Electricity + Control May 2017


Intelligence and Cost Efficiency = Smart Transmitters

Jens Baar, WIKA

‘Smart transmitters’ are in a class of their own. With them, the use of the 4-20 mA output signal in process control can be exploited to the maximum. Alongside their intelligence, this new generation of instruments has the advantage of lean handling. This pays off.

M any industrial companies have established powerful Process Control Systems (PCSs) to direct their complex processes. The PCS collects the data from hundreds upon hundreds of participants or instruments in the field and carries it to powerful processors, which then execute extensive control tasks. The communication between the control systemand the end devices takes place on the basis of standardised protocols that alongside the core data such as measured values, provide increasingly more informa- tion − for example, instrument status and diagnostic information. For themanagement of data traffic in industrial processes, various fieldbus protocols have been on the rise for more than a decade. The widely used HART protocol has by nomeans been outstripped by them − HART itself continues to experience an increase in demand. Through the various integration tools for the protocols, configurations can be made directly from the PCS and information exchanged with the end devices. In addition to the DD (Device Description) and DTM (Device Type Manager), ever more frequently these are also software compo- nents that are based on the new FDT (Field Device Tool) technology. In addition to the PCS, with increasing central intelligence and ex- tensive levels of communication, the share of proven systems contin- ues to grow, which work exclusively with the long-used 4-20 mA output signal and are clearly more straightforward

implementation of a complex PCS, with respect to the cost/benefit ratio, is often not justified. With process control, along with the de- mands for increasing quality on the measurement technology to be used, cost efficiency also comes increasingly to the fore. Against this background, it is clear that both systemconceptsmust also be reflected in the sensor technology, in this case in the transmit- ters. All renowned manufacturers have suitable instruments for each type in their portfolios. Thus, at the upper end of the performance scale rank the BUS and HART transmitters, smart transmitters in the middle and the analogue instruments at the lower end. The latter are losing more and more ground as technology progresses. They are mainly being replaced by their digital ‘colleagues’ in the smart category. The advantages of this change are obvious. Smart transmitters have similar features as the high-end devices mentioned. However, despite the high quality of their measurement technology, their prices are not in the same league and are therefore far more attractive for less demanding applications. The cost advantage is primarily achieved through their design, which does not require complex firmware and consequently leads to a smaller and therefore lower-cost processor. For smart transmit- ters, as an example, manufacturer-specific protocols and the modems suited to them can be used. By using such non-standard protocols, the connection to the process

when compared to a PCS. They offer an alternative for smaller-size systems or autonomous elements of a large system in which either the complexity of the measurement and control tasks is not as extensive or the processes are less critical. In these cases, the

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Electricity+Control May ‘17


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