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Selection Criteria
Selection Tips
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Is This a Multizone Application?
In order to comply with safety standards and remain productive, machine builders have begun building functional safety features into machines using what has been termed the “Zone Concept.” The Zone Concept increases both safety and productivity by allowing a portion of the production line to slow or stop while the rest of the line remains active. The safety hazard, whether a minor malfunction of line equipment or an obstruction, can be removed or corrected without taking the entire line down, eliminating lengthy production shut downs and worker downtime. When the hazard is cleared, the line can quickly return to normal operation. Single function and/or expandable relays systems are suited only for single-zone control, while multizone control for 2…3 zones is best served through a configurable system such as MSR300 relays or a SmartGuard packaged controller. Any applications involving control of more than three zones (and therefore more complex logic) is better suited for a programmable safety controller—SmartGuard, GuardPLC or GuardLogix.
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Diverse Inputs—Number and Type
For single- and multizone applications (£ 3 zones), the number and type of inputs (e.g. interlock switches, safety mats, light curtains) will dictate the use of either safety relays (MSR100, MSR200 and MSR300) or a small packaged safety controller such as SmartGuard. For 1…2 inputs, dedicated standalone relays (MSR100) are a simple and cost effective solution, but for applications involving a high number of input devices, the hard wiring associated with individual relays can be restrictive. Therefore, in applications requiring a moderate input device count (20 or less), an expandable relay system with modular design and plug-in connections (MSR200, MSR300) is an ideal solution. In any case with safety relays, the types of input devices used will dictate the relay modules that must be selected; thus relay selection for a wide range of input devices can be complex. Applications requiring greater than 20 diverse inputs and a degree of complex logic lend themselves to the SmartGuard Controller in combination with Distributed I/O. Larger installations—those with a high number and wide variety of input device types—are best served with a safety PLC system as their programmable nature allows safety applications to be solved in software rather than hard-wiring large, cascaded relay systems.
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Is Standard Control Using a Logix Controller?
A safety control system can be a dedicated (safety only) system or integrated, where standard and safety control are combined to maximize the re-use of components and tools.
GuardLogix brings together the benefits of a Logix platform—common programming environment, common networks, and common control engine—with integrated safety control in an easy-to-use environment while providing Safety Integrity Level (SIL) 3 control. By partnering with the Logix5000™ processor, GuardLogix users can benefit from common programming software, controller and I/O to help reduce development time and application cost.
GuardPLC and SmartGuard are the recommended platforms for applications requiring safety to be physically separated from standard control.
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Do You Need Communications?
On-board communications allow the relay to deliver output and error status over an RS232/RS485 or fieldbus network (such as DeviceNet) to an HMI or other device. While the MSR200 series of modular safety relays does offer communications compatibility, it is not the most economical solution—MSR300 configurable safety relays are the best choice for applications requiring communications. Programmable safety controllers offer network connectivity and a high level of diagnostics, with SmartGuard and GuardPLC having DeviceNet and Ethernet capabilities, respectively.
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Do You Need Muting?
Sometimes the process requires that the machine stop when personnel enters the area, yet remains running when automatically-fed material enters or exits—this is a situation where a muting function is necessary. Muting requires the combination of a light curtain, two or four muting sensors and a control unit to process the signals and determine if and when to activate the muting function. Muting sensors are mounted in front of and behind the light curtain and only a specific sequence of sensor outputs will initiate the muting function. For example, when the two sensors in front of the light curtain change state within a predetermined timeframe, the light curtain is “muted” and will not send a stop signal to the machine as the material enters. The MSR300 modular safety monitoring relay offering includes a module specifically designed to control the muting function in applications that do not require a specific sequence or timing requirement. Muting of the MSR42 can be conveniently set up using configuration software. If sequence and timing is required, then the MSR22LM may be better suited for your application.