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Minimising whole life costs starts with product selection

Minimising whole life costs starts with product selection

New analysis into control systems shows that you can reduce costs by managing sensors and transducers more effectively.

The first areas that instinctively spring to mind when an engineer is challenged to reduce costs are usually purchase cost and installation. Why not? They are the obvious ones and they are the easiest to define and list. When viewed as part of a system however, purchase cost plays only a small part; managing the multiple signals from sensors and transducers differently can radically affect the total cost of ownership for that process system.

Careful analysis conducted by Volker Erbe, sensors product manager at Bürkert Fluid Control Systems investigating the whole life costs associated with field devices such as sensors, transducers and the control platform they are connected to, has revealed there could be far larger savings to be had from making changes to product selection at the initial stage of a project - changes that can have huge cost repercussions that occur during the less obvious operational phase, those such as training, start-up, process operator time, service, repairs and documentation.

Volker carried out the research to help define costs more accurately for Bürkert field devices; he then identified where costs lie within a whole life application and quantified the results of making better decisions early on in a project. The initial question Erbe started with was: What part do field devices play and what proportion of the cost associated with them can be saved?

"The quantity of field devices in  applications is increasing almost exponentially," he says, "based on a higher level of automation. Figures show that in a typical food, pharma or general industry application, about 20% of the overall investment costs are for sensor based measurement devices and up to 75% of the TCO are costs in the operational phase which we estimated at 15 years usage time."

Overall process control costs and the possible cost reduction potential is of course dependent on variables within individual plant set-up including the size in terms of I/O, building size, distances and the kind and complexity of processes and sub processes involved. Environmental conditions such as high temperatures, high pressures and the kind of media - for example aggressive, dangerous or difficult fluids or gasses of any kind - plus other special conditions such as security demands, standardisation and norms, plus certificates all play a part. In addition there are often key local priorities, conditions and resources such as education and the level of redundancy required to be considered.

"In each of the different areas of cost, however, there is a potential for cost reduction," says Erbe. "We concentrated on the effects in relation to a control loop, linking sensors and transducers (flow, temperature, level, pH) in a measurement and control (eg PID) loop with positioners and valves. We ran several simulations and also drew data from a range of real applications in order to reach trustworthy medians in terms of cost."

Analysis of initial costs
Planning is a cost which almost always justifies the investment, as does any time taken to specify instruments and equipment. Purchasing has an administrative cost associated with it and Erbe found that, remarkably, the equipment itself only accounted for around 17% of the initial cost - less than the cost of training when dealing with new equipment.

Other items Erbe took into consideration included support from both internal and external sources, installation - both mechanical and electrical, including wiring of all external hardware for comms and power - plus commissioning and start-up costs including all necessary documentation for plant, instruments and wiring.

"It is not until you reach this level of analysis that you start to see a pattern forming in the peripheral activities, and then start to appreciate the hidden costs," comments Erbe. "Only then do you begin looking to specify a solution that reduces indirect costs, knowing that the saving can be significant when compared to the initial purchase cost of the devices themselves."

Erbe then looked at operational costs. "We defined these as recurring activities, including on-going hardware and software management, production monitoring and control, maintenance, service and repair, any enhancement carried out during the life of the product, additional documentation, and then finally decommissioning including recycling costs," he says. "To be totally accurate you have to analyse your own plant to have a base line which gives you information about the share of operating costs, identifying which area is of interest for achieving the best results in cost reductions. You can however use our broad analysis to draw some obvious conclusions."

In order to show savings in operational terms, the flexibility of a product is vital, as is its modularity in terms of hardware and software. Sensors and transducers have a fixed operational envelope, and also a minimal price differential between manufacturers of reliable quality products. The controllers they are connected to however can affect costs dramatically.

Each product should ideally have a wide range of usage, this leads to device consolidation and a reduced number of different products in use, this can then generate a virtuous circle which requires reduced training effort, allows more flexible staffing and reduced effort in all production processes as well as managing the products in use.

So how does a field instrument support cost reductions in practice? The simple answer is to specify the right one in the first place. The handling of a product, for example, must be easy and repeatable. This typically means no specialist tools required for installation or commissioning, hence no hidden costs and no need to carry large amounts of kit in order to have a wide range of tools to hand.

Data management should be easy, and Erbe realised that simple things such as the upload and download of settings, cross referenced with data storage capacity and easy configurability of multiple items, made a huge difference to the end user. "A more intelligent field device needn't mean a more complex one to handle, because that would likely negate any cost saving in process."

All this research was taken into account in the design of Bürkert's multiCELL 8619 compact field based process controller. This meant investing in multiple interchangeable control boards for pH, conductivity, inputs and outputs, plenty of on-board intelligence with intuitive menus and parameter settings, plus set programs for controlling a variety of analogue and digital process signals via a simple menu structure that included text and icons, all displayed on a large, clear, backlit screen that could be easily interacted with in a process environment.

Erbe firmly believes that there are substantial cost savings to be made from the complete lifecycle of a product such as a multi-transmitter/controller, that cost reduction starts with device selection and savings are made both directly and indirectly. Each individual plant needs to carry out some analysis based on its own individual instrument usage, the kind of processes taking place and the individual operating conditions.

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