Process Control Definitions and Terminology


I

Immediate Response
-control transfers On/Off state immediately when target enters the detection range, and reverses state immediately when target leaves detection range.

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)
-the invisible radiation (as opposed to visible light) that certain LEDs emit. Standard MICRO SWITCH modulated LED controls have infrared emitting LEDs.

Input
-1) The device or collective set of devices used for bringing data into another device; 2) The signal or stimulus put into a circuit to make the output do something.

Input Impedance
-the impedance (presented to the excitation source) measured across the excitation terminals of a sensor.

Input Signal Duration-a length of time the light beam is blocked (in dark operated mode), or uniterrupted (in light operated mode). Or, the length of time a target is within the operating range.

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.

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.

Interface
-a common boundary between electronic systems, or parts of a single system.

Interface Circuit
-a 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.

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).

Intrinsically Safe
-limits electrical/thermal energy to levels incapable of causing ignition. External barriers are required.

IP
-European environmental ratings similar to USA NEMA ratings.

Ion Implantation
-a process whereby 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.

IR
-Infrared: A portion of the spectrum of light which is not visible (wavelengths which extend beyond 770nm).

IRED
-Infrared-Emitting Diode: a diode capable of emitting radiant energy in the infrared region of the spectrum.
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J

K

L

Laser Trimming (Automated)
-a method for adjusting the value of thick film resistors using a computer-controlled laser system.

Latching Logic
-signal modification that causes the output to be energized and remain energized (maintain output). Latched output may be immediate or delayed. Usually, the latch is released by closing a circuit between the reset (RS/D) terminal and ground.

Leakage Current
-small current flowing through or leaking from the output device in the Off state due to semiconductor characteristics.

Leakage Rate
-the maximum rate at which a fluid is permitted or determined to leak through a seal. The type of fluid, the deferential pressure across the seal, the direction of leakage, and the location of the seal must be specified.

Least Squares Line
-the straight line for which the sum of the squares of the residuals (deviations) is minimized. This method is used to calculate B.F.S.L. linearity.

LED (Light Emitting Diode)
-a solid state light source that emits variable light, or (in MICRO SWITCH modulated LED controls) invisible, infrared radiation.

Light Operated (L.O.)
-control operating mode in which the output is energized when the light beam is not blocked (retro/thru scan), or object is present (diffuse) the photosensor is illuminated.

Linearity (Linearity Error)
-the deviation of the sensor output curve from a specified straight line. Linearity error is usually expressed as a percent of full scale output.

Linearity (End Point)
-see Terminal Base Linearity

Linear (Output)
-output that is a continuous amplified version of its input. That is, the output is a predetermined variation of its input.

Linearity (Terminal Base)
-see Terminal Base Linearity.

Load Current
-units = Amps/milliamps (DC) or Amps RMS/milliamps RMS (AC). The maximum amount of current that a proximity sensor will switch through its load. Load current for a particular device can be calculated by dividing the load voltage by the load resistance. Attempting to switch a higher load current than the sensor is rated for will result in sensor failure.

Load Impedance
-the impedance presented to the output terminals of a sensor by the associated external circuitry.

Logic
-the modification of an input signal that produces delayed, pulsed, latched. or other output response. Logic circuitry is sometimes an integral part of the control, but more often, a separate plug-in card or module.

Low Contamination
-warehouse locations, light industry applications, material handling operations.

Low Energy Circuit
-a qualitative term having no exact definition. It usually refers to a circuit having such low voltage and current that there are no significant thermal effects at the contact interface.
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M

Magnetic Blow-Out Switch
-contains a small permanent magnet which provides a means of switching high DC loads. The magnet deflects arc to quench it.

Maintained Contact Switch
-designed for applications requiring sustained contact after plunger has been released, but with provision for resetting.

Manufacturer's Tolerance
-the maximum variation from standard allowed by the manufacturer between products with the same catalog listing.

Make
-to close or establish an electrical circuit.

Maximum Excitation
-the maximum value of supply voltage or current that can be applied to the sensor at room conditions without causing damage or performance degradation beyond specified tolerances.

Maximum Load Current
-the maximum amount of current that can flow through a sensor and not cause sensor failure.

Measurand
-a physical quantity, property or condition which is measured (e.g., pressure, acceleration).

Mechanical Life
-life of a switch with no (or a negligible) electrical load, and a specified combination of actuation, environment and criterion of failure. Mechanical life usually is limited by the life of the switch's flexing parts and bearing surfaces.

Media compatibility
-ability to operate with a specified media carrying pressure (e.g., salt water).

