Glossary E

Following is a definition of terms frequently used in the instrumentation, industrial automation and test & measurement communities.

Echo: To reflect received data to the sender. For example, keys depressed on a keyboard are usually echoed as characters displayed on the screen.

Electrical Interference: Electrical noise induced upon the signal wires that obscures the wanted information signal.

Electrode Potential (E): The difference in potential established between an electrode and a solution when the electrode is immersed in the solution.

Electrolyte: Any substance which, when in solution will conduct an electric current. Acids, bases, and salts are common electrolytes.

Electromotive Force (emf): The potential difference between the two electrodes in a cell. The cell emf is the cell voltage measured when no current is flowing through the cell. It can be measured by means of a pH meter with high input impedance.

Electronic Industries Association (EIA): A standards organization specializing in the electrical and functional characteristics of interface equipment.

EMF: Electromotive Force. A rise in (electrical) potential energy. The principal unit is the volt.

EMI: Electromagnetic interference.

Emissivity: The ratio of energy emitted by an object to the energy emitted by a blackbody at the same temperature. The emissivity of an object depends upon its material and surface texture; a polished metal surface can have an emissivity around 0.2 and a piece of wood can have an emissivity around 0.95.

End Point (Potentiometric): The apparent equivalence point of a titration at which a relatively large potential change is observed.

End Points: The end points of a full scale calibration curve.

Endothermic: Absorbs heat. A process is said to be endothermic when it absorbs heat.

Enthalpy: The sum of the internal energy of a body and the product of its volume multiplied by the pressure.

Environmental Conditions: All conditions in which a transducer may be exposed during shipping, storage, handling, and operation.

Eprom: Erasable Programmable Read-Only Memory. The PROM can be erased by ultraviolet light or electricity.

Equilibrium Constant: The product of the concentrations (or activities) of the substances produced at equilibrium in a chemical reaction divided by the product of concentrations of the reacting substances, each concentration raised to that power which is the coefficient of the substance in the chemical equation.

Equitransference: Equal diffusion rates of the positively and negatively charged ions of an electrolyte across a liquid junction without charge separation.

Equivalent Conductance (l): Equivalent conductance of an electrolyte is defined as the conductance of a volume of solution containing one equivalent weight of dissolved substances when placed between two parallel electrodes 1 cm apart, and large enough to contain between them all of the solution. l is never determined directly, but is calculated from the specific conductance (Ls). If C is the concentration of a solution in gram equivalents per liter, then the concentration of a solution in gram equivalents per liter, then the concentration per cubic centimeter is C/1000, and the volume containing one equivalent of the solute, is, therefore, 1000/C.

Error Band: The allowable deviations to output from a specific reference norm. Usually expressed as a percentage of full scale.

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.

Eutectic Temperature: The lowest possible melting point of a mixture of alloys.

Excitation: The external application of electrical voltage current applied to a transducer for normal operation.

Exothermic: Gives off heat. A process is said to be exothermic when it releases heat.

Expansion Factor: Correction factor for the change in density between two pressure measurement areas in a constricted flow.

Explosion-proof Enclosure: An enclosure that can withstand an explosion of gases within it and prevent the explosion of gases surrounding it due to sparks, flashes or the explosion of the container itself, and maintain an external temperature which will not ignite the surrounding gases.

Exposed Junction: A form of construction of a thermocouple probe where the hot or measuring junction protrudes beyond the sheath material so as to be fully exposed to the medium being measured. This form of construction usually gives the fastest response time.