Balancing cost and functionality with the right logic solver

Moore Industries
Tuesday, 13 February, 2024

Balancing cost and functionality with the right logic solver

The SLA Multiloop and Multifunction Safety Logic Solver and Alarm fills the gap between single-loop logic solvers and costly Safety Programmable Logic Controllers (PLC).

The IEC 61511 Functional Safety international standard recommends the use of a functional safety lifecycle and provides guidance on the implementation of safety instrumented systems for the process industry. Central to the IEC 61511 standard lies the Safety Instrumented System (SIS), which mitigates risks to protect personnel, facilities, and the environment. Each SIS includes one or more Safety Instrumented Functions (SIFs) that help ensure safe operation. The logic solver serves as an essential element within each SIF, identifying hazardous situations and implementing measures to counteract or alleviate potential risks.

In the dynamic landscape of process engineering, there has been an escalating demand for cost-effective and compact logic solvers equipped with intrinsic voting capabilities, as a large gap exists between simplex and complex logic solvers relating to point/loop count, complexity requirements, and cost. Low point-count logic solver requirements are often handled with single loop logic solvers while larger safety systems with high point-counts are tackled with larger and costly Safety PLCs.

The SLA Multiloop and Multifunction Safety Logic Solver and Alarm from Moore Industries closes the gap between a single-loop logic solver and a Safety PLC, offering scalable safety and alarming solutions that augment existing Safety Instrumented Systems or control systems. Unlike a single-loop logic solver, which handles only one specific control function, and the pricey Safety PLC, which is designed for more complex and higher point counts, the exida certified and SIL 2/3 capable SLA strikes a balance by efficiently managing multiple control loops within a process at a reasonable cost.

When a Safety PLC is too complex or resource-intensive for just a few loops, or when a SIF needs multiple inputs for a 2oo3 voting scheme, the SLA is especially effective. It performs as a multiloop logic solver with built-in voting and enhanced maths capability typically found in Safety PLCs. The SLA can handle everything from simple alarming to more complex schemes that include 1oo2, 2oo3 or even 5oo8 voting architectures, enabling it to act on hazardous risk mitigation; warn of unwanted process conditions; provide emergency shutdown; or provide on/off control in Safety Instrumented Systems and traditional alarm trip applications.

The SLA accepts up to four discrete and six analog inputs from a wide array of devices and sensors. HART data from connected field devices can pass through the SLA to its analog outputs enabling connected hosts and asset managers bidirectional communication for continuous monitoring and programming. Its four relay outputs and up to four discrete contact closure outputs can be driven by any of 16 internally configured alarms, where individual or multiple alarms can be assigned to each relay or discrete output. Relay and discrete outputs can also be triggered by any input or internal diagnostic fault. Three optional analog outputs allow the transmission of any input or internally calculated equation or variable.

With user-configured security jumpers to ensure secure digital communication and prevent unauthorised programming, the SLA is easily configured with any FDT-compliant host utilising the SLA’s DTM with simple drop-down menus and checkboxes. No custom or licensed software is required. This ease-of-use functionality includes a powerful equation editor that the user can employ to create monitoring, alarming, and control schemes involving simple to complex equations using timers, running min/max functions, prebuilt analog and discrete logic functions, and more.

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