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CALIBRATION & MAINTENANCE MAKING MEASUREMENTS MORE MEANINGFUL
When we need to guarantee that process performance has been optimised it pays to ensure we are getting the best levels of performance from measurement and analytics equipment
Jon Davison, Product Specialist for pressure and temperature for ABB UK Measurement & Analytics, explains the growing importance of equipment calibration in promoting good practice and profitability
A
t a time when companies across all industries are under financial pressure, everyone is looking to squeeze the maximum value that they can from their assets. We all know that you can’t manage what you can’t measure, so maintaining an accurate monitoring and control regime is essential. That’s just one reason why it’s the right time to think about how well your calibration regime is supporting your business. Properly scheduled and effective calibration ensures that the readings emerging from instrumentation are accurate. Without it, measurements are essentially meaningless. This may be self-evident in some types of instrument, such as pH meters that rely on the sort of wet chemistry that can easily be disturbed. But even seemingly robust, solid state sensor elements such as thermocouples rely on electronics to relay their readings to plant control systems and electronic components are subject to aging from any number of factors, such as mechanical stresses or temperature fluctuations. Ensuring instrumentation is calibrated has an impact to the bottom line. However, the impact varies depending on the business. While flow meters carrying out fiscal measurements on petroleum products may
6 APRIL 2024 | PROCESS & CONTROL
need to be accurate to ±0.025%, a meter controlling the level in a water tank used for washing down machinery may only need to achieve ±10%.
It’s about optimising the process to generate the most income from the available assets, whatever your business. The ultimate goal might be increased production yields, reduced product give-away and over- charges, more consistent product quality and/or reduced product liability. Alongside process optimisation there is growing pressure for more measurement accuracy emerging from the legislative arena too. Environmental Permitting Regulations (EPR) regulate companies in the process and water industries and require them to maintain effective monitoring of their emissions to air and water.
Increasingly, EPR compliance requires plant operators to use monitoring equipment that has been officially approved under the MCERTS scheme and ensure regular calibration.
When should you calibrate? The right time to calibrate a specific piece of equipment will depend on the type of instrument and the nature of the job it’s doing. As a guide, instruments should be calibrated
when they are first installed, as per manufacturer guidelines, when a physical shock or vibration could cause damage, following severe weather or sudden changes in weather, or when the output seems doubtful The calibration frequency will also depend on how critical it is to the process. If high performance and accuracy is crucial to production, then the instrument should be checked regularly.
In safety critical applications, companies may need to have their pressure transmitters checked every 12 months in a SIL1 application or every three months in a SIL3 application, this frequency is determined by the target reliability required. It’s all about finding the calibration frequency that works for your business. When calculating calibration frequency, this five- stage process designed for pressure transmitters is a useful guide:
1. Determine the performance required for the application
Some applications have a direct bearing on safety or plant efficiency and therefore accurate readings in the order of 0.5 % of span or less. This will normally increase the required calibration frequency. If all that is needed is to indicate a performance figure of
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