Product Details Supplier Info More products

Mitsubishi’s approach to safety relays closely integrates the standalone protection and performance of safety circuits and the diagnostic capability of the PLC.

This is achieved either by incorporation of the QS safety relay onto the PLC rack, or by direct high-speed CC-Link for the standalone networked version.

This configuration means that 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, allowing rapid identification of safety conditions on the plant.

‘This is a major step forward for plant owners and machine operators,’ said Jeremy Shinton, Q Series product manager for Mitsubishi Electric.

‘Typically, a manufacturing plant will have a number of safety circuits on it, each with it’s own standalone 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 Mitsubishi QS safety relay addresses this on two levels.

‘First, the tripped circuit is instantly identified at the control system.

‘This information can then be visualised by HMI, SCADA or simple panel indicators, which reduce the circuit search and locate time.

‘Second, a history of trips and their causes can be logged and analysed, leading to identification of recurring issues that can then be addressed.’ In developing the QS safety relay, Mitsubishi also realised that around half of all safety shutdowns are merely nuisance trips.

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 standalone 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 assessment of the overall status.

‘The QS is powered independently from the PLC,’ said Shinton.

‘If the PLC fails it does not affect the safety circuit.’ The key advantage of either integrating the QS with the PLC rack data bus, or by connecting the standalone version via CC-Link, is that detailed safety circuit status can be easily transmitted to the control system.

This feature cannot be replicated using traditional safety relays, where basic tripped status is all that can be derived.

Multiple QS relays can be included in a single PLC rack, each supporting 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 networked CC-Link version further enhances system adaptability with the ability to create small standalone groups.

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 EN ISO13849-1 standard and meets performance level E.

Mitsubishi Electric Automation Systems

View full profile