Rockwell Modernizes the Safety Relay

Rockwell Automation claims it is the global leader for machine and process discrete safety components, a market reported by IMS Research to be worth Euro631 million in Europe alone. A safety system is made up of three parts, an input device, which could be an E-stop, a light curtain, or a gate switch; then a logic element, which is where a safety relay or plc logic can be used; and then a power element, such as a safety contactor, motion system or drive. The discrete safety components cover the first two sections of such a safety system, and safety relays make up the largest section of this market, 25% of the total value, which makes a European market worth Euro150 million. IMS forecasts that market growth in terms of units sold will be 2.5% a year from 2009-2015: with a global launch and product update offering significant improvements, Rockwell is introducing a new generation of modern, simplified safety relays, presumably to maintain its position as the major supplier to this market.

The most common use of safety relays is in a hardwired configuration, with one or two safety devices feeding into the system on one zone of a machine, and around 57% of relay applications are like this. The other 43% of safety relay applications are used in more complex safety systems with three or more safety inputs and several separate safety zones. Then, as the systems become more complex, the likelihood of the user adopting a PLC-based programmable solution increases, and here Rockwell offers the SmartGuard or Compact Guardlogix solutions.

However, there is a major step involved in moving from hard-wired safety relay logic to PLC programmable control, with implications for the maintenance capability, response times and costs involved, so that there is considerable customer reluctance to change for what might be seen as the more modern approach. The U.S. magazine Control Design conducted a survey in June 2009, which Rockwell quoted, where 29.1% of the respondents said that they were using or looking at the adoption of integrated safety solutions; i.e. upgrading in technology to put standard machine motion and safety control into a plc. The real point here is that this does leave 70% of the respondents who said they were not looking at using a PLC; they were staying with hard-wired logic and safety relays. It is this part of the market that is the target for the new Rockwell Guardmaster as the next generation, offering a simpler range of safety relays, having easier connectivity, dual versatile inputs and a simple rotary switch selection of safety functions--with no customer programming.

Previously even the Rockwell safety relays were designed for a specific sensor input, such as a safety mat, a light curtain or an e-stop: The Guardmaster offers a universal input, meaning only one model works with any sensor. In fact, six models in the Guardmaster range, which includes relay expansion and time delay modules, will replace over 250 different variants of existing safety relays, leading to significant inventory savings for users. Added to this, a single 22.5 mm unit accepts a dual input, saving panel space, with a single rotary switch giving a TüV-approved concept to select the logic and reset configuration, saving on interconnection wiring time.

In another TüV-approved concept, a single wire connection between modules is used to expand and cascade multiple relays: The input from this wire can be configured with the safety inputs of the device using AND/OR logic. The capability here can be used to add a global e-stop easily wired in parallel across multiple safety zones on a more complex machine. Examples and interactive illustrations of typical wiring schemes for several applications are provided in simulation software available on the Rockwell website. Units in the new range can achieve Ple/SIL3/Cat4 to EN ISO13849-1 and IEC61508.

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