Exergen Glossary Of Terms

A

ABS (Acrylonitrile Butadiene Styrene): A family of resins created by polymerizing two liquids and a gas. The result is a thermoplastic which is strong, long-wearing and resistant to stains and chemicals.

Absolute Zero: Temperature at which thermal energy is at a minimum. Defined as 0 Kelvin or 0 Rankine (-273.15°C or - 459.67°F)

Absorptivity: A measure of an object's ability to absorb incident energy.

Accuracy: Closeness of a reading or indication of a measurement device to the actual value of the quantity measured.

Automatic Emissivity Compensation System: (AECS) The patented system utilized in the handheld D and DX Series of instruments. It produces NIST traceable accuracy on real surfaces of unknown emissivity (0.8 - 1.0), while completely free of contact errors and heat sinking errors of contact devices.

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

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.

A.N.S.I.
- American National Standards Institute.


B

Background Noise:
Radiation originating from the detector environment induces background radiation noise. The extent of background radiation noise is dependent on the temperatures, emissivities, and geometry of such elements as the detector walls, window, and media as seen by the detector element.

Blackbody: A theoretical object that radiates the maximum amount of energy at a given temperature, and absorbs all the energy incident upon it. A blackbody is not necessarily black. (The name blackbody was chosen because the color black is defined as the total absorption of light energy).

Boiling point: The temperature at which a substance in the liquid phase transforms to the gaseous phase. Commonly refers to the boiling point of water, 100°C (212°F).


C

Calibration: The process of adjusting an instrument or compiling a deviation chart so that its reading can be correlated to the actual value being measured.

Celsius (Centigrade): A temperature scale defined by 0°C at the ice point and 100°C at the boiling point of water.

Cold Junction or Reference Junction:
The junction generally at the measuring device that is held at a relatively constant temperature.

Cold Junction Compensation:
Measures the ambient temperature at the connection of the thermocouple wire to the measuring device. This allows for accurate computation of the temperature at the hot junction by the measuring device.

Compensation:
An addition of specific materials or devices to counteract a known error.

Cryogenics:
The measurement of very low temperatures. i.e. below -200°C.

Current: The rate of flow of electricity. The unit is the ampere (a) defined as 1 ampere = 1 coulomb per second


D

Data Acquisition System: Electronic devices which acquire data.

Datalogger: Measures an electrical signal, converts it to a number and stores that value.

Degree: An incremental value in temperature scale.

Digital Output: An output signal which represents the size of an input in the form of a series of discrete quantities.

Drift: A change in an instrument's reading or setpoint value over extended periods due to factors such as time, line voltage, or ambient temperature effects.


E

Electrostatic: Type of force that exists between two electrically charged objects. Objects with a similar charge repel each other , and objects with dissimilar charges attract each other . No current flows in an electrostatic environment .

Emissivity:
The ratio of energy emitted by a surface to the energy emitted by a blackbody at the same temperature. Non metal surfaces are have high emissivity (~0.9) and shiny metal surfaces have low emissivity (~0.2).

Error: The difference between the value indicated by the transducer and the true value of the measurand being sensed. Usually expressed in percent of full scale output.

Extension Wire: Wires which connect the thermocouple itself to a reference junction, i.e. controller, receiver, recorder, etc. Extension wire must be of the same type as the thermocouple. Special plugs and jacks made of the same alloys as the thermocouple should be used if a quick disconnect is required for the application.

Extrusion: The act or process of shaping by forcing through a die.


F

Fahrenheit:
A temperature scale defined by 32° at the ice point and 212° at the boiling point of water at sea level.

Field of View: A volume in space defined by an angular cone extending from the focal plane of an instrument. It' The ratio of distance from target to sensor to spot size (i.e. at 3" away measuring a 1" spot, the field of view is 3:1)

Freezing Point: The temperature at which the substance goes from the liquid phase to the solid phase.


G

Gray-body: Materials that have an emissivity less than 1.


H

Heat Balance Series: The patented technique which calculates the internal temperature of a product by solving the equation that describes the heat balance between internal, surface, and ambient temperatures, and produces an unpowered thermocouple signal that represents the internal temperature.

Hot Junction: The measuring junction

I

Impedance: The total opposition to electrical flow (resistive plus reactive).

