Bus technology moves into the panel
13 March 2012
A Frost & Sullivan report highlights the convergence of PLC's but states that this is a technical strategy that has yet to demonstrate it can yield results. Stuart Greenwood of Eaton's Electrical Sector argues that this trend is already advanced and is delivering results.
It could be claimed that as soon as remote I/O modules became available, the process of convergence between PLC's and DCS's got underway so it is not really a ‘new trend’. However, this convergence is continuing to spread and most modern automation systems now incorporate intelligent devices in the field.
With these devices linked to the central controller via a network or fieldbus connections, it seems meaningless to distinguish between the PLC and the remainder of the automation system. The exception to this rule is within the control panel because, although conventional hard wiring of field devices has virtually disappeared in all but the smallest of installations, traditional hard wiring is still very much the norm inside the control panel.
Of course, the wiring runs are shorter inside the panel than outside, but that is no longer a valid reason to ignore the benefits that bus-based panel wiring can provide and this is now addressed with bus-based lean panel wiring systems, such as the SmartWire-DT from Eaton's Electrical sector.
This system allows all devices within a control panel - such as motor starters, HMI panels and even conventional pushbuttons and indicator lights - to be connected to the central controller via a daisy-chain, eliminating the need for conventional control wiring.
Cutting wiring time
Some of the benefits of this are instantly apparent. It dramatically cuts panel wiring time, as it almost eliminates the possibility of wiring error. The time needed to test panels is also reduced, as is the risk of problems during commissioning. Modifications to the panel can also be made more easily - instead of having to carry out extensive wiring changes for even the simplest modification, all that is needed is to daisy chain the new components to those already there.
The biggest benefit, however, must be that the use of lean panel wiring facilitates the flow of information between components mounted in the panel. A suitably equipped motor starter could, for example, report the running current of the motor and the status of the protection device to the central controller, where the information can be processed and used to initiate further actions, such as sending a message to the HMI panel alerting the operator to an impending overload condition before a trip occurs.
So, adopting lean panel wiring improves the transparency of the automation system. Since fieldbus- and network-based field wiring already supports information exchange, the addition of lean panel wiring means that any information about any aspect of the automation system’s operation and status can be made available wherever it is needed and it is this transparency that is one of the key elements needed for ‘lean’ automation.
Lean manufacturing is a well-known concept based on identifying sources of waste and inefficiency in a process and eliminating them. Lean automation extends this concept to automation systems, slimming down control panels, simplifying wiring, increasing data transparency and enhancing performance while reducing overall costs. The introduction of lean panel wiring allow lean automation to cover the entire manufacturing process - from the ERP system down to an emergency stop button.
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