Glossary of Terms: I

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I
Symbol for electric current.
I/O
Input/output--either analog or discrete.
IC
Integrated Circuit (electronic components fabricated on a semiconductor substrate which cannot be divided without losing its function).
IEC
International Electromechanical Conference
Immediate Response
Control transfers On/Off state immediately when target enters the detection range, and reverses state immediately when target leaves detection range.
Impedance
The total opposition of a circuit to the flow of alternating current. It includes resistance and reactance, and is measured in ohms.
Incremental Encoder
Rotary encoder which outputs an electrical signal (HIGH/LOW) for every measuring step. Two signals phase-shifted by 90° and the zero signal are outputs. For zero point determination, it must first be referenced.
Inductance
The magnitude of a magnetic field created by a circuit carrying a current. This can cause higher voltages in the circuit.
Inductive Analog Sensors
Inductive analog sensors provide an absolute, analog output signal (0 to 10 V / 4 to 20 mA).
Inductive Load
Load such that alternating current lags behind alternating voltage; i.e., current does not change direction until after the voltage does.
Inductive Sensing
Sensing technique in which a metal target absorbs energy from an electromagnetic field generated by the sensor, causing the output state to switch.
Inductive Technology
Technology based on inductance, the property of an electric circuit by which an electromotive force is induced in it by a variation of current, either 1) in the circuit itself, or 2) in a neighboring circuit.
Infrared (IR)
A portion of the spectrum of light which is not visible (wavelengths which extend beyond 770nm). Invisible radiation (as opposed to visible light) that certain LEDs emit.
Infrared Data Association (IrDA)
Nonprofit organization whose goal is to develop globally adopted specifications for infrared wireless communication.
Infrared-Emitting Diode (IRED)
A diode capable of emitting radiant energy in the infrared region of the spectrum.
Input
1) The device or collective set of devices used for bringing data into another device; 2) The signal or stimulus taken in by an interface as indicators of the condition of process being controlled.
Input/Output (I/O)
Refers to the electronic hardware where the field devices are wired. Discrete I/O would have switches for inputs and, solenoid valves and pumps for outputs. Analog I/O would have process variable inputs, and controller outputs.
Input High Selector
Algorithm that specifies the process value (PV) or setpoint (SP) as higher of two separate inputs.
Input Impedance
Impedance (presented to the excitation source) measured across the excitation terminals of a sensor.
Input Low Selector
algorithm that specifies the process value (PV) or setpoint (SP) as lower of two separate inputs.
Input Signal Duration
A length of time the light beam is blocked (in dark operated mode), or uninterrupted (in light operated mode). Or, the length of time a target is within the operating range.
Input Scaling
The ability to scale input readings (readings in percent of full scale) to the engineering units of the process variable.
Input Type
The signal type that is connected to an input, such as thermocouple, RTD, linear or process.
Institute of Electrical and Electronics Engineers (IEEE)
An American Society that establishes international standards in the computing, electronic and telecommunications fields.
Instrument
Any item of electrical or electronic equipment which is designed to carry out a specific function or set of functions. For example an electronic balance, a gas analyzer or a chromatograph.
Insulation Resistance
The resistance measured between specified insulated points on a sensor when a specified DC potential is applied at room conditions.
Insulator
A non-conducting support for an electric conductor. A material that does not conduct electricity.
Integer
A positive or negative whole number or 0.
Integral
The function in a PI controller that adjusts the process variable to the setpoint after system stabilization.
Integral Action (I)
The integral part of the PID controller. With integral action, the controller output is proportional to the amount and duration of the error signal. If there is more integral action, the controller output will change more when error is present.
Integrated Circuit (IC)
An interconnected array of active and passive elements integrated within a single semiconductor substrate or other compatible material, and capable of performing one complete electronic function. An integrated circuit cannot be divided without losing its function.
Integrating Process
With these loops, making a small change in the controller output, will cause the process variable to ramp until it hits a limit. The larger the change, the faster the ramp. Also the smaller the integral time the faster it will move. It is a common misconception that integral time in the controller is not required to hold setpoint with an integrating process. Most control loops are self-regulating, so with a change in the controller output, the process variable will move and then settle. Integrating loops are also described as non-self-regulating.
Integration Time
The time over which an integrating A-D converter averages the input signal. If chosen appropriately will average over a complete mains cycle thereby helping to reduce mains frequency interference.
Integrator
Device whose output is proportional to the integral of the input variable with respect to lime.
Interface
Shared boundary. It might be a piece of hardware used between two pieces of equipment, or a software display communicating between the computer system and the people who use it.
Interference, Electromagnetic
Any spurious effect produced in the circuits or elements of a device by external electromagnetic fields.
Interface Circuit
Circuit that links one type of device with another. It's function is to produce the required current and voltage levels for the next stage of circuitry from the previous stage.
Internal Cascade
Control system composed of two loops where the SP of one loop (inner loop) is the output of the other loop (outer loop).
Interpolation
Using electronics and the laws of trigonometry, the basic period is subdivided into smaller units. 10 times the basic resolution is possible.
Interpreter
Software enabling a computer to run programs statement by statement.
Interrogate (Gate)
A function usually performed by gating light source-photoreceiver pair; asking (interrogating) whether a certain condition has been met (for example, proper fill level in boxes moving along a conveyor), and thereby enabling or disabling an inspect light source-photoreceiver pair (which will count only full boxes).
Interrupt
An external signal causing the execution of a program to be suspended.
Intrinsic Safety
Method for safe operation of electric process control instrumentation where hazardous atmospheres exist. System that requires very little energy to operate. Should there be a wire breakage or fault, it must not be capable of igniting a flammable mixture.
Intrinsically Safe
Limits electrical/thermal energy to levels incapable of causing ignition. External barriers are required.
Inverter
A DC to AC converter.
Ion Implantation
A process where impurity ions are accelerated to a specific energy level and impinged upon the silicon wafer. The energy level determines the depth to which the impurity ions penetrate the silicon. Impingement time determines the impurity concentration. Thus, it is possible to independently control these parameters, and buried piezoresistors are easily produces. Ion implantation is increasingly used throughout the semiconductor industry to provide a variety of products with improved performance over those produced by diffusion.
IP
European environmental ratings similar to USA NEMA ratings. International classification system for the sealing effectiveness of enclosures of electrical equipment against foreign bodies.
IPTS-48, -68
International Practical Temperature Scales of 1948 and 1968. These have been superseded by ITS-90. See ITS-90.
ISA
Industry Standard Architecture. An ISA expansion slot lets you plug data acquisition boards into PCs.
ISO
International Organization for Standardization, which is made up of national members. A member is the "most representative of standardization in its country". For example BSI (British Standards Institute), DIN (Deutsches Institut für Normung) and ANSI (American National Standards Institute).
Isolated Circuit
circuit in which the current, with the equipment at reference-test conditions, to any other circuit or conductive part does not exceed limit for leakage current.
Isolation
The electrical separation between circuits from high voltage circuitry. Two circuits are isolated when there is no direct electrical connection between them.
Isolation to Earth or System
A high transient voltage at one input may damage not only the input circuit, but the rest of the data acquisition hardware, and, by propagating through the signal conditioning and A-D circuits, eventually damage the computer system as well. You can prevent this type of damage by isolating the input from the earth of the data acquisition and computer hardware.
ITS-90
International Temperature Scale of 1990 is the standard scale made of fixed points that closely approximate thermodynamic temperatures. All temperatures between the fixed points are derived by interpolation. Adopted in late 1993, this scale replaces both IPTS-48 and IPTS-68.
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