Data acquisition
EXTRACTING DATA FROM LEGACY PLANT
You want to bring your legacy plant into the 21st century by implementing comprehensive monitoring and data analysis. But there is a problem. How do you access the data you need? Fortunately, there are methods that are convenient and cost effective. Tim Dodd of ifm electronic tells all...
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f you operate or manage production plant, there are three things that you almost certainly want to do: predict machine availability by knowing if a machine is heading for a breakdown before it actually stops; improve process quality by making sure that machines are running as efficiently as they can; and optimise energy usage by keeping an eye on how much energy you are using per part or per unit volume of product.
Most of the data you need to achieve these things probably exists in your plant, but how can you get at it without spending a fortune and without upsetting the operation of the plant? This can be particularly challenging with legacy installations where, for example, sensors may only have a single 4 – 20 mA analogue output. There are, of course, expensive solutions that involve adding many extra sensors or even replacing all of the older devices, but these drastic methods may not offer a particularly good return on investment. Fortunately, there are alternatives that are more convenient and much more cost effective.
In general terms, there are four groups of solutions for accessing data from legacy plant. These are:
Hard wired, with the use of converter blocks so that overall PLC control is unaffected.
Bluetooth® mesh, which is now established as a stable and secure technology for use in industrial applications.
2G connectivity, which allows data from distant locations such as remote pumping stations to be brought back to one place.
Conventional wireless technology, using wireless routers to link into, for example, an industrial Ethernet network.
The hard-wired approach is nothing new, but there are a couple of useful details to consider. If the plant already has a fieldbus or network system, modules are available that will accept old-style analogue inputs and convert them to
digital form so that they can be connected to the fieldbus or network along with everything else. Also, replacing selected sensors with modern IO-Link smart sensors may be worthwhile. As will be discussed later, these provide much more information than their conventional counterparts. Another interesting and minimally invasive option is to use data splitters to access data that is already present in the plant but is only going to the PLC. A splitter will ensure that the PLC still receives this data, which means that it will continue to operate normally and that no reprogramming is needed. It will also make the data available for other uses, such as passing it to an ERP or data monitoring system. Yet another scenario is plants that have grown organically without the opportunity for forward planning with future requirements in mind. In this situation, accessing the extra process data the business requires can be difficult because of the location of the sensor or the machine. These could be high up or in confined spaces, as the machine has had to be fitted where space allows. The cost of the cable trays, trunking, etc.,
November 2025 Instrumentation Monthly
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