Induction: The production of an electric current in a conductor by the variation of a magnetic field in its vicinity.

Infrared: An area in the electromagnetic spectrum extending beyond red light from 760 nanometers to 1000 microns (106 nm). It is the form of radiation used for making non-contact temperature measurements.

Input Impedance: The resistance measured across the excitation terminals of a transducer.

Intrinsically Safe: An instrument which will not produce any spark or thermal effects under normal or abnormal conditions that will ignite a specified gas mixture.

IRt/c: Infrared Thermocouple, a patented, self powered infrared temperature sensor which emulates a thermocouple (J, K, etc.) at temperatures close to its calibration point.

J

Junction: The point in a thermocouple where the two dissimilar metals are joined.

K

Kelvin: Symbol K. The unit of absolute or thermodynamic temperature scale based upon the Celsius scale with 100 units between the ice point and boiling point of water. 0°C = 273.15K (there is no degree (°) symbol used with the Kelvin scale).

L

Leakage Current: A flow of electricity that originates from two sources within a readout device: leakage current actually generated by the input amplifier, and leakage current intentionally injected to the thermocouple circuit to detect an open circuit due to wire breaks.

Linearity: The closeness of a calibration curve to a specified straight line. Linearity is expressed as the maximum deviation of any calibration point on a specified straight line during any one calibration cycle.

M

Measuring Junction: The junction in a thermocouple which actually measures the temperature of the object. Often referred to as the Hot Junction.

Melting Point: The temperature at which a substance transforms from a solid phase to a liquid phase.

Microvolt: One millionth of a volt, 10-6 volts.

Milliamp: One thousandth of an amp, 10-3 amps, symbol mA.

Millivolt: Unit of electromotive force. It is the difference in potential required to make a current of 1 millampere flow through a resistance of 1 ohm; one thousandth of a volt, symbol mV.

N

NEMA-4: A standard from the National Electrical Manufacturers Association, which defines enclosures intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, and hose-directed water.

N.I.S.T. - National Institute of Standards and Technology. Formerly known as National Bureau of Standards (NBS).

 

O

Offset: The difference in temperature between the set point and the actual process temperature. Also, referred to as droop.

Ohmeter:
An instrument used to measure electrical resistance.

Open Circuit:
The lack of electrical contact in any part of the measuring circuit. An open circuit is usually characterized by rapid large jumps in displayed potential, followed by an off-scale reading.

Output Impedance:
The resistance as measured on the output terminals of a pressure transducer.


P

Planck Function: All material systems can absorb or give off electromagnetic radiation only in "chunks" of energy, quanta E, and that these are proportional to the frequency of that radiation E = h. (The constant of proportionality h is, as noted above, called Planck's constant.)

Polynomial: An algebraic expression consisting of one or more summed terms, each term consisting of a constant multiplier and one or more variables raised to integral powers. For example, x2 - 5x + 6 and 2p3q + y are polynomials.

Potentiometer: 1. A variable resistor often used to control a circuit. 2. A balancing bridge used to measure voltage.

Programmable Logic Controllers (PLCs): Also referred to as programmable controllers, are in the computer family. They are used in commercial and industrial applications. A PLC monitors inputs, makes decisions based on its program, and controls outputs to automate a process or machine.

Proportioning Control with Integral and Derivative Functions: Three mode PID controller. A time proportioning controller with integral and derivative functions. The integral function automatically adjusts the system temperature to the set point temperature to eliminate droop due to the time proportioning function. The derivative function senses the rate of rise or fall of the system temperature and automatically adjusts the cycle time of the controller to minimize overshoot or undershoot.

Psychometrics: The science of measurement and control of moisture in air, is based entirely on thermodynamics of air and water: the properties and temperature.

R

Radiation: a. Emission and propagation and emission of energy in the form of rays or waves. b. Energy radiated or transmitted as rays, waves, in the form of particles.

Range: Those values over which a transducer is intended to measure, specified by its upper and lower limits.

Reference Junction: The cold junction in a thermocouple circuit which is held at a stable known temperature. The standard reference temperature is 0°C (32°F). However, other temperatures can be used.

