Absolute Pressure Transducer: A transducer that has an internal reference chamber sealed at or close to 0 psia (full vacuum) and normally provides increasing output voltage for increases in pressure.

Absolute Pressure: Gage pressure plus atmospheric pressure.

Absolute Zero: Temperature at which thermal energy is at a minimum. Defined as 0 Kelvin, calculated to be -273.15 °C or -459.67°F.

Absorption(of water vapor): retention (of water vapor) by penetration into the bulk of a material.technical glossary, technical terms, glossary, technical glossary

A/D Converter: (Also A/D or ADC) Short for analog-to-digital converter. Converts real-world analog signals into a digital format that can be processed by a computer.

AC Linearity: A dynamic measurement of how well an A/D performs. In an ideal A/D converter, a pure sine wave on the analog input appears at the digital output as a pure (sampled) sine wave. In the real world, however, spurious signals due to nonlinear distortion within the A/D appear in the digital output. These anomalies are usually combinations of harmonics of the fundamental and intermodulation products, produced when the fundamental and its harmonics beat with the sampled frequency.

Acceleration: The first derivative of velocity with respect to time. Units expressed in "g".

Accelerometer: A transducer which converts mechanical motion into an electrical signal that is proportional to the acceleration value of the motion.technical glossary, technical terms, glossary, technical glossary

Access Protocol: A defined set of procedures that function as an interface between a user and a network and enable the user to employ the services of that network.

Accuracy: The combined error of nonlinearity, repeatability, and hysteresis expressed as a percent of full scale output.

Acoustics: 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.

Acquisition Time: This term relates to sampling A/Ds which utilize a track/hold amplifier on the input to acquire and hold the analog input signal. Acquisition time is the time required by the T/H amplifier to settle to its final value after it is placed in the track module.

ACRS: Advisory Committee on Reactor Safeguards.technical glossary, technical terms, glossary, technical glossary

Active Filter: An active filter is one that uses active devices such as operational amplifiers to synthesize the filter response function. This technique has an advantage at high speeds because the need for inductors is eliminated.technical glossary, technical terms, glossary, technical glossary

Address: The label or number identifying the memory location where a unit of information is stored.

Adsorption (of water vapor): Retention (of water vapor) as a surface layer on a material ..technical glossary, technical terms, glossary, technical glossary

AEC: Atomic Energy Commission, 1947-1974. Broken up in 1974 into the Energy Research and Development Administration (ERDA) and the Nuclear Regulatory Commission (NRC). EDRA later became the Department of Energy.

AIX: Advanced Interactive Executive: IBM's version of UNIX.

Aliasing: In a sampled data system, the analog input must be sampled at a rate of at least twice the bandwidth of the signal in order to avoid loss of data (Nyquist Theorem). Adhering to the Nyquist Theorem prevents in-band "alias" signals, which are beat frequencies between the analog signal and the sampling clock that inherently occur.

Aliased Imaging: This is a technique, commonly applied to Direct Digital Synthesis, for using intentional aliasing as a source of high-frequency signals.

Alloy 11: A compensating alloy used in conjunction with pure copper as the negative leg to form extension wire for platinum-platinum rhodium thermocouples Types R and S.

Alloy 200/226: The combination of compensating alloys used with tungsten vs. tungsten 26% rhenium thermocouples as extension cable for applications under 200°C.

Alloy 203/225: The combination of compensating alloys used with tungsten 3% rhenium vs. tungsten 150 rhenium thermocouples as extension cable for applications under 200°C.

Alloy 405/426: The combination of compensating alloys used with tungsten 5% rhenium vs. tungsten 26% rhenium thermocouples as extension cable for applications under 870°C.

Alphanumeric: A character set that contains both letters and digits.

Alpha Decay: The emission of a nucleus of a helium atom from the nucleus of an element, generally of a heavy element, in the process of its radioactive decay.

Alpha Particle: The nuclei of a helium (with two neutrons and two protons each) that are discharged by radioactive decay of many heavy elements, such as uranium-238 and plutonium-239.

Alpha Radiation: Radiation consisting of helium nuclei (atomic wt. 4, atomic number 2) that are discharged by radioactive disintegration of some heavy elements, including uranium-238, radium-226, and plutonium-239.

