A
Absolute Pressure Sensor
-a sensor which measures input pressure in relation to zero pressure (a total
vacuum on one side of the diaphragm).
Actuator
-mechanism of the switch or switch enclosure which operates the contacts.
Acceleration
-the rate of change of velocity. Acceleration has two characteristics: magnitude
and direction.
Accuracy
- a comparison of the actual output signal of a device to the true value of the
input pressure. The various errors (such as linearity, hysteresis, repeatability and
temperature shift)* attributing to the accuracy of a device are usually expressed
as a percent of full scale output (Span)
Alignment
-placing the emitter (light source) and receiver (photoreceiver or reflector) so as
to direct the maximum amount of light on the photosensor. At long distances,
when the light beam has widened, the receiver should be centered in the beam to
lessen the chance of the emitter and receiver drifting out of alignment due to
vibration or shock.
Alternating Current (AC)one that reverses at regularly recurring intervals of time and has alternately
positive and negative values.
Ambient
-in the area. 1) light-Light in the area of the photosensor, but not originating with
the control light source. Ambient light can adversely affect non-modulated control
operation, and should be screened, if possible, from the sensor; 2) Temperatureaverage temperature of surrounding medium such as water, air, or earth, into
which the heat of the equipment is dissipated.
Analog Output
-having the property of being continuously variable, as opposed to having
discrete states.
AND Logic
-an output is produced only when all inputs are present.
Analog Output
- an electrical output from a sensor that changes proportionately with any change
in input pressure.
Anode
-the switch contact connected to the positive terminal of the power supply.
Aperture
-most often an external cap (with a small opening) placed over the receiver lens
to help detect small objects. It lets even a small object block enough light to be
detected. Also, an internal aperture in most receivers reduces the effect of offaxis ambient light.
Arc
-one of several kinds of visible electrical discharge between separated contacts of
a switch. It is primarily a stream of electrons and is accompanied by incandescent
metal vapor.
Attenuation
-loss or reduction of beam intensity as a result of environmental factors, dust,
humidity, steam etc.
Auto Zeroing Technique
- a method used to automatically set the null point on a pressure sensor. This is
usually done by using a microprocessor to open a solenoid valve at a
predetermined time interval. This references atmospheric pressure to both sides
of the pressure sensor chip. The microprocessor reads the output voltage and
makes that the new null point. This method is used to eliminate errors due to null
offset and null temperature shift.
Auxiliary Actuator
-a mechanism, sold separately, to provide basic switches with easier means of
operation and adjustment and adapt switches to different operating motions by
supplying supplemental overtravel.
B
Basic Switch -a self contained switching unit. It can be used alone, gangmounted, built into assemblies or enclosed in metal housings.
Bifurcated Contact
-a movable or stationary contact which is forked or divided to provide two pairs
of mating contact surfaces connected in parallel, instead of a single pair of mating
surfaces.
Bidirectional Differential Pressure Sensor
-a differential pressure sensor allowing the greater input pressure to be applied to
either pressure port.
B.F.S.L. (Best Fit Straight Line)
-a method for defining linearity. A straight line placed on a sensor output curve
such that half the data points lie above and half below that line. The method for
determining B.F.S.L., is the sum of least squares.
Bridge Resistance
- see Input Impedance and Output Impedance.
Break
-to open an electrical circuit.
Break Distance
-the minimum distance between separated mating contacts in their fully open
position.
Burst pressure
-the specified pressure which will rupture the sensing element but not the sensor
case.
C
Cascade -to combine logic circuitry to get more complex logic or timing control.
(Inputs and outputs are wired in series.)
Calibration
-a test during which known values of Measurand are applied to the device under
test and corresponding output readings are recorded under specified conditions.
Calibration Curve
-a graphical representation of the calibration record.
Calibration Cycle
-the application of known values of Measurand and recording of corresponding
Output readings over the full or the specified portion of the Range, in an
ascending and descending direction.