Reflectance: The fraction or percent of a particular frequency or wavelength of electromagnetic radiation that is reflected from the surface of a substance without being absorbed or transmitted.

Relative Humidity: (RH) is one of the common parameters used to describe the psychrometric state of air in an environment, in an oven,

Repeatability: The ability of a transducer to reproduce output readings when the same measured value is applied to it consecutively, under the same conditions, and in the same direction. Repeatability is expressed as the maximum difference between output readings.

Resolution: The act or process of separating or reducing something into its constituent parts.

Response Time (time constant): The time required by a sensor to reach 63.2% of a step change in temperature under a specified set of conditions. Five time constants are required for the sensor to stabilize at 600 of the step change value.

S

Seebeck Coefficient: The derivative (rate of change) of thermal EMF with respect to temperature normally expressed as millivolts per degree.

Seebeck Effect:
When a circuit is formed by a junction of two dissimilar metals and the junctions are held at different temperatures, a current will flow in the circuit caused by the difference in temperature between the two junctions.

Seebeck EMF: The open circuit voltage caused by the difference in temperature between the hot and cold junctions of a circuit made from two dissimilar metals

Signal Conditioner: A circuit module which offsets, attenuates, amplifies, linearizes and/or filters the signal for input to the A/D converter. The typical output signal conditioner is +2 V dc.

Signal Conditioning:
To process the form or mode of a signal so as to make it intelligible to, or compatible with, a given device, including such manipulation as pulse shaping, pulse clipping, compensating, digitizing, and linearizing.

Signal: An electrical transmittance (either input or output) that conveys information.

Span: The difference between the upper and lower limits of a range expressed in the same units as the range.

Spectral Filter: A filter which allows only a specific band width of the electromagnetic spectrum to pass, i.e., 4 to 8 micron infrared radiation.

Spectral Response: The photocurrent produced by a given level of incident light varies with the wavelength. This relation between the photoelectric sensitivity and wavelength is referred to as the spectral response characteristic and is expressed in terms of photosensitivity, quantum efficiency, etc.

Spectrum: The resolving of overall vibration into amplitude components as a function of frequency.

Spot Size: The diameter of the circle formed by the cross section of the field of view of an optical instrument at a given distance

Stability: The quality of an instrument or sensor to maintain a consistent output when a constant input is applied.

T

TEMPCO: Abbreviation for "temperature coefficient": the error introduced by a change in temperature. Normally expressed in %/°C or ppm/°C.

Temperature: Measure of the energy in a substance. The more heat energy in the substance, the higher the temperature

Temperature Error: The maximum change in output, at any measurand value within the specified range, when the transducer temperature is changed from room temperature to specified temperature extremes.

Temperature Range, Compensated: The range of ambient temperatures within which all tolerances specified for Thermal Zero Shift and Thermal Sensitivity Shift are applicable (temperature error).

Temperature Range, Operable:
The range of ambient temperatures, given by their extremes, within which the transducer may be operated. Exceeding compensated range may require recalibration

Thermistor: Temperature measurement devices that are semiconductors with large coefficients of resistance typically used in the range of -100 to 300°C.

Thermocouple: A temperature sensor based on the principle that a voltage is produced when two dissimilar metals. The junction produces a voltage in proportion to the difference in temperature between the measuring junction and the reference junction.

Thermoforming: Any process of forming thermoplastic sheet, which consists of heating the sheet and forcing it onto a mold surface.

Thermopile: a set of thermocouple junctions connected in series in order to boost the voltage to a meaningful amount (usually measured in millivolts)

Thermowell: A threaded or flanged closed end tube which is mounted directly to the process or vessel, designed to protect the thermocouple from the process surroundings.

Transmittance: the fraction or percent of a particular frequency or wavelength of electromagnetic radiation that passes through a substance without being absorbed or reflected.

Transmitter: A device used to transmit millivolts from a thermocouple or ohms from an RTD via a current loop.

V

Vacuum: A space in which the pressure is significantly lower than atmospheric pressure.

Vacuum forming: A method of forming in which a plastic sheet is clamped in a stationary frame, heated and forced down by a vacuum onto a mold.

Volt: The work per unit change or potential difference between two points in a circuit.

Voltage: An electrical potential.

Back to Education Center