Metalization
-the metal pattern deposited on the sensor chip (usually outside the diaphragm area) to permit electrical connections to be made to the chip. Aluminum is usually used, but has potential contamination problems (known as the "purple plague"), if not protected. MICRO SWITCH uses gold, which is impervious to almost everything.

Migration, Contact Material
-a net transfer of material from one contact to the mating contact as a result of switching an electrical load. It usually takes the form of a needle, cone or mound or one contact face and a corresponding pit in the surface of the mating contact.

Minimum Life
-this is an exact term only when applied to a specific group of tested switches. It then means the lowest life figure obtained from the test of that group of switches.

Moderate Contamination
-milling operations, areas of high humidity, stream.

Modulated Light Source (MLS) Control
-a photoelectric control that operates on modulated (pulsed) infrared radiation, and responds only to that frequency rather than steady light intensity. Modulated LED controls offer a high rejection of troublesome ambient light.

Momentary Short Circuit Protection
-output circuit protection designed to protect the output device from damage due to a temporary (1-3 sec.) short circuit or until an external fuse can interrupt current.

Momentary Short Circuit
-a switch with contacts that return from operated condition to normal condition when actuating force is removed. Unless otherwise stated, all switches in this catalog are momentary.

Momentary Switch
-a switch with contacts that return from operated condition to normal condition when actuating force is removed. Unless otherwise stated, all switches in this catalog are momentary.
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N

NEMA Ratings
-National Electrical Manufacturers Association ratings of an enclosure's ability to provide a degree of protection against contact with equipment and against specified environmental conditions.

Noise, Electrical
-noise results from the presence of undesirable electrical voltages or current. It causes devices to operate erratically (if the noise is on the supply line to a device), or produces false information on erratic operation if present on wires carrying signals from the output of a device to the load. Noise can be present in the supply or picked up on lines in many ways. Pick-up from noisy adjacent wires or metal parts is possible. Good wiring practice and/or additional parts can be used to diminish the effects of noise.

Nominal Sensing Distance
-an approximate dimension value measured from the face of the sensor to the nearest point of the target. It does not take into consideration manufacturer's tolerance or operational variables. Also known as the operating point.

Non-contact
-a slang expression referring to a defective condition in which a supposedly closed switch lacks electrical continuity.

Nonincendive
-inability under normal operation to ignite a hazardous mixture.

Non-modulated Controls
-controls designed for indoor applications subject to neither bright ambient light nor extreme vibration. Usually incandescent lamp controls, scanners and light source-photoreceiver pairs.

Normal Contact Position
-the normal contact position of a switch exits when no force is applied to the plunger.

Normal High
-the state of a control in which the output is high (logic1) in voltage in the rest (Off) condition.

Normally Low
-the state of a control in which the output is low (logic 0) in voltage in the rest (Off) condition.

Normalization
-process of creating sensor interchangeability.

NPN
-a transistor consisting of two N-type regions separated by a P-type region.

Null
-the condition when the pressure on each side of the sensing diaphragm is equal.

Null Offset
-the electrical output present, when the pressure sensor is at null.

Null Temperature Shift

-the change in null output value due to a change in temperature.
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O

Off Delay Logic
-adjustable delay (after input signal stops) before output is de-energized.

Off State Current
-the supply or bias current flowing into a solid state device when it is in the unactuated state (see Leakage Current).

Ohm
-the unit of electrical resistance. Resistance through which a current of one ampere will flow when a voltage of one volt is applied.

On Delay Logic
-adjustable delay (after onset of input signal) before output is energized.

One-shot Logic
-see pulsed logic .

Opacity
-the characteristic of an object that prevents light from passing through. The opposite of translucent. Opaque objects are easy to detect since they block light almost entirely.

Operated Contact Position
-the position to which the contacts move when the plunger is traveled to the operating point or into the overtravel range.

Operating Characteristics of a Switch
-the commonly specified force, torque and linear or angular travel properties of a switch. Examples: operating or release force, operating point, differential, overtravel.

Operating Force
-the force which must be applied to the plunger to cause the moving contact to snap from the normal contact position to the operated contact position.

Operating Mode
-refers to the condition of the photosensor (dark or light illuminated) that energizes output. A mode selector switch determines the operating mode.

Operating Point
-that position of the plunger at which the contacts snap from the normal contact position to the operated contact position.

Operating Temperature
-actual range over which sensors can be operated. Usage outside the temperature limits will result in loss of stability, change in operate point and possible permanent damage to the sensor. Nominal sensing distance is determined at 25 - C.

Optical Power
-power or intensity of the projected light available from a particular emitter; beam intensity.