Catalyst
-a substance which changes the rate of a chemical reaction but is itself not
changed. Switch contact material sometimes acts as a catalyst, accelerating the
formation of polymers on the contact surface.
Cathode
-the switch contact connected to the negative terminal of the power supply.
Characteristics
-This term is used by MICRO SWITCH in a restricted sense and refers only to
switch operating characteristics such as pretravel, operating force, etc.
Clean Air
-ideal conditions. Climate controlled or sterile area.
Chip
-a die (unpackaged semiconductor device) cut from a silicon wafer, incorporating
semiconductor circuit elements such as resistors, diodes, transistors, and/or
capacitors.
Compensation
-procedure of providing a supplemental device, circuit, or special materials to
conunteract known sources of error (e.g., ambient temperature change).
Compensation is often related to temperature compensation only.
Complementary Output
-both N.O. and N.C. outputs are available for use. A circuit that provides sink or
source capability with a single input. Output that can be both light operated and
dark operated. (Also known as 4-wire DC controls.)
Control
-the complete system; sensor, amplifier, output.
Control Base
-unit remote from sensor in which amplification and conditioning of the input
signal takes place. Usually contains a power supply and an output device.
Convergent Beam
-A variation of the diffuse scanning mode. A photoelectric control whose optical
system is key to its operation. It simultaneously focuses and converges a very
small, intense beam to a fixed-focal point in front of the control. The control is
essentially blind a short distance before and beyond this focal point. Convergent
beam scanning is used to detect the presence or absence of small objects while
ignoring nearby background surfaces.
Convertible Output
-output that can be wired either as Normally Open or Normally Closed, but not at
the same time.
Corrective Factor
-the mathematical factor that, when multiplied by the sensing distance of a given
sensor, will adjust sensing distance for the different metals being used as targets.
Current
-time value of movement of free electrons. One ampere equals one coulomb per
second. Conventional reference is opposite to direction of actual electron
movement.
Current Consumption
-the amount of current required to power a sensor or control (excluding load).
See supply current.
Current Sinking
-an output type such that when it is On, current flow is from the load into the
device's output, then to ground. Output is Normally High. The sensor "sinks"
current from the load through the sensor to ground. The load is connected
between the positive lead of the supply and the output lead of the sensor.
Current Sourcing
-an output type such that when it is On, current flow is from the device into the
load. Output is Normally Low. The sensor "sources" current to the load. The load
is connected between the output lead and the negative ground lead of the supply.
D
Dark Operated (D.O.) -control operating mode in which the output (load) is
energized when the light is blocked (retro/thru scan) or object not present
(diffuse), the photosensor is dark.
Dead Break
-Imperfect snap action in which the normally closed circuit of the switch opens
before the plunger reaches the operating point, or the normally open circuit
opens before the plunger reaches the release point.
Dead Make
-Imperfect snap action in which a switch fails to close its circuit when the plunger
reaches the operating or release point.
Diaphragm
-the membrane of material that remains after etching a cavity into the silicon
sensing chip. changes in input pressure cause the diaphragm to deflect.
Dielectric
-the term dielectric is almost synonymous with electrical insulation, which can be
considered the applied form of the dielectric.
Dielectric Breakdown
-rupture of insulation material when the electric stress exceeds the dielectric
strength of the material.
Dielectric Strength
-the maximum potential gradient that a material can withstand without rupture.
As a material property it usually is calculated by dividing the breakdown voltage
by the thickness of the material between a pair of test electrodes. The term often
is applied to switches to mean the maximum voltage a switch can withstand
between specified terminals or between terminals and ground without leakage
current exceeding a specified value.
Differential Pressure Sensor
-a sensor which is designed to accept simultaneously two independent pressure
sources. The output is proportional to the pressure difference between the two
sources.
Differential Travel
-the distance from the operating point to the release point.
