharmaceutical sector. Manufacturers and laboratories alike rely on them heavily for a wide range of tasks, such as controlling process pressure, cleaning processes, filters and pumps, as well as monitoring filling levels and detecting leaks, etc.
Instruments that measure pressure are also critical to safety and quality assurance, so it is crucial to ensure they are reliable, precise and accurate. Regular instrument calibration helps pharmaceutical companies maintain the highest level of quality and safety in their manufacturing processes.
Common types of pressure gauges
While many pressure gauge types are available, some of the most common ones used in pharmaceutical manufacturing are:
- Commercial pressure gauges
- Industrial pressure gauges
- Process pressure gauges
- High-precision test gauges
- Low-pressure gauges
- Seal gauges
- Absolute pressure gauges
- Duplex pressure gauges
- Differential gauges
Why calibrate level measurement devices?
Level measurement is the process of determining the position or level of a surface within vessels such as tanks and reactors for accurate and reliable inventory control.
Along with temperature and pressure measurement, level measurement plays an important role in tank-gauging systems. These systems are helpful in the calculation of net volumes and inventory, plus they offer operational and safety benefits. Depending on the application, continuous level transmitters and point level systems may also be used for level measurement.
As with other process-critical measurements, instrument calibration can help ensure that level measurement results are accurate, reliable, repeatable and traceable to industry standards.
How often should measurement devices be calibrated?
The calibration frequency for any measurement instrument depends on a wide range of factors, including quality standards, damage risk, regularity of use and rate of drift. Consult an accredited lab for help with creating a calibration schedule based on equipment types used as well as unique process requirements.
Keep a few basic guidelines in mind:
- Follow the manufacturer’s recommendation for calibration intervals, which may be different for each measurement device used.
- For safety-critical measuring devices used in food and pharmaceutical manufacturing, daily or weekly calibration may be needed.
- Schedule calibration every six months or once a year for devices that are noncritical to quality and safety.
- Maintain a short interval between calibrations for process-critical devices, ideally on a monthly or quarterly basis.
- If a certain project requires calibrated and certified measurement devices, send them for calibration before the project begins.
- Perform calibration before the start of a critical project that requires highly accurate measurements, and again after it is complete.
- If any devices show signs of damage or wear and tear, check their safety integrity and make sure they are calibrated frequently.
Why use an accredited lab for calibration services?
AS 17025 or ISO 17025 is the quality management framework for calibration laboratories, which only receive accreditation if they satisfy all the requirements for quality and NIST traceability. It works the same way as ISO 9000 for manufacturing companies, offering the assurance that calibration services will be performed correctly.
Labs without accreditation may be able to provide good service and traceability, but companies need to verify these on their own. Checking that these labs use the appropriate methods and document procedures correctly typically involves a heavy investment in terms of time, effort and money, which can be saved by using accredited service providers.
An accredited lab can provide the appropriate calibration certifications for each piece of equipment so problems do not occur during regulatory inspections. Valid documentation is a critical part of Food and Drug Administration regulations and pharmaceutical cGMP, and failure to provide it can lead to penalties, fines and even product recalls.
When using any measurement instrument, accurate results are necessary. Proper calibration is the only way to define accuracy as well as ensure that the quality of measurements is recorded as per defined procedures.
Edward Simpson is a seasoned calibration and technical engineer who works for RS Calibration Inc. He has a knack for finding faults in machines and does not rest until they are rectified to perfection. Simpson lives in Pleasanton, California, and can be contacted anytime for matters related to machines. Visit rscal.com to learn more about the type of calibration work he does.