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Standard HMIs used to reconfigure safety control functions

23 May 2017

Using ABB’s safety PLC, standard HMIs such as control panels and mobile devices can be used to alter functional safety control functions in industrial applications.

ABB has developed a method of using standard human machine interface (HMI) products such as control panels, industrial PCs and mobile devices to reconfigure safety control functions. 
Using ABB’s AC500-S safety programmable logic controller (PLC), operators of equipment such as harbor and factory cranes, hoists, elevators, airport passenger bridges, automatic guided vehicles (AGVs), robots, mining and pulp & paper machinery can select, modify and amend their safety control functions. This allows them to achieve high functional safety standard requirements while benefiting from the convenience and low costs of using standard HMIs.

Operators of these industrial applications need to reconfigure their safety control functions to adapt to changed application conditions and to optimise machine productivity. These reconfigurations, known as safety actions, are often performed using mechanical or electro-mechanical mode selector switches connected to the digital safety inputs of a safety PLC. 
This method suffers from limited user-friendliness, inability to make modifications to switch layout and function, limited number of selection options and relatively high costs for the mode selector switches and digital safety input channels.

ABB solves these challenges by allowing standard HMIs, such as control panels, industrial PCs and mobile devices to interface with an ABB AC500-S safety PLC to carry out these safety actions.

Standard HMIs that support at least two different Ethernet based communication protocols can be used. ABB recommends Modbus/TCP and ABB ETH. A mean time between failures (MTBF) greater than 22.5 years is required for standard HMIs to satisfy PL d (ISO 13849-1) requirements. HMIs with lower MTBFs may only satisfy PL c (ISO 13849-1) requirements.
Benefits of using standard HMIs include cost savings on safety I/O channels and mode selector switches. The ability to select from a wide range of HMI products offers the user independence from any one vendor, a larger range of input options and greater flexibility to adapt the connections and layout of the HMIs.

The method allows connecting to high and low level safety systems remotely. One example is in the selection of a crane, allowing it to be controlled remotely using the emergency stop located on the operator desk. A network links the AC500-S safety PLC in the control room with the safety PLCs at the cranes. The user in the control room can select, using standard HMI equipment, which of the cranes will stop if the emergency stop button is activated on the remote operator control station. Pressing the remote emergency stop button on the operator’s desk will therefore stop the selected crane only. Independent of the remote emergency stop function, all cranes still have their own local emergency stop controls.

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