Diffusion
-a thermochemical process whereby controlled impurities are introduced into the
silicon to define the piezoresistors. Compared to ion implantation, it has two
major disadvantages: 1) the maximum impurity concentration occurs at the
surface of the silicon rendering it subject to surface contamination, and making it
nearly impossible to produce buried piezoresistors; 2) control over impurity
concentrations and levels is about one thousand times poorer than obtained with
ion implantation.
Diffuse Scan
-a reflective scanning technique in which reflection from a near-by non-shiny
surface illuminates the photosensor in the receiver. Sometimes called proximity
scan because of the required nearness of the light source and photosensor to
reflecting surface. Also used to detect color contrast as in registration control.
Digital Circuit
-a circuit that has only two stable states, operating in the manner of a switch;
that is, it is either On or Off.
Digital Output
-output that is of only two stable states, appearing in the manner of a switch;
that is, it is either On or Off or High or Low (i.e., high voltage or low voltage).
Direct Current (DC)
-a unidirectional current in which changes in value are so small that they may be
neglected. As ordinarily used, the term designates a practically non-pulsating
current.
Disable
-to prevent the output despite an input signal. A wiring terminal for this purpose
is provided on most MICRO SWITCH control bases. The disabling circuit may
receive its signal from the current sinking output of a photoelectric logic card, or
modulated LED control, or from an electromechanical limit switch, etc. Disabling
is used to prevent false or unwanted signals from triggering the control.
Double Break Contacts
-(Twin break). This breaks the circuit in two places. Referred to as form Z
circuitry also.
Double-Pole Double Throw (DPDT)
-switches which make and break two separate circuits. This circuit provides a
normally open and normally closed contact for each pole.
Drift
-an undesired change in output over a period of time, which is not a function of
any input pressure change.
Drift of an Operating Characteristic
-an inexact term referring in a general way to the degree of instability of a
plunger force or travel characteristic under specified conditions and during a
specified number of cycles of switch operation.
Dry Circuit
-slang expression meaning a low energy circuit. Although many individuals and
groups have assigned current and voltage values to "dry circuits" there is at
present no general agreement as to what the values should be.
E
Effective Sensing Distance -the difference between nominal sensing distance
and the % manufacturing tolerance.
Electrical Life
-life of a switch under a specified combination of electrical load, actuation,
environment and criterion of failure. Synonymous with switch life.
Enable
-the opposite of disable. To allow output in response to an input signal. We often
speak of one light source-photoreceiver pair (the "gating" pair) enabling a second
pair (the "inspect" pair).
Enclosed Switch
-a basic switch unit (contact block) enclosed in a durable metal housing. The
enclosure protects the switching unit, provides mounting means, and fitting for
conduit connection.
End points
-the Outputs at the specified upper and lower limits of the Range.
Environment-Proof Switch
-a switch which is completely sealed to ensure constant operating characteristics.
Sealing normally includes and "O" ring on actuator shaft and fused glass-to-metal
terminal seals or complete potting and an elastomer plunger-case seal.
Erosion, Contact
-a general loss of material from one or both working surfaces of a pair of mating
contacts, as a result of switching an electrical load.
Error
-the algebraic difference between the indicated value and the true value of the
input pressure. Usually expressed in percent of full scale output, sometimes
expressed in percent of the sensor output reading.
Error Band
-the band of maximum deviations of the output values from a specified reference
line or curve due to those causes attributable to the sensor. Usually expressed as
"+ -% of full scale output." The error band should be specified as applicable over
at least two calibration cycles, so as to include repeatability, and verified
accordingly.
Excess Gain
-the ratio of optical power available at a given emitter-to-receiver range to the
minimum optical power required to trigger the receiver.
Excitation
-the external source of energy (e.g., electrical voltage or current) applied to a
sensor for its operation.
Explosion-Proof
-having the ability to contain an explosion within the sensor or housing if it were
to occur.
