Process Calibration (Part One)Calibration Is An Important Aspect Of Maintenance
Calibration of process instrumentation is a necessary function for two main reasons. One, to comply with regulation; and two, to maintain and control process performance and product quality.
Regulation is vital to ensure plant and process safety and calibration is now mandatory throughout the process industry. Regulation is also especially important where traceability is vital to ensure the quality of sensitive products such as in the pharmaceutical sector.
Calibration for process and product quality control is something that improves the bottom line. Product quality must be maintained and monitored to eliminate any wastage issues or customer litigation. Process performance must be monitored to ensure efficiency of operation as well as plant safety.
But what is calibration?
Basically, calibration involves the comparison of two instruments or measuring devices, one of which is of known accuracy, to establish the accuracy, or otherwise, of the device to be calibrated. Calibration is necessary because all measuring devices drift over time and calibration is carried out to ensure we are measuring to the accuracy required, accuracy set on installation or accuracy set later to some agreed value.
“ When to calibrate is often asked. Some calibrate strictly to manufacturers’ recommendations. Some calibrate on a regular frequency basis, such as annual shut-down. Historically, such calibration sometimes involved taking the measuring device out of service and sending it to a calibration lab. Here calibration tests are carried out by instruments which are verified to national standards and labs are audited by national standards authorities. ”
Today’s laboratory calibration equipment offers easy communication with software and can provide 100% automated calibration of pressure transducers and transmitters. However, this is not a perfect solution because, naturally, instruments can drift between these calibration intervals. An obvious answer to this is to calibrate more frequently, but this entails increased time and cost, both in lost production and in calibration resource.
Fortunately, today’s calibration management software can analyse collected calibration data and determine the optimum calibration frequency for each instrument or measuring device, based on a set of programmable operating scenarios and safety margins.
Automating the Calibration Process
Naturally, calibration is an important aspect of maintenance and if calibration data is analysed correctly, it can help maintain and improve compliance, efficiency, quality and safety. However, managing the calibration of 1000s of plant instruments and then analysing all the data to a level required for trend evaluation is not a simple task. Even today, a surprising number of organisations still use pen and paper to record calibration results. This can mean that an instrument engineer can spend as much as 50% of his time working on documentation and paperwork, preparing calibration instructions, making notes of calibration results in the field and documenting and archiving data. Apart from the valuable time involved, paper-based recording also brings with it the chances of transcription mistakes.
Today’s advanced portable calibrators can store a vast amount of data and can even be used to create and review calibration certificates and custom reports, which can be electronically signed off. This data can subsequently be transferred to a PC when convenient for printing and archiving. Calibration management software is available to automate the calibration process by stepping through the test points, calculating errors and reporting Pass/Fail conditions.