Local process diagnostics

06 December, 2022

Process control infrastructures will predominantly use programmable logic controllers (PLCs) as the main hub for instructions, process monitoring and diagnostics. In many cases, these will be connected to human-machine interfaces (HMIs) to enable an easier way to interrogate the PLC without the need for a laptop computer.

Decentralised simplicity

However, all of this equipment is usually located away from the process itself as part of a decentralised control network. As such, it doesn’t help the plant technician as he makes regular inspections of the process to immediately see any issues with components such as the control valves. What is needed is a simple and easily assessed signal or display that highlights any issues locally.

Local, at-a-glance diagnostics can take several forms. The most obvious is the use of coloured LEDs that are located in the control heads of each process valve. With normal operation indicated by a green display, it is very easy to spot any out-of-specification operation, which is clearly denoted by amber or red indicators.

For a decentralised control architecture, local valve control islands predominantly offer very little in terms of diagnostic information. This is a typical situation where plant operators would need to interrogate the PLC before they could gain any insight into any faults in the system. However, there is an alternative that can improve this situation.

Optimising operator performance

The use of coloured indicators according to NAMUR NE107 is common practice in process control applications. Bürkert and many other manufacturers have used this standard across many product lines to improve the effectiveness and efficiency of plant operators. However, improving awareness of an issue is just the first step – rectifying the situation quickly is where the most significant savings can be made.

For applications that use decentralised control, the pneumatic valve islands provide the local process management, but any diagnostics would need to be carried out at the PLC. This can extend the time to resolve any problems or complete a maintenance task.

Bürkert has taken the concept of local diagnostics to the next level with its Type 8647 and Type 8652 pneumatic valve islands by providing on-board diagnostics and messages via an LCD screen which is located on each channel. This means, for example, that a blue indicator light, which highlights a maintenance issue, can be quickly identified and resolved by reviewing the additional information provided by the LCS screen.