Explosion-Proof Switch
-a UL listed switch capable of withstanding an internal explosion of a specified gas
without ignition of surrounding gases.
Extreme Contamination
-coal bins, residue on lens.
F
Fall Time -a measure of the time required for the output voltage of a circuit to
change from a high voltage level to a low voltage level, once a level change has
started (90% to 10%).
False Pulse
-an improper change of state of the output, usually associated with Turn-Off or
Turn-On.
False Pulsing
-circuitry designed to clamp output Off until the power supply has time to reach
proper voltage level. Typically 200-500 msec.
False Pulse Protection
-circuitry designed to clamp output Off until the power supply has time to reach
proper voltage level. Typically 200-500 msec.
Fiber Optics
-transparent fibers of glass or plastic used for conducting and guiding light
energy. Fiber optics are used in photoelectrics as light pipes consisting of a
bundle of small optical fibers (glass) or single strand (plastic) housed inside a
flexible sheathing.
Force, Contact
-the force holding closed contacts together.
Force Differential
-the difference between the operating force and the release force.
Free Position of the Plunger
-the position of the plunger when there is no external force other than gravity
applied to it.
Frequency, Natural
-the frequency of free (not forced) oscillations of the sensing element of a fully
assembled sensor.
Frequency Output
-an output in the form of frequency which varies as a function of the applied
pressure.
Full Overtravel Force
-the force required to depress the plunger of a switch to the full overtravel point.
Full Overtravel Point
-that position of the plunger beyond which further overtravel would cause
damage to the switch or actuator.
Full Scale Output (Span)
-the algebraic difference between output curve end points (outputs at specified
upper and lower output limits).
G
Gage Factor -a measure of the ration of the relative change of resistance to the
relative change in length of a resistive strain sensor (strain gage).
Gage Pressure
-a form of differential pressure measurement in which atmospheric pressure is
used as a reference.
Gravity Unit
-one gravity unit (abbreviated g) is an acceleration of 32.2 feet per second per
second.
Ground
-a conducting path, intentional or accidental, between an electric circuit or
equipment and the earth, or some large conducting body serving in place of the
earth (a voltage reference).
H
Hall Effect Technology -the description given to the following phenomena;
when a semiconductor, through which a current is flowing, is placed in a
magnetic field, a difference in potential (voltage) is generated between the two
opposed edges of the conductor in the direction mutually perpendicular to both
the field and the conductor. Typically used in sensing magnetic fields.
Hardwired
-physically interconnected and intended for a specific purpose. Hardwired logic is
essentially unalterable.
Hazardous Location
-defined as an area in which flammable or combustible mixtures are present.
Head-On
-a condition whereby the target approaches the sensing face of the proximity
sensor with its center along the sensing face.
High Contamination
-heavy particle laden air, extreme washdown environments, grain elevators.
Hermetically Sealed Switch
-a switch completely sealed to provide constant operating characteristics. All
junctures made with metal-to-metal or glass-to-metal fusion.
Hysteresis, Switching
-the principle associated with sensors, such that the operate point is not at the
same level as the release point. In solid state sensors, it is accomplished
electrically. In mechanical switches, it results from the storing of potential energy
before the transition occurs. Also known as differential, and is usually expressed
as a percentage of the operate point (e.g. 3-15%).
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 sourcephotoreceiver 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.
J
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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.
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.
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.
O
Off Delay Logic -adjustable delay (after input signal stops) before output is deenergized.
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.
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.
Q
Quiescent Supply Current -the supply current being drawn when the pressure sensor is at null.
R
Ratiometric (Ratiometricity Error) -at a given supply voltage, sensor output is a proportion
of that supply voltage. Ratiometricity error is the change in this proportion resulting from any change to the
supply voltage. Usually expressed as a percent of full scale output.
Range
-the measurand values over which the sensor is intended to measure, specified by the upper and lower
limits.
Rectifier
-a device that converts alternating current into direct current.
