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Making the most of your measurement devices

10 July 2023

Without accurate readings of parameters such as flow rates, pressures and temperatures, production operations would grind to a rapid halt. David Lincoln explains how condition monitoring will help decrease unexpected downtime.

Devices such as flow meters and pressure transmitters keep plants up and running and processes running efficiently. But, is enough attention paid to the health of these instruments – who monitors the monitor and how is it done in a way that improves the efficiency and performance of the whole plant?

By implementing condition monitoring it is possible to schedule maintenance in a timely way and prepare for it in advance – for example by ordering spare parts. It is also possible to make use of the increasingly rich data that can be provided by measurement devices to formulate strategies or techniques to prevent problems from recurring.

Today’s process instrumentation is largely digitally based. As such they produce information, not only about the behaviour of the parameters they are designed to measure, but also about their own performance and accuracy. Many modern devices can check their own circuitry, help with their own calibration and evaluate their own performance.

Yet, these capabilities are not as widely used as they could be. Although most measurement devices are digital, many applications continue to use the tried and tested 4-20mA current loop, rather than digital communications networks. A myriad of technologies and techniques can be used to gather data and transmit it, with varying levels of information available dependent on the technology used.

For example, many 4-20mA measurement devices also offer HART communications – a bi-directional  protocol that provides data access between intelligent field instruments and host systems. The communications link carries the process values, like flow rates or temperature. Ultimately the best solution for data communication maximising the available data feedback from field instruments will be the use of Ethernet communications. However, Ethernet roll out may be complicated by a number of factors, the biggest of which is the complexity of implementation alongside legacy systems and interoperability.

Many advanced digitally enabled measurement devices will also offer sensor checks, including internal connections; an indication of sensor memory failure and an internal electronics check.

Remote condition monitoring
Remote condition monitoring may have existed before the pandemic, however, the ability to check-in on instrumentation remotely has come to be expected today. 

New software is allowing companies to manage instrument data plant wide, or even across a fleet of plants allowing for more accurate predictions of instrument health and maintenance requirements.  Data is collected remotely from field devices, analysed and reports are fed directly to a phone, tablet or laptop to allow the operator to monitor the condition and performance of instrumentation devices in real-time. The new generation of remote condition-monitoring and verification platforms for use with digital devices connect the physical and digital worlds through information technology (IT) and operational technology (OT) convergence. 

Field verification
One of the most important aspects of maintaining a device’s accuracy is field verification. Various factors, including environmental changes, shock conditions such as vibration or mishandling by operators, can cause the calibrated settings of instruments to drift, potentially impairing their accuracy. Although much condition information is available through the HART connections, this does not provide enough detailed diagnostic information to determine if the device has drifted away from the parameters set at the factory or during commissioning.

In such situations, the best option is to have the device re-calibrated. However, where this may not be practical or economic to do, the next best step is to physically check some of the electrical parameters of the device. For example, if the device has a coil inside which is used to generate a magnetic field, then a check of the resistance, inductance and insulation resistance and comparing with prior measurements will help to determine if the coil is unchanged.

Manual verification, performed by hand using multimeters and similar devices, has a number of drawbacks. As well as requiring longer downtimes, it also needs technicians to be specially trained, as well as risking further, unplanned downtime if not performed properly.

Software verification is faster, but this often entails using different software packages for different types of devices. There is also the problem that one type of verification software does not work with all communications protocols.

The best modern verification software packages can be used for many device types, comparing their settings to when they were first commissioned or calibrated and determining if their performance has degraded since that time. ABB’s Ability Verification for measurement devices software tool, has a function to allow comparison of data with both the device’s original calibration fingerprint and the results of previous tests to identify drift. A report is produced on the calibration variables, determining if the device has passed or failed on its calibrated parameters.

Making your move
Ultimately, whether a food processing operation moves towards more use of condition monitoring will depend on several factors, including the current device setup, the operating philosophy and its perception of value.

For example, not all of a plant’s many devices will be monitoring a critical process. It may be more economical to settle for reactive maintenance of these devices – they are usually very robust, with a life of some 10-20 years so there is an argument that running these less critical devices to failure is a viable philosophy. In the same plant, however, there will be other devices that really must be monitored for their health and accuracy, such as instrumentation, gas analysers or wastewater analysers used to comply with regulatory standards.

Ultimately, it will require a cost-versus-benefit analysis. Yet, with very few purely analogue devices in existence today and the increasingly rich data sets now available from digital instruments, using digital diagnostics to improve accuracy, cut maintenance costs, boost quality and productivity and ensure greater compliance to regulations makes increasing sense.

David Lincoln is Digital Lead at ABB Measurement & Analytics.


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