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- I
- Symbol for electric current.
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- I/O
- Input/output--either analog or discrete.
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- IC
- Integrated Circuit (electronic components fabricated on a semiconductor
substrate which cannot be divided without losing its function).
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- IEC
- International Electromechanical Conference
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- Immediate Response
- Control transfers On/Off state immediately when target enters the detection
range, and reverses state immediately when target leaves detection range.
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- Impedance
- The total opposition of a circuit to the flow of
alternating current. It includes resistance and reactance,
and is measured in ohms.
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- 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.
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- Inductance
- The magnitude of a magnetic field created by a circuit carrying a current.
This can cause higher voltages in the circuit.
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- Inductive Analog Sensors
- Inductive analog sensors provide an absolute, analog
output signal (0 to 10 V / 4 to 20 mA).
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- Inductive Load
- Load such that alternating current lags behind alternating voltage; i.e.,
current does not change direction until after the voltage does.
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- 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.
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- 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.
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- 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.
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- Infrared Data Association (IrDA)
- Nonprofit organization whose goal is to develop globally adopted
specifications for infrared wireless communication.
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- Infrared-Emitting Diode (IRED)
- A diode capable of emitting radiant energy in the infrared region of the
spectrum.
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- 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.
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- 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.
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- Input High Selector
- Algorithm that specifies the process value (PV) or setpoint (SP) as higher
of two separate inputs.
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- Input Impedance
- Impedance (presented to the excitation source) measured across the
excitation terminals of a sensor.
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- Input Low Selector
- algorithm that specifies the process value (PV) or setpoint (SP) as lower of
two separate inputs.
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- 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.
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- Input Scaling
- The ability to scale input readings (readings in percent
of full scale) to the engineering units of the process
variable.
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- Input Type
- The signal type that is connected to an input, such as
thermocouple, RTD, linear or process.
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- Institute of Electrical and Electronics Engineers (IEEE)
- An American Society that establishes international standards in the
computing, electronic and telecommunications fields.
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- 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.
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- Insulation Resistance
- The resistance measured between specified insulated points on a sensor when
a specified DC potential is applied at room conditions.
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- Insulator
- A non-conducting support for an electric conductor. A material that does not
conduct electricity.
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- Integer
- A positive or negative whole number or 0.
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- Integral
- The function in a PI controller that adjusts the process
variable to the setpoint after system stabilization.
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- 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.
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- 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.
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- 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.
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- 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.
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- Integrator
- Device whose output is proportional to the integral of the input variable
with respect to lime.
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- 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.
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- Interference, Electromagnetic
- Any spurious effect produced in the circuits or elements of a device by
external electromagnetic fields.
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- 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.
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- 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).
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- Interpolation
- Using electronics and the laws of trigonometry, the
basic period is subdivided into smaller units. 10 times the
basic resolution is possible.
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- Interpreter
- Software enabling a computer to run programs statement by statement.
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- 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).
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- Interrupt
- An external signal causing the execution of a program to be suspended.
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- 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.
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- Intrinsically Safe
- Limits electrical/thermal energy to levels incapable of causing ignition.
External barriers are required.
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- Inverter
- A DC to AC converter.
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- 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.
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- IP
- European environmental ratings similar to USA NEMA ratings. International
classification system for the sealing effectiveness of enclosures of electrical
equipment against foreign bodies.
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- IPTS-48, -68
- International Practical Temperature Scales of 1948 and
1968. These have been superseded by ITS-90. See ITS-90.
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- ISA
- Industry Standard Architecture. An ISA expansion slot lets you plug data
acquisition boards into PCs.
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- 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).
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- 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.
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- Isolation
- The electrical separation between circuits from high voltage circuitry. Two
circuits are isolated when there is no direct electrical connection between
them.
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- 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.
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- 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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