Reed Technology
-technology where the reed contacts are designed to be actuated by a magnet. When a magnetic field is
brought close to the reed contacts, the contacts are drawn together to make the circuit.
Reflective Scan
-a scanning technique in which the light source is aimed at a reflective surface to illuminate the photosensor.
Retroreflective, specular, diffuse scan and convergent beam are all reflective scan techniques.
Regulation %
-the ratio of voltage extremes due to loading or line fluctuations. The process of holding constant a quantity
such as voltage by means of a system that automatically corrects errors. For example, as more current is
drawn from a battery or power supply, the output voltage tends to decrease (load regulation). With a power
supply derived from AC, the DC output voltage can vary with the variation in AC voltage (line regulation).
Release Force
-the level to which force on the plunger must be reduced to allow the contacts to snap from the operated
contact position to the normal contact position.
Release Point
-that position of the plunger at which the contacts snap from the operated contact position to the normal
contact position.
Release Travel
-as an operating characteristic of a switch, release travel is the distance through which the plunger moves
when traveled from the release point to the free position. As a characteristic of the actuation applied to the
switch, release travel is the distance the plunger is released past the release point.
Repeatability
-the ability of a sensor to reproduce output readings when the same value is applied to it consecutively in
the same direction, for a specified number of cycles, or specified time duration.
Resolution
-the magnitude of output step changes as the pressure is continuously varied over the range. This term
applies primarily to potentiometric sensors. Resolution is best specified as average and maximum resolution.
Usually expressed in percent of full scale output.
Response Time
-the time it takes for a device to respond to an input signal. The sum of the sensor, amplifier, and output
response is the total response time.
Retroreflective Scan
-the reflective scan technique that uses a special reflector (retroreflector) to return light along the same path
it was sent.
Reverse Polarity Protection
-circuitry, usually a diode which prevents current from flowing into the control in case of accidental miswiring of the plus (+) or minus (-) terminals, preventing damage to the unit.
Ripple
-the alternating component of voltage from a rectifier or generator. A slight fluctuation in the intensity of a
steady current.
Rise Time
-a measure (10% to 90%) of the time required for an output voltage to rise from a state of low voltage to a
high voltage level, once a level change has started.
Room Conditions
-ambient environmental conditions under which sensors must commonly operate, which have been
established as follows: (a) Temperature: 25 + -10 %C (77 + - 18 degrees F). (b) Relative humidity: 90% or
less. (c) Barometric pressure: 26 to 32 inches Hg. Note: Tolerances closer than shown are frequently
specified for sensor calibration and test environments.
S
Saturation Voltage -the voltage drop appearing across a control device that is fully turned On.
Scan Technique
-a method of scanning objects. The two general categories are through and reflective scan.
Self-Contained Control
-a photoelectric control in which all three phases of control - sensing, signal conditioning, and output - occur
in a single device.
Self-Contained Sensor
-a proximity sensor in which all three phases of control, sensing, signal conditioning, and output, occur in a
single device.
Sensing Distance
-the maximum recommended distance between the sensor and standard target at which sensor will
effectively and reliably detect the target.
Sensing Element
-that part of a sensor which responds directly to changes in input pressure.
Sensitivity
-maximum recommended distance between the sensor and standard target at which sensor will effectively
and reliably detect the target.
Sensitivity Shift
-a change in sensitivity resulting from an environmental change such as temperature.
Sensor
-a sensing element. The basic element that usually changes some physical parameter to an electrical signal.
Series Circuit
-a circuit in which current has only one path to follow.
Shielded Sensor
-a sensor which "senses" only to the front of its face and ignores metals to its side. The presence of such
side metal, however, may cause a slight shift in operating characteristics.
Signal Conditioning
-to process the form or mode of a signal so as to make it intelligible to or compatible with, a given device,
including such manipulation as pulse shaping, pulse clipping, digitizing, and linearizing.