OR Logic
-an output is produced when any one or more inputs are present.

Output
-the useful energy delivered by a circuit or device. Can mean energy produced at the output terminals of an amplifier-a source of energy.

Output Impedance
-the impedance across the output terminals of a sensor presented by the sensor to the associated external circuitry.

Output Noise
-the rms, peak-to-peak (as specified) AC component of a sensors DC output in the absence of a change in input pressure.

Overpressure
-the maximum specified pressure which may be applied to the sensing element of a sensor without causing a permanent change in the output characteristics.

Overtravel
-as an operating characteristic of a switch, overtravel is the distance through which the plunger moves when traveled from the operating point to the full overtravel point. As a characteristic of the actuation applied to the switch, overtravel is the distance the plunger is driven past the operating point.
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P

Parallel Circuit
-a circuit in which current has two or more paths to follow. Two electrical elements are in parallel if both terminals of both elements are electrically connected.

Photocell
-a resistive, bulk effect type of photosensor, the type used when it is desirable to wire several photoreceivers in series or in parallel. The resistance decreases with increasing light intensity.

Photoreceiver
-a unit consisting of photosensor, focusing lens, and protective enclosure.

Photosensor
-a light sensitive portion of a photoelectric control that converts a light signal into an electrical signal. MICRO SWITCH uses photocells and phototransistors.

Phototransistor
-a type of photosensor. Typically used where speed of response is important or ambient temperature variations are great.

Piezoresistance
-a change in resistance in a semiconductor, caused by an applied stress to the diaphragm.

Polarized Photoelectric Controls
-controls that emit a visible LED beam and use a special lens which filters the beam of light so that it is projected in one plane only. The control responds only to the de-polarized reflected light from corner-cube type reflectors (FE-RR1) or special polarized reflective tape.

PN
-a diode consisting of one N-type region and one P-type region.

Pole
-the number of completely separate circuits that can pass through a switch at one time. A single pole switch can control only one circuit at a time. A double pole switch can control two independent circuits (such as a 120 volt AC heater and a 6 volt DC lamp) at the same time. The number of poles is completely independent of the number of throws and number of breaks.

Polymers Between Contacts
-compounds having long-chain molecular structure, formed from simple organic contaminants on contacts, under the influence of contact wipe and the catalytic effect of the contact material.

Power Dissipation
-units = Watts/milliwatts (DC) or Volt-Amps (AC). The amount of power that is consumed and converted to heat in normal operation. Supply Voltage (max) x Supply Current (max) = Power Dissipation Volts x Amps = Watts (DC) or Volt/Amps (AC)

Precision Snap-Acting Switch
-an electromechanical switch having predetermined and accurately controlled characteristics and having a spring loaded quick make and break contact action.

Pressure
-force applied to, or distributed over a surface expressed in terms of force to area ratio.

Pressure, Absolute
-pressure measured relative to absolute zero pressure (perfect vacuum). The output of the absolute sensor will change as a result of barometric pressure change. Thus it can be used as a barometer.

Pressure, Differential
-pressure between two points of measurement.

Pressure, Gage
-pressure measured relative to ambient pressure. The output of a gage pressure sensor, contrasted to an absolute pressure sensor, does not change with a change of barometric pressure.

Pressure Range
-the pressure limits over which the pressure sensor is calibrated or specified.

Pressure, Reference
-the pressure relative to which a differential sensor measures pressure. Ambient pressure is a specific case of reference pressure.

Pressure Sensor
-a device that converts an input pressure into an electrical output.

Pressure, Static
-the average pressure on the inputs of a differential pressure sensor (sometimes referred to as common mode or working pressure).

Pretravel
-the distance through which the plunger moves when traveled from the free position to the operating point.

Proof Pressure
-see Overpressure.

Proximity Sensor
-a sensor with the ability to detect the presence of a metal target, within a specified range, and without making physical contact.

Pull-Down Resistor
-a resistor connected across the output of a device or circuit to hold the output equal to or less than the zero input level. Also used to lower output impedance of digital or analog devices. Usually connected to a negative voltage or ground.

Pull-Up Resistor
-a resistor connected across the output of a device or circuit to hold the output voltage equal to or greater than the input transition level of a digital device. Usually connected to the positive voltage or plus supply.

Pulse
-a momentary sharp change in current, voltage, or other quantity that is normally constant. A pulse is characterized by a rise and fall and has a finite duration.

Pulsed Logic
-a signal modification that produces output independently of input signal duration. Pulse duration (dwell) is usually adjustable. Also referred to as one-shot logic. Pulsed logic may be immediate or delayed.

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