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Glossary Term: Ultrasonic flow meter
A device for measuring gauge pressure or differential pressure by means of a U shaped transparent tube partly filled with a liquid, commonly water; a small pressure above or below atmospheric is measured by connecting one leg of the U to the pressurized space and observing the height of liquid…
Glossary Term: U tube manometer
A device for measuring gauge pressure or differential pressure by means of a U shaped transparent tube partly filled with a liquid, commonly water; a small pressure above or below atmospheric is measured by connecting one leg of the U to the pressurized space and observing the height of liquid…
Glossary Term: Two-wire transmitter
Electronic transmitter which uses the power wires (typcally 24vdc) for signal transmission, usually by manipulating the current flow (typically 4-20mA) to represent the desired signal.
Glossary Term: Turbine flow meter
A volumetric flow measuring device using the rotation of a turbine type element to determine flow rate.
Glossary Term: Trim
The internal parts of a valve which are in flowing contact with the controlled fluid. Can be designed to any of the following requirements: Anti cavitation: reduces the tendency of the controlled liquid to cavitate. Anti noise: reduces the noise generated by fluid flowing through the valve. Balanced: minimizes the…
Glossary Term: Transient response
The response of a transducer to a step change of input. NOTE: Transient response, as such, is not shown in a specification except as a general heading, but is defined by such characteristics as time constant, response time, ringing period, etc.
Glossary Term: Torque tube flow meter
A device for measuring liquid flow through a pipe in which differential pressure due to the flow operates a bellows, whose motion is transmitted to a recorder arm by means of a flexible torque tube.
Glossary Term: Time constant
1. The value t in an exponential response term. For the output of a first order system forced by a step or an impulse, t is the time required to complete 63.2% of the total rise or decay. In higher order systems, there is a time constant for each of…
Glossary Term: Thermowell
A thermowell is a pressure tight receptacle adapted to receive a temperature sensing element and provided with external threads, flanges or other means for pressure tight attachment to a vessel.
Glossary Term: Thermojunction
Either of the two locations where the conductors of a thermocouple are in electrical contact; one, the measuring junction, is in thermal contact with the body whose temperature is being determined, and the other, the reference junction, is generally held at some known or controlled temperature.
Glossary Term: TI
Test Interval This acronym is typically used in risk analysis equations to represent the proof test interval described above. Temperature Indicator This acronym is used in piping and Instrumentation Diagrams (P&IDs) to designate a device with measures and displays the temperature.
Glossary Term: Thermocouple
Two dissimilar wires joined together that generate a voltage proportional to temperature when their junction is heated relative to a reference junction. See thermojunction.
Glossary Term: Thermistor
A temperature transducer constructed from semiconductor material and for which the temperature is converted into a resistance, usually with negative slope and highly nonlinear.
Glossary Term: Thermal type flow meter
An apparatus where heat is injected into a flowing fluid stream and flow rate is determined from the rate of heat dissipation; either the rise in temperature or some point downstream of the heater or the amount of thermal or electrical energy required to maintain the heater at a constant…
Glossary Term: Target flow meter
A device for measuring fluid flow rates through the drag force exerted on a sharp edged disk centered in a circular flow path due to differential pressure created by fluid flowing through the annulus. Usually, the disk is mounted on a bar whose axis coincides with the tube axis, and…
Glossary Term: Systematic failure
A failure that happens in a deterministic (non random) predictable fashion from a certain cause, which can only be eliminated by a modification of the design or of the manufacturing process, operational procedures, documentation, or other relevant factors. Since these are not mathematically predictable, the safety lifecycle includes a large…
Glossary Term: Suppressed range
A suppressed range is an instrument range which does not include zero. The degree of suppression is expressed by the ratio of the value at the lower end of the scale to the span.
Glossary Term: Supervisory control
A term used to imply that a controller output or computer program output is used as an input to other controllers. See SCADA.
Glossary Term: Stress corrosion cracking
Deep cracking in a metal part due to the combination of tensile stress and a corrosive environment, causing failure in less time than could be predicted by simply adding the separate effects of stress and the corrosive environment.
Glossary Term: Stochastic
Pertaining to direct solution by trial and error, usually without a step by step approach, and involving analysis and evaluation of progress made, as in a heuristic approach to trial and error methods. In a stochastic approach to a problem solution, intuitive conjecture or speculation is used to select a…
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