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Mitsubishi faces energy and safety demands

24 October 2008

Safety and energy efficiency were the key words on Mitsubishi’s lips as they launched a range of inverters and safety relays. The D700 inverter range is claimed to be powerful despite its small size. The company also says that its safety relays integrate protection and performance of safety circuits with diagnostic capabilities of PLCs.

The D700 range is promoted as a ‘micro’ drive, as the inverter itself is physically small, with Mitsubishi claiming that certain drives within the range have nearly 60 per cent less volume than their high performance predecessors. The new drive also integrates with other ‘micro’ products from Mitsubishi, such as the compact FX3UC programmable logic controller and the GT1020 operator interface. It covers 0.4kW to 7.5kW three phase, and 0.1kW to 2.2kW single phase.

The D700 uses sensorless vector control and advanced energy optimisation algorithm to constantly adjust its settings to meet the changing load requirements of the application.

Guy Kennett, drives manager of Mitsubishi, said: ‘We now have a single drive product that will cover all applications, from pumps and fans to conveyors and hoists.’

Mitsubishi has tackled energy consumption with intelligent threshold control for a situation where the drive is running with no operational output; such as a pump running at minimum speed with no real flow requirement, or a conveyor system which is running but totally unloaded for a period of time. The drive can stop the motor and be ready to come back to speed using a fast algorithm to negate any demand dwell.

The company has also added a safety stop within the drive, which stops and safely removes the power from the output. The drive can be fed directly by the system safety network removing the need for separate contactors to break the mains connection in the event of an emergency.

For operational safety, the D700 predicts the life of major components within the drive so that maintenance can be planned and action taken rather than unscheduled stoppage. The D700 actively monitors its own functional operation and safety, such as initiating a warning if the cooling fan becomes erratic, monitoring the major components such as capacitors and semiconductors for age and operational usage to give a predictive life expectancy.

Mitsubishi claims that downtime and safety are inextricably lined, saying a common cause of costly operational downtime can be traced to the operation and resetting of traditional stand-alone safety circuits.

The company said it closely integrates the stand alone protection and performance of safety circuits and the diagnostic capability of the PLC either by incorporation of the new QS safety relay onto the PLC rack, or by direct high speed CC-Link for the stand alone networked version. This configuration means that for the first time, detailed intelligence is instantly available on the operational condition of the safety relay as well as the status of each of the connected safety circuits, thereby allowing rapid identification of safety conditions on the plant.

Jeremy Shinton, Q Series product manager for Mitsubishi Electric, said: ‘Typically a manufacturing plant will have a number of safety circuits on it, each with its own stand alone safety relay protecting one particular aspect of the process. If one of these circuits trip, the whole plant may be effectively shut down and production lost while engineers inspect the machine or process line looking for the appropriate relay and circuit to identify its cause and correcting the reason before restarting operations.

‘The New Mitsubishi intelligent QS Safety Relay addresses this on two levels. Firstly the tripped circuit is instantly identified at the control system. This information can then be visualised by HMI, SCADA or simple panel indicators which dramatically reduce the circuit search and locate time. Secondly a history of trips and their causes can be logged and analysed, leading to identification of recurring issues which can thus be addressed.’

In developing the QS Safety Relay, Mitsubishi also realised the importance of the fact that something like half of all safety shutdowns are merely nuisance trips – typically someone brushing against an E-stop or a light curtain being broken by a badly wielded broom. Each inadvertent stoppage adversely affects productivity and impacts the bottom line of the host business.

The QS Safety relay sits on the rack of Mitsubishi’s Q series PLC and integrates fully with the plant or machine’s functional control system. The stand-alone version is connected over CC-Link to the host PLC system. Data from these relays may be linked into higher level control systems such as MES (manufacturing enterprise systems), SCADA (supervisory control and data acquisition) and various management information generating systems.

The QS monitors eight variables per connected safety circuit, safety input status (on/off), safety output status (on/off), safety relay coil status (on/off), and safety relay contact status (on/off). The various possible combinations of these are the basis of a strong diagnostic capability developed from the control system’s intelligent assessment of the overall status.

Shinton said: ‘Most importantly the QS is powered independently from the PLC.

‘So if the PLC fails it does not affect the safety circuit, this stays independent protecting man and machine come what may.’

By integrating the QS with the PLC rack data bus, or by connecting the stand-alone version via CC Link, detailed safety circuit status can be easily transmitted to the control system.

Multiple QS relays can be included in a single PLC rack, each of which can support up to three extension relays, connecting directly to individual field devices such as drives, switches, light curtains, interlocks and temperature monitors. Networking of PLCs effectively allows large safety systems to be configured.

The CC Link version also supports up to three extension relays and multiple CC relay stations can be configured. The flexibility of this architecture allows the safety circuits to be ‘zoned’ so that a safety trip only shuts down the relevant part of the plant. The QS is certified by TUV, and covers EN954-1, Category 3 and Category 4 installations. It has also been certified to the new EN ISO13849-1 standard and meets performance level “e”.


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