Instrumentation system design

Which measurements need to be taken to detect the onset of the hazardous conditions. A simple example could be that a pressure rise above a specified vaiue needs to be detected. The value of the parameter at which action shouid be taken wiii need to be outside the normal operating range and less than the value that will result in the hazardous condition. An allowance will need to be made for the response of the system and the accuracy of measurement. In setting the limit, there will therefore need to be a discussion with those responsible for the safety instrumentation system design and implementation. 

This annex references a number of techniques for caicuiating the probabilities of failure for a safety instrumented system designed and instaiied in accordance with lEC 61511-1 ANSI/ISA-... 

Classification of SIF for the triggered safeguards out of risk matrix (Table 3.2) should be designed to comply with the risk target set by the company/local codes. The next section covers the methodology of Safety Instrumented System design... 

The lEC 61508 safety lifecycle prescribes that planning for all maintenance testing and maintenance activities must be accomplished in the realization phase. To a certain extent this work can proceed in parallel with safety instrumented system design. This lifecycle diagram also shows that operation and maintenance responsibilities focus on periodic testing and inspection as well as management of modifications, retrofits, and eventual decommissioning. 

Another difference between Basic Process Control System design and Safety Instrumented System design is that per ANSl/lSA-84.00.01-2004 (lEC 61511 Mod) these systems are designed and implemented to meet different risk reduction requirements presented by the various hazards. (Chapter 1)... 

Current functional safety standards, lEC 61508 and ANSl/lSA-84.00.01-2004 (lEC 61511 Mod), (Ref. 1 and 2) state that probabilistic evaluation using failure rate data be done only for random failures. To reduce the chance of systematic failures, the standards include a series of "design rules" in the form of specific requirements. These requirements state that the safety instrumented system designer must check a wide range of things in order to detect and ehcninate systematic failures. 

There are advantages in safety instrumented system design to choosing a pre-designed matted set of actuator and valve. A correct combination of actuator and valve will match characteristics of each to provide the best optimization of fail-safe characteristics. 

Many instrumentation systems and control devices require power sources, electrical or pneumatic, which have to be reticulated around the plant. The cost of instrument air is routinely underestimated, mainly because the associated piping costs are not appreciated when the P I diagrams are drawn up, but also because of a disinclination on the part of the instrument system designers to make any compromise on air-quality requirements. Even a few parts-per-million of oil may be regarded as unacceptable, with consequent cost increase to the air compressor. Both instrument power supplies and instrument air have to be provided in an adequately secure fashion in relation to the consequences of their failure. 

The standard applicable for application software, has limited variability or fixed programmed but not for manufacturers, safety instrumented systems designers, integrators, and users that develop embedded software. 

For certification of the products, tools like FMEDA and Markov models are used. An FMEDA extends the FMEA techniques to include online diagnostic techniques and identify failure modes relevant to safety-instrumented system design. These PFD calculations may be carried out by commercial software tools (e.g., SILence by HIMA). In all these cases, bottom-up approaches were undertaken. Also it has been found tbat there has been a serious lack of reliable failure rate data and their variations among lab specifications, lab/field and field specifications. There are wide variations in the data obtained from these different sources. Therefore it is suggestive to use a band of data instead of discrete PFD and other failure rate data [5]. 

Gruhn P, Cheddie HL. Safety instrumented systems design, analysis, and justification. 2nd ed. Research Triangle Park, NC ISA 2006. 

Gruhn, P., Cheddie, H., Safety Instrumented Systems Design, Analysis, and Justification, The Instrumentation, Systems, and Automation Society, Research Triangle Park, North Carolina, 2006. 

The safety instrumented system design proceeds on the basis of a safety requirements specification that has also been aligned with the detailed HAZOP study. 

Unfortunately, there are so many variables in the optical path of any fluorimeter, or any other spectrometer system, that such systems simply do not exist and it is for this reason that careful consideration to instrumental system design, calibration, and correction methodologies is essential. 

Operation When operated correctly, thickeners require a minimum of attention and, if the feed characteristics do not change radically, can be expected to maintain design performance consistently. In this regard, it is usually desirable to monitor feed and underflow rates and sonds concentrations, flocculant dosage rate, and pulp interface level, preferably with dependable instrumentation systems. Process variations are then easily handled by changing the principal operating controls—underflow rate and floccirlant dose—to maintain stability. 

Instrumentation (Arthur D. Little, Inc., and Levine, 1986.) Instrument systems are an essential part of the safe design and operation of systems for storing and handling highly toxic hazardous materials. They are key elements of systems to eliminate the threat of conditions that could result in loss of containment. They are also used for early detection of releases so that mitigating ac tion can be taken before these releases result in serious effects on people in the plant or in the public sector, or on the environment. 

Design equipment to accommodate maximum operating envelope. Appropriate use of Safety-Related Systems (SRS) such as Safety-Instrumented Systems (SIS). 

Minimize the effect of electrical interference by the design, installation and selection of instrumented systems... 

Eisher, T. G. 1990. Batch Control Systems—Design, Application, and Implementation. Instrument Society of America. 

Control system design engineer modern plants contain sophisticated control and trip systems and HAZOPs often result in the addition of yet more instrumentation. 

These last three are special valves from the viewpoint of chemical and petrochemical plant applications, but they can be designed by the major manufacturers and instrumentation manufacturers as these are associated with instrumentation controls. Care must be taken in the system design to make certain it meets all ASME code requirements. 

For final design horsepower and equipment selection, the usual practice is to submit the refrigeration load and utility conditions/requirements to a reputable refrigerant system designer/manufacturer and obtain a warranted system with equipment and instrumentation design and specifications including the important materials of construction. Always request detailed operating instructions/controls and utility quantity requirements. 

In the next section of this chapter, we will review a variety of instrumentation approaches to the FLIM experiment. In particular, we describe conventional systems as well as those designed to observe variation in a, and systems designed for the collection of multifrequency data. In this context, we will also look at data collection strategies and the subsequent first pass analysis of the acquired... 

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