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Glossary Term: Resealing pressure
The inlet pressure at which fluid no longer leaks past a relief valve after it is closed.
Glossary Term: Repeater
1. Device used to extend the range over which signals can be correctly transmitted and received for a given medium. 2. A device that amplifies or regenerates data signals in order to extend the distance between data stations.
Glossary Term: Repeatability
The ability of a transducer to reproduce output readings when the same input value is applied to it consecutively under the same conditions, and in the same direction. NOTE(S): Repeatability is expressed as the maximum difference between output readings; it is expressed as “within percent of full- scale output.” Two…
Glossary Term: Relief valve
An automatic pressure relieving device actuated by the pressure upstream of the valve and characterized by opening pop action with further increase in lift with an increase in pressure over popping pressure. See pressure relief device.
Glossary Term: Reliability block diagram
Probability combination method for estimating complex probabilities. Since it generally takes the “success” view of a system, it can be confusing when used in multiple failure mode modeling.
Glossary Term: Reliability
1. The probability that a device will perform its objective adequately, for the period of time specified, under the operating conditions specified. 2. The probability that a component, piece of equipment or system will perform its intended function for a specified period of time, usually operating hours, without requiring corrective…
Glossary Term: Redundancy
Use of multiple elements or systems to perform the same function. Redundancy can be implemented by identical elements (identical redundancy) or by diverse elements (diverse redundancy). Redundancy of primarily used to improve reliability or availability.
Glossary Term: Receptor
The object or persons on the receiving end of the harm in an unwanted event. Common receptors include personnel, plant equipment, plant production, the environment, and the general public.
Glossary Term: Ratio controller
1. A controller that maintains a predetermined ratio between two or more variables. 2. Maintains the magnitude of a controlled variable at a fixed ratio to another variable.
Glossary Term: Rated capacity
The manufacturers stated capacity rating for mechanical equipment, for instance, the maximum continuous capacity in pounds of steam per hour for which a boiler is designed.
Glossary Term: Random failure
A failure occurring at a random time, which results from one or more degradation mechanisms. Random failures can be effectively predicted with statistics and are the basis for the probability of failure on demand based calculations requirements for safety integrity level. See systematic failure.
Glossary Term: Quick-opening valve
Control valve with trim characteristic designed to produce large flow capacity with small amount of valve opening.
Glossary Term: Pyrometer
Any of a broad class of temperature measuring instruments or devices. Some typical pyrometers include thermocouples, radiation pyrometers, resistance pyrometers and thermistors, but usually not thermometers. It is a temperature transducer that measures temperatures by the EM radiation emitted by an object, which is a function of the temperature.
Glossary Term: Purging
1. The addition of air or inert gas (such as nitrogen) into the enclosure around the electrical equipment at sufficient flow to remove any hazardous vapors present and sufficient pressure to prevent their re entry. 2. Elimination of an undesirable gas or material from an enclosure by means of displacing…
Glossary Term: PTI or TI
Proof Test Interval - The time interval between servicing of the equipment.
Glossary Term: PTC or CPT
Proof Test Coverage – The percentage failures that are detected during the servicing of equipment. In general it is assumed that when a proof test is performed any errors in the system are detected and corrected (100% proof test coverage).
Glossary Term: PSM
Process safety management. Part of the US requirement under the Occupational Safety and Health Administration (OSHA) guidelines for managing risk when dealing with large quantities of certain materials. The regulation (29 CFR 1910.119) was published in 1992 to help prevent or minimize the consequences of catastrophic releases of toxic, reactive,…
Glossary Term: Proportional control
A control mode in which there is a continual linear relationship between the deviation computer in the controller, the signal of the controller, and the position of the final control element.
Glossary Term: Proven in use
Basis for use of a component or system as part of a safety integrity level (SIL) rated safety instrumented system 〈SIS〉 that has not been designed in accordance with IEC 61508. It requires sufficient product operational hours, revision history, fault reporting systems, and field failure data to determine if the…
Glossary Term: Proof test
Testing of safety system components to detect any failures not detected by automatic on-line diagnostics i.e. dangerous failures, diagnostic failures, parametric failures followed by repair of those failures to an equivalent as- new state. Proof testing is a vital part of the safety lifecycle and is critical to ensuring that…
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