Digital actuator solutions benefit the bottom line
April 1st 2007

In this article for Water, Energy and Environment magazine, Ian Sully, UK managing director for AUMA observes that, when it comes to the automation of processes in industrial environments, fieldbus systems are being increasingly adopted.He notes that the trend towards fieldbus technology for actuation solutions has been heavily influenced by the considerable cost savings that can be made in planning and commissioning, as well as operation and maintenance

irst introduced in the early 90s, digital technology provided a new level of sophistication for actuators which had already established their role over the preceding 100 years providing front end 'intelligence'for valve operation in industrial plant applications including the water and energy markets.

New generation bus systems have removed the need for hard wiring and presented a simpler and more effective option which offers many benefits, including cost savings.

Traditionally,a 20-core multi cable has been connected to each actuator at the plant.However, with the fieldbus option, a simple two-core cable is used resulting in substantially less cabling which is reflected in significant cost reductions.And, with just two wires instead of 20,commissioning becomes considerably easier with less chance of wiring errors.

A fieldbus is an industrial communication system connecting a variety of field devices such as transducers (sensors),motor operated valves (MOVs) and actuators (drives) to a control system.Fieldbus technology was developed in the 1990s to replace parallel wiring of binary signals which was common at that time.

At least one control system, and often several transducers and MOVs, are required to control a process. If the process is to be performed electronically, the question is how the transducers and MOVs should be connected to the control system.

There are two basic ways to achieve this – the first option is to establish a separate signal channel from the control system to each transducer.

The second approach is to implement the signal exchange between the control system and several transducers and/or MOVs via a two wire cable (serial wiring).

The higher the level of automation of a plant or machine, the larger the number of cables for parallel wiring due to the increased number of input and outputs: implementation, installation, commissioning and maintenance become both time consuming and costly.The demands placed on the cables are often high e.g. special cables have to be used for the transmission of analogue values. Parallel wiring therefore becomes an essential cost and time factor in the automation of technology. In comparison, serial wiring on the field level eliminates the cabling complexity leading to dramatic cost savings.

The fieldbus replaces parallel trunk groups by a single bus cable and connects all devices from field to process controller.Whatever the automation device, the bus solution links all devices in the field via a simple two core cable.

Bus technology substantially increases the potential for feedback of process information and provides a powerful communication solution.

Based on the successful uptake of digital technology there are a number of different systems with different characteristics adopted today including Profibus, Interbus and ControlNet.The strongest interest to date has been shown in Profibus as it is recognised as a particularly userfriendly option that controls a comprehensive range of field devices.

Reaping the rewards of fieldbus: The cost savings associated with adoption of fieldbus technology include significantly reduced spend on wiring as a single twisted pair of cables replaces the complex installation, and maintenance, of large numbers of cables.

By eliminating cabling, there are also savings in capital expenditure.

Additionally, by reducing the complexity of cabling, associated plant design and planning costs are reduced.Cost saving rewards from fieldbus are also reaped from longer term reliability which is a key benefit of system simplification."

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