Field sensors functional safety

In practice, these apparatus will be selected according to the type of the sensor or actuator desired. Manufacturers offer a broad range of varying functions. The safety-related data (LZ0, I0, Por CG, L0, see Section 6.9.5) are matched to the customary values of the field devices. Sometimes, variants with different Ex i-parameters are available. 

However, it will be very important to ensure that there has been no shipping/storage/handling damage, that all sensors and final elements are correctly connected to the logic solver, that the safety instrumented functions perform properly and that the operator interface provides the necessary information. The equivalent of a proof test is strongly recommended in order to claim SIS validation, because a separate test of the logic solver and the field elements does not equal a complete end-to-end proof test. 

NOTE In the case of field devices (for example, sensors and final elements) fulfilling a given function, this function is usually identical in safety and non-safety applications, which means that the device will be performing in a similar way in both type of applications. Therefore, consideration of the performance of such devices in nonsafety applications should also be deemed to satisfy this requirement. 

F G field devices (arrangement of sensor and final element) shall be separate and independent from other devices, and used for the safety function only including activation of equipment such as fire dampers. ... 

As the title of the chapter signifies, in this part discussions will be on various components. According to the OREDA-97 report — well recognized in the world, 92% of the time these failures were due to the non-performance of their safety function upon demand by the sensors and final elements. Even if one looks from a conservative perspective as per Fig. VIII/1.0-1, at least 85% of faults are due to failed device. In modem automation systems, most of these field devices sensors and final elements are smart devices, and they are connected to the logic solvers with the help of fieldbus systems for some obvious reasons (discussed later). Naturally, these fieldbus systems need to be safe fieldbus systems. Therefore, in addition to the discussions on sensors, logic solver, and final elements, it is also necessary to address safe fieldbus systems to complete the discussions. According to lEC 61511, there are two groups considered. 

The field connections to the safety sensors and outputs are established through dedicated safety certified input/output sub systems that carry the essential diagnostics and an independent means of shutdown in aecordance with the principles we have seen. Profisafe is a certified protocol with diagnostics and fail-safe responses. The system is designed to maintain functional independence for all safety functions in hardware and software. The standard Profisafe DP protocol can then share the same network to communicate with standard controllers and standard peripheral devices such as I/O sub systems or variable speed drives. 

An effective way to ensure an accurate record of the installation checkout is to make up a composite package of data sheets and records for each field device. For example a copy of the sensor instrument specification can be clipped to the device checkout form for each safety function as shown in Figure 11.5. 

Bioactive paper has recently attracted attention as a new field with applications in global issues such as scarcity of food and water safety [137,138]. The fabrication of inexpensive bioactive packaging, assays, and sensors is urgently required for these issues. Cellulose, the most abundant biopolymer, is a superior candidate for fabrication of bioactive papers because of its biocompatibility and the accumulated knowledge about the material. Cellulose has been used as an ideal support material for bioactive systems, which utilize the pores of the cellulosic matrix to entrap biomolecules [139-143]. The internal surface of pores can be chemically modified, and the functionalized surfaces offer a high selectivity and reactivity for molecular recognition of pathogens. 

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