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 at room temperature, with no load applied, and with the output terminals open-circuited.

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 (Isolation) Resistance: The DC resistance expressed in ohms measured between any electrical connector pin or lead wire and the transducer body or case. Normally measured at 50 VDC.

Integral Nonlinearity: This term describes the absolute accuracy of a converter. It is the maximum deviation, at any point in the transfer function, of the converter's output from its ideal value.

Integrated Services Digital Network (ISDN): A telephone service that brings a digital loop to the telephone subscriber's premises and integrates all forms of information (voice, computer data, facsimile, etc.) onto a single communications network.

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.

International Standards Organization (ISO): The standards organization that developed the Open Systems Interconnect Model and other international communications standards.

Internet: The global collection of interconnected regional and wide-area networks which use IP as the network layer protocol.

Internet Address: An assigned number which identifies a host in an Internet. It has two or three parts: network number, optional subnet number, and host number.

Internet Protocol (IP): The network layer protocol for the Internet. It is the datagram protocol defined by RFC 791.

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.

IOBASE-T Ethernet: A version of Ethernet that operates over twisted-pair wire at a speed of 10 Mb/s. IOBASE-T networks with more than two terminals must use an Ethernet hub and a star topology.

Ionic Mobility: Defined similarly to the mobility of nonelectrolytic 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.

ISA: Industry Standard Architecture (PC-AT Bus) or Instrument Society of America.

ISO: International Standards Organization.

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.