Signal Ratio
-1) broadly, the comparison of light seen by a photosensor when the beam is blocked to the light seen when
the beam is not blocked; 2) More specifically, the comparison of photocell resistance when sensor is dark to
when it is illuminated. Proper control application involves establishing a large dark-to-light ratio.
Single-Pole Double-Throw (SPDT)
-switch which may either make or break a circuit, depending on how it is wired.
Single-Pole Single-Throw (SPST)
-switch with only one moving and one stationary contact. Available either normally open (N.O.) or normally
closed (N.C.).
Shock, Mechanical
-a short pulse of acceleration, usually lasting only a few milliseconds. A typical shock test pulse is a half-sine
acceleration wave having 100g peak and .007 second duration.
Slide-By
-the condition whereby the target approaches the sensing face of the proximity sensor in such a direction
that its center will cross the axis of the sensing face at right angles.
Slight Contamination
-indoor locations, non-industrial areas, office buildings.
Snap Action
-in strict terms, snap action is a property of a switch such that the moving contact accelerates without added
travel of the plunger beyond that travel which was required to separate the contacts. National Electrical
Manufacturers Association defines snap action as "a rapid motion of the contacts from one position to
another position, or their return. This action is relatively independent of the rate of travel of the actuator."
The word "relatively" is important. In actual fact, the acceleration of the moving contact is partially
dependent upon the velocity of the plunger. The important point is that, once the plunger reaches the
operating or release point, the movable contact immediately transfers to its opposite position without further
travel of the plunger. A non-snap acting switch lacks this feature.
Span
-the algebraic difference between limits of the pressure range.
Specular Scan
-a reflective scan technique in which reflection from a shiny surface illuminates the photosensor, which must
be precisely positioned to receive the reflected light. The angle of incidence equals the angle of reflection.
Stability of an Operating Characteristic
-the extent to which an operating characteristic such as operating point remains constant during a specified
number of cycles of switch operation, under specified conditions of actuation, electrical loading and
environment. Most clearly expressed as a graph of the characteristic versus cycles of switch operation.
Standard Target
-an object used for making comparative measurements of operating distance. A square of mild steel, 1mm
thick. The length of the side of the square is equal to either: A: the diameter of the circle inscribed on the
active surface of the sensitive face of the sensor, or B: three times the rated operating distance, whichever
is the greater.
Storage Temperature Range
-the minimum and maximum specified temperature which may be applied to the pressure sensor without
causing a permanent change in the output characteristics.
Strain Gage
-a sensing device providing a change in electrical resistance proportional to the level of applied stress.
Sublimation
-the change of state of a materiel from solid to vapor and back to solid without going through a liquid state.
Supply Current
-units = Amps or milliamps. The amount of current necessary to maintain operation of a photoelectric
control, proximity sensor or control base. Sometimes referred to as Current Consumption.
Supply Voltage
-units + Volts. The range of power required to maintain proper operation of a photoelectric control, proximity
sensor or control base. The difference in potential (or range of difference in potential) necessary to operate
the unit.
Switching Frequency
-the actual number of targets to which the sensor can respond in a given time period, usually expressed as
Hertz (cycles per second).
T
Target -the part or piece being detected.
Terminal Base Linearity
-T.B.L. (End Point Linearity) - a method of defining linearity. The maximum deviation of any data point on a
sensor output curve from a straight line drawn between the end data points on that output curve. (T.B.L. is
approximately twice the magnitude of B.F.S.L.).
Terminal Line
-a theoretical slope for which the theoretical end points are normalized at 0 and 100% of both measurand
and output. Interchangeability error is referenced to this line.
Temperature Error
-the maximum change in output, at any input pressure within the specified range, resulting from a change in
temperature.
Thermal Drift Chart
-a chart illustrating sensor operating variance due to changes in temperature.
