Glossary of terms used on this siteThere are 823 entries in this glossary.
|A/D (Analog to Digital) Converter||
A circuit or device that produces a digital output representing the magnitude of an analog input signal.
Gage pressure plus atmospheric pressure.
|Absolute Pressure Transducer||
A transducer which measures pressure in relation to zero pressure (a vacuum on one side of the diaphragm).
Temperature at which thermal energy is at a minimum. Defined as 0 Kelvin, calculated to be -273.15°C or -459.67°F.
Alternating current; an electric current that reverses its direction at regularly recurring intervals.
A change in the velocity of a body or particle with respect to time. The parameter that an accelerometer measures (dv/dt). Units expressed in "g".
A device which converts the effects of mechanical motion into an electrical signal that is proportional to the acceleration value of the motion. A sensor. A transducer.
(Process Control Terminology) A device that is mounted on the actuator to complement the actuator's function and make it a complete operating unit. Examples include positioners, supply pressure regulators, solenoids, and limit switches.
The quality of closeness to a specified value under stated conditions. Usually expressed as uncertainty - the maximum deviation to be expected between a reading or output and the actual value being measured.
The degree of sound. The nature, cause, and phenomena of the vibrations of elastic bodies; which vibrations create compressional waves or wave fronts which are transmitted through various media, such as air, water, wood, steel, etc.
Microsoft's toolkit for Web developers, using OLE and incorporating Sun's Java language. ActiveX helps in building software to integrate with Microsoft's Internet Explorer, or any ActiveX container such as programs written with Microsoft's Visual Studio.
A thermodynamic term for the apparent or active concentration of a free ion in solution. It is related to concentration by the activity coefficient.
|Activity Coefficient (fi)||
A ratio of the activity of species i(ai) to its molality (C). It is a correction factor which makes the thermodynamic calculations correct. This factor is dependent on ionic strength, temperature, and other parameters.
Individual ionic activity coefficients, f+ for cation and f- for an anion, cannot be derived thermodynamically. They can be calculated only by using the Debye-Huckel law for low concentration solutions in which the interionic forces depend primarily on charge, radius, and distribution of the ions and on the dielectric constant of the medium rather than on the chemical properties of the ions.
Mean ionic activity coefficient (f±) or the activity of a salt, on the other hand, can be measured by a variety of techniques such as freezing point depression and vapor pressure as well as paired sensing electrodes. It is the geometric mean of the individual ionic activity coefficients: f± = (f+n+f-n-)1/n
(Process Control Terminology) A pneumatic, hydraulic, or electrically powered device that supplies force and motion to open or close a valve.
(Process Control Terminology) An actuator, including all the pertinent accessories that make it a complete operating unit.