Safety controller configured without software

Paul Boughton

Five years ago, relays were the only practical option for safety controls on machines, but recent technical advances have seen the development of numerous software-based safety-related controllers.

Despite these new systems, relays still have around 80 per cent of the market share; the basic fact remains that relays are a scalable way to implement almost all industrial safety-related control systems.

However, many safety relay applications require customers to undertake hours of tedious wiring in order to implement the particular safety logic needed for their application. Customers often endure these wiring challenges rather than using proprietary firmware-based safety-rated controllers that require software for configuration and may not support the necessary scalability of the application.

Sick has overcome the problems of complex wiring and the need for proprietary software with its new UE 410 Flexi Modular Safety Controller, a series of modular units that allows users to implement complex safety-rated logic without the use of software. The logic functionality within the UE410 Flexi series is easily implemented by using simple rotary switches on the front of each module.

The UE410 Flexi series comprises a number of units - a main control unit, an expansion (extension) control unit, an eight dual-channel safety input module, a one-dual-channel safety relay output module (two normally-open and one normally-closed contact), a two-dual-channel safety relay output module (four normally-open and two normally-closed contacts), a Devicenet interface module and a Profibus interface module.

Modules can be combined with one another to create a bespoke safety logic system specific to the user's application, using the interface connections on the side of each unit. A combination of up to 104 inputs and outputs can be supported, while the fieldbus network communication modules can be used to provide diagnostic information for the plant-wide system.

Until now, users have needed different safety relays for different safety systems such as: two-hand control applications; contact-based safety outputs such as safety interlock switches; semiconductor-based safety outputs from light curtains or laser scanners; and emergency stop applications. Addressing this complexity overhead, the UE410-Flexi can handle all of these devices and, using the modules, combine them logically, thanks to eight possible settings on each module.

Another benefit the UE410-Flexi offers is that the number of different relays needed for a particular application is drastically reduced - saving on spares and panel space. Devices that can connect to the UE410-Flexi include: emergency stop pushbuttons, Type IIIA and IIIC two-hand controls, safety interlock switches, non-contact switches, testable Type 2 sensors, hold-to-run (enable) switches, safety light curtains and safety light grids, safety laser scanners and muting sensors for two-input muting.

To assist users with selecting the correct settings for the switches on the modules, Sick has developed a software tool that can be downloaded for free from its website. For each switch setting, the tool shows what the module's functions are, enabling a schematic of the safety circuit to be compiled - including the safety devices on the machine.

For more complex machinery, expansion units can be used to create separate safety zones so that, for example, breaching a light curtain on a palletiser at one end of the machine will not halt the infeed conveyor at the far end.

The system is designed to meet the requirements of safety circuits for Category 2, 3 or 4 machines as described in BS EN 954-1 or SIL 1, 2 or 3 of BS EN (IEC) 61508 or BS EN (IEC) 62061. Logic blocks are accessed by selecting pre-configured functions using the program switches, therefore the typical wiring used to achieve this logic disappears. For example: the UE410-8 dual-channel safety input module can take four dual channel inputs and combine them with the inputs on a UE410-Flexi main control unit using AND, OR, or Bypass logic. All that is required is connection of the monitored devices and setting the program switches. To implement a similar logic scheme using safety relays, ten or more relays would be necessary.

Once this logic has been implemented, semiconductor outputs located on the main control unit can be used to switch off the dangerous motion. Easy implementation of relay outputs can be achieve using the one and two dual-channel safety relay output module

For diagnostic information, each module has LEDs that indicate the state of the associated inputs and outputs as well as fault conditions and reset requirements. Additionally, the Devicenet and the Profibus modules can be used to deliver a wide range of status and diagnosis information.

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