Thick-Film
-technology using silk screened pastes to form conductor, resistor, themistors, and insulator patterns;
screened onto the substrate (usually ceramic) and cured by firing at elevated temperatures.
Thin Film
-a technology using vacuum deposition of conductors and dielectric materials onto a substrate (frequently
silicon) to form an electrical circuit.
Threshold Response
-a control type that responds to the change in input signal level. Plug-in amplifiers are either threshold or
transition responsive.
Throw
-the number of circuits that each individual pole of a switch can control. The number of throws is completely
independent of the number of poles and number of breaks. A single-pole double-throw single-break switch
connects the common terminal of the switch to the normally closed terminal when the plunger is free, but
connects the common terminal to the normally open terminal when the plunger is depressed. A single-pole
single-throw single-break switch has a common terminal and either a normally open terminal or a normally
closed terminal but not both.
Thru Scan
-a scanning technique in which the emitter (light source) is aimed directly at the receiver. Also called direct
scan and transmitted scan, since light is transmitted directly, not reflected to the sensor. Presently, it is the
only scanning technique commonly used to scan distances greater than 40 feet.
Time Delay Before Availability
-also know as False Pulse Protection. Outputs are turned Off when power is first applied during this time
period.
Total Travel
-the distance from the plunger free position to the full overtravel point.
Transducer
-a fully packaged, signal conditioned, compensated and calibrated sensor.
Transient Protection
-circuitry to guard against spikes induced on the supply lines by inductive sources such as heavy motors or
solenoids turning On and Off.
Transients
-in electronic usage, usually refers to an unwanted, temporary, large increase or decrease in a current or
supply voltage that only occurs occasionally. Almost always due to reactive components during rapid
changes in voltage or current.
Transition Responsive
-a control type that responds to the rate of change in light intensity rather than the level change. Used to
detect fast moving objects that cause little change in light intensity level.
Translucent
-allows light to pass through. Detecting translucent objects is often best done with retroreflective scan,
during which the light must pass through the object twice, thereby causing more of a signal change (larger
signal ratio).
Transmitter
-a transducer with a current loop output, typically 4 to 20 mA, enabling transmission of a signal over a
longer distance.
TTL
-a generic term for Transistor Logic which is used extensively in digital electronics systems.
TTL Compatibility
-TTL (transistor-transistor-logic) requires NPN (current sinking) input signals. Reliable operation demands
maximum input sensor voltage drop of 0.8 V. Most TTL compatible interface devices have voltage drops of
less than 0.7V.
Typical
-(as used herein): refers to the target value or where a range is given, represents an estimate of where 2/3
of the total population of several production runs would be.
U
UL -Underwriter's Laboratories, Inc., a non-profit organization that establishes, maintains and operates
laboratories for the examination and testing of devices, systems and materials primarily for safety.
Unidirectional Differential Pressure Sensor
-a differential pressure sensor requiring the greater input pressure to be applied to a specified pressure port.
Unshielded Sensor
-a sensor with limited side and front sensing capabilities.
Usable Sensing Distance
-sensing distance after temperature range tolerance and manufacturers tolerance are taken into account.
V
Velocity -the rate at which the position of a moving object is changing. Velocity has two characteristics:
magnitude (speed) and direction.
Voltage
-units = Volts (DC) or Volts RMS (AC). The term used to designate the electrical energy, differential that
exists between two points and is capable of producing the flow of current when a closed path is connected
between the two points.
Voltage Drop
-units = Volts (DC) or Volts RMS (AC). Sometimes referred to as Saturation Voltage. In any solid state
control that switches a load, there will be some voltage dropped across the output. This voltage drop or
saturation voltage will often vary with the amount of current going through the output section and the load.
It should be specified with current conditions.
W
Welding, Contact -one of several conditions that may cause switch contacts to fail to separate at the
intended point of plunger travel. As the name implies, the contacts literally are welded together as a result of
the electrical and thermal effects at the contact interface.
X
Y
Z