Risk reduction, reliability, and safety are important factors in the automated control of potentially hazardous processes such as the overpressure and containment of dangerous substances. Process Industry personnel are always aware of the need to protect people, the environment, and facilities as part of their overall risk management plan. A central strategy employed today includes safety instrumented functions (SIF), or functional safety, utilizing IEC 61511 standards. A crucial instrument in a safety instrumented system is the logic solver, which acts as a decision maker initiating the final action to make the process safe should the need arise. 
The Moore Industries STA, one of the FS FUNCTIONAL SAFETY SERIES products, is a perfect choice as a logic solver solution for use in safety instrumented architectures requiring functional safety capabilities such as High Integrity, High Availability, and 1oo2 Redundant/Voting. The STA is designed and built to IEC 61508 specifications and is third-party approved by exida® as a SIL 2 and SIL 3 capable 4-Wire (mains powered) Functional Safety Trip Alarm. It can act on potentially dangerous process conditions, provide emergency shutdown, warn of unwanted process conditions, and offers on/off control in Safety Instrumented Systems (SIS) and traditional alarm trip applications. As a bonus, comprehensive FMEDA certified safety data is available upon request for the competent functional safety practitioner to determine the STA’s applicability in a safety-related application.
Flexibility and reliability are key and Moore Industries offers two STA Functional Safety Trip Alarm solutions. The STA HLPRG input model and the STA TPRG input model. The STA HLPRG accepts current inputs from 0-50mA (4mA minimum span) or voltage inputs from 0-11V (1V minimum span). The STA TPRG supports RTD, T/C, mV, Potentiometer and Ohms as configurable inputs. Both have inputs that can be trimmed and scaled. When an alarm function and transmitter function are need for the application, both versions of the STA have an optional analog retransmission option. This Analog Output (-AO) option provides proportional and isolated analog retransmission of the input signal that can be sent to remote monitoring/control devices like a DCS, PLC, indicator or data recorder.
The STA has superior reference junction compensation (RJC) in the TPRG input model, which accepts temperature inputs. Its metal terminals and advanced electronic compensation techniques provide stable measurement in fluctuating ambient temperature conditions. The STA TPRG has advanced total sensor diagnostics for RTD inputs and performs continuous sensor diagnostics. This industry-first and patented Moore Industries feature saves time and money by letting you know when a problem occurs, its type, and location. If the RTD input breaks, the fault alarm is tripped. Plain-English error messages on the display indicates exactly which RTD wire has broken. The STA’s specific error messages eliminate the work of removing the sensor or checking all lead wires to diagnose a problem.
The STA HLPRG, mA and V input model, comes standard with 2-wire transmitter excitation that provides 24Vdc to power the loop, eliminating the need to specify and install an additional instrument power supply to power a 2-wire transmitter on the input loop. Both the STA HLPRG and the TPRG come with free Intelligent PC Configuration Software so you can set up your STA using either the external push button controls or software on your Windows PC. A major advantage to the STA is that configurations to can be performed quickly and efficiently with secure password protection. When using the software, you can download a backup copy of the configuration file onto your hard drive or removable media.
The STA can be used in many applications including a simple on/off controller. Engineered for SIS, the STA can be used to employ SIF in a variety of applications such as initiating an evacuation alarm, close a feed valve to prevent tank over flow, initiate release of fire suppressant, shutdown fuel supply to a furnace, open a valve to relieve excess pressure, or add coolant to arrest exothermic runaway.
The STA has three programmable (3PRG) contact closure alarms. One relay is factory configured as a fault alarm and the remaining two relays are user-configurable trip alarms. A dual color LED (Red/Green) indicates its condition. The fault alarm trips on a self-diagnosed failure in the STA or on any of its inputs, and the fault alarm is latching, requiring reset by the user. Only user configuration faults will clear automatically once the configuration is valid. The Trip alarms are configurable for high or low trip with an adjustable dead band.
The exida® approved SIL 2 and SIL 3 capable 4-Wire STA Functional Safety Trip Alarm can save time and money as well as provides an interface for easy configuration and quick ranging calibration as part of your SIS and traditional alarm trip solution. Organizations and safety practitioners benefit from performance, flexibility, and Moore Reliability with the STA HLPRG Programmable Current/Voltage Functional Safety Trip Alarm and the STA TPRG Programmable RTD, T/C, Ohms, mV, and Potentiometer Functional Safety Trip Alarm.
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