Buyers Guide 2021

14 | Plant & Works Engineering www.pwemag.co.uk Annual Buyers’ Guide 2021 Insight Condition monitoring for process instrumentation Plants such as water treatment facilities and food and beverage factories rely on a large range of process instrumentation – quite obviously, without accurate readings of parameters such as flow rates, pressures and temperatures, their operations would grind to a rapid halt. PWE reports. D evices such as flow meters and pressure transmitters perform this vital work, 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? Today’s process instrumentation is largely digitally based. As such they produce a wealth of 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. In the past, many plant operators took a reactive approach, where a device was allowed to break and then was fixed. This is an expensive which could lead to the whole plant tripping out, extended down time and a rush to find replacement parts or devices. In a batch production environment, such as mixing orange juice concentrate with liquid, the failure of a flow meter would not allow the right proportions to be mixed to produce the correct quality of product, stalling production. In a petrochemical process, based on 24/7 continuous production, allowing a temperature transmitter to simply fail could be potentially catastrophic. In the 1970s to 80s, preventive maintenance came to the fore, with devices maintained to a schedule. This was highly manual, with equipment being checked by staff walking the line to note which devices were reading or behaving as expected and which ones needed attention. Over the last few years, the concept of predictive maintenance has become ever more popular, with the aim of trying to prevent failure events. Although predictive maintenance is still a form of preventive maintenance, it uses actual condition-based data to determine when to perform maintenance, as opposed to a pre- determined schedule based on historical information. Condition monitoring of equipment allows us to schedule maintenance and prepare for it in advance, for example, ordering spare parts. We can also make use of the increasingly rich data available from measurement devices to identify exactly what went wrong and derive strategies or techniques to prevent the same problems occurring in the future. There are two main reasons for condition monitoring. The first and most obvious is that we want to check the device’s health to ensure process and product quality, the second is ensuring that processes remain in a safe condition. Using the data So how can measurement device users begin to take advantage of these capabilities? At a very basic level, it comes down to how we communicate with the device. Although most measurement devices are digital, many applications continue to use the tried and tested 4-20mA current loop rather than digital communications networks. For example, if 4-20mA measurement devices also offer HART communications, a bi- directional communication protocol that provides data access between intelligent field instruments and host systems. The communications link carries the process values, like flow rates or temperature. It also gives access to the device’s diagnostics data, such as its operational status. Many advanced digitally enabled measurement devices will offer sensor checks including internal connections, an indication of sensor memory failure and an internal electronics check. With communications in place, device interrogation is the next step. There are two