Research On The Design Of Functional Safety Safety Barriers Based On IEC61508

With the development of industry, complexity of process units keeps increasing day by day, and it has become one of the research hotspots that how to guarantee the safety. Functional safety has brought a new design method of safety instrument systems, which makes the design of safety systems based on fault become a kind of design based on functions. IEC61508standard comes into existence, which brings a specification for functional safety.In this paper, functional safety’s general situation of development is researched, including the development of functional safety standards and the development of functional safety product. This paper briefly introduces the basic content of the functional safety primary standard IEC61508, and presents the basic function requirements and functional safety requirements of functional safety safety barriers, that is receiving signal of RTD and TC, converting the signal into4-20mA and outputting. The safety barrier in this paper has SIL2, single channel1oo1D, and its SFF is in the range of90%-99%, PFD is in the range of10-7～10-3.This paper designs the safety barrier from the aspect of hardware and software. In the design of the hardware, how to achieve the safety barrier’s function is been decided, all kinds of chips are selected, and the design of every module’s circuit is completed. Use24bit high precision AD converter to sample signals. Use MSP430MCUs to process data, and the result is output in the form of PWM wave, then the PWM wave converts into analog signal by filter circuit, and the final current value is got. In the design of the software, use C language to code in the MCUs. The programme accomplishes sampling voltage value turns into the temperature value, then to the current value, and at last to the PWM code. Besides, according to the circuit, coding completes the MCUs’self-diagnostics and the monitoring of other main functions.At last, the failure rates of every component, every module and the whole safety barrier are analyzed by FMEDA, including safe failure rates, diagnostic dangerous failure rates and undiagnosable dangerous failure rates. According to these, SFF and PFD can be calculated, and within certain proof test interval the final design result meets the requirements of SIL2.