Alumel: An aluminum nickel alloy used in the negative leg of a Type K thermocouple (Trade name of Hoskins Manufacturing Company).

AM: Amplitude Modulation

Ambient Compensation: The design of an instrument such that changes in ambient temperature do not affect the readings of the instrument.

Ambient Conditions: The conditions around the transducer (pressure, temperature, etc.)..technical glossary, technical terms, glossary, technical glossary

Ambient Pressure: Pressure of the air surrounding a transducer.

Ambient Temperature: The average or mean temperature of the surrounding air which comes in contact with the equipment and instruments under test.

Ammeter: An instrument used to measure current.

Ampere (amp): A unit used to define the rate of flow of electricity (current) in a circuit; units are one coulomb (6.25 x 108 electronics) per second.

Amplifier: A device which draws power from a source other than the input signal and which produces as an output an enlarged reproduction of the essential features of its input.technical glossary, technical terms, glossary, technical glossary

Analog Ground: In high-speed acquisition applications, system ground is generally physically separated into analog and digital grounds in an attempt to suppress digital switching noise and minimize its effect on noise-sensitive analog signal processing circuitry. Input signal conditioners, amplifiers, references, and A/D converters are usually connected to analog ground.

Analog Output: A voltage or current signal that is a continuous function of the measured parameter.

Analog-to-Digital Converter (A/D or ADC): A device or circuit that outputs a binary number corresponding to an analog signal level at the input.

Anemometer: An instrument for measuring and/or indicating the velocity of air flow.

Angstrom: Ten to the minus tenth meters (10-10) or one millimicron, a unit used to define the wave length of light. Designated by the symbol Å.

Angular Frequency: The motion of a body or a point moving circularly, referred to as the circular frequency O which is the frequency in cycles per second (cps) multiplied by the term (2) and expressed in radians per second (2pf).

Anion: A negatively charged ion (Cl-, NO3-, S2- etc.)

ANSI: American National Standards Institute.

Anti-reset Windup: This is a feature in a three-mode PID controller which prevents the integral (auto reset) circuit from functioning when the temperature is outside the proportional band.

Apparent Power: A value of power for AC circuits that is calculated as the product of RMS current times RMS voltage, without taking the power factor into account.

Application Program: A computer program that accomplishes specific tasks, such as word processing.

ARCHIE: A system for locating files that are publicly available by anonymous FTP.technical glossary, technical terms, glossary, technical glossary

ARP: Address Resolution Protocol. An Internet protocol which runs on ethernets and token rings and maps Internet addresses to MAC addresses.

ARPANET: Advanced Research Projects Agency Network. A pioneering long haul network funded by ARPA. It served as the basis for early networking research, as well as a central backbone furing the development of the internet.

ASCII: American Standard Code for Information Interchange. A seven or eight bit code used to represent alphanumeric characters. It is the standard code used for communications between data processing systems and associated equipment.

ASIC: Application specific integrated circuit.

ASME: American Society of Mechanical Engineers.

Assembler: A program that translates assembly language instructions into machine language instructions.

Assembly Language: A machine oriented language in which mnemonics are used to represent each machine language instruction. Each CPU has its own specific assembly language.

ASTM: American Society for Testing and Materials.

Asymmetry Potential: The potential developed across the glass membrane with identical solutions on both sides. Also a term used when comparing glass electrode potential in pH 7 buffer.

ATC: Automatic Temperature Compensation.

Atomic Number (symbolized Z): The number of protons in a nucleus. It determines the chemical properties of an element.

Atomic Weight: The nominal atomic weight of an isotope is given by the sum of the number of neutrons and protons in each nucleus. The exact atomic weight differs fractionally from that whole number because neutrons are slightly heavier than protons and the mass of the nucleus is also affected by the binding energy.

Auto-Zero: An automatic internal correction for offsets and/or drift at zero voltage input.

Automatic Reset: 1. A feature on a limit controller that automatically resets the controller when the controlled temperature returns to within the limit bandwidth set. 2. The integral function on a PID controller which adjusts the proportional bandwidth with respect to the set point to compensate for droop in the circuit, i.e., adjusts the controlled temperature to a set point after the system stabilizes.

AWG: American Wire Gage.

Axial Load: A load applied along or parallel to and concentric with the primary axis.