Glossary I

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

Icon: A graphic functional symbol display. A graphic representation of a function or functions to be performed by the computer.

ICP: Integrated Circuit Piezoelectric; term sometimes used to describe an accelerometer with built-in electronics.

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

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.

Initial Unbalance: Initial unbalance is that unbalance of any kind that exists in the rotor before balancing.

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

Input Impedance: The resistance of a panel meter as seen from the source. In the case of a voltmeter, this resistance has to be taken into account when the source impedance is high; in the case of an ammeter, when the source impedance is low.

Input Resistance (Impedance): The input resistance of a pH meter is the resistance between the glass electrode terminal and the reference electrode terminal. The potential of a pH-measuring electrode chain is always subject to a voltage division between the total electrode resistance and the input resistance.

Insulated Junction: See Ungrounded Junction

Insulation Resistance: The resistance measured between two insulated points on a transducer when a specific dc voltage is applied at room temperature.

Integral: A form of temperature control. See Automatic Reset, #2

Interchangeability Error: A measurement error that can occur if two or more probes are used to make the same measurement. It is caused by a slight variation in characteristics of different probes.

Interface: The means by which two systems or devices are connected and interact with each other.

Internal Reference Electrode (Element): The reference electrode placed internally in a glass electrode.

Interpreter: A system program that converts and executes each instruction of a high-level language program into machine code as it runs, before going onto the next instruction.

Interrupt: To stop a process in such a way that it can be resumed.

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.

Ionic Mobility: Defined similarly to the mobility of non-electrolytic particles, viz., as the speed that the ion obtains in a given solvent when influenced by unit power.

Ionic Strength: The weight concentration of ions in solution, computed by multiplying the concentration of each ion in solution (C) by the corresponding square of the charge on the ion (Z) summing this product for all ions in solution and dividing by 2:ionic strength – 1/2 _ Z2 C.

IPTS-48: International Practical Temperature Scale of 1948. Fixed points in thermometry as specified by the Ninth General Conference of Weights and Measures which was held in 1948.

IPTS-68: International Practical Temperature Scale of 1968. Fixed points in thermometry set by the 1968 General Conference of Weights and Measures.

Isolation: The reduction of the capacity of a system to respond to an external force by use of resilient isolating materials.

Isopotential Point: A potential which is not affected by temperature changes. It is the pH value at which dE/dt for a given electrode pair is zero. Normally, for a glass electrode and SCE reference, this potential is obtained approximately when immersed in pH 7 buffer.

Isothermal: A process or area that is a constant temperature.