-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) Temperature-average 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 off-axis 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.
[ Top of page] Basic
Switch -a self contained switching unit.
It can be used alone, gang-mounted, 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 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 -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.
[ Top of page] 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
-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.
[ Top of page] 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 -switches which make and break
two separate circuits. This circuit provides a
normally open and normally closed contact for
each pole.
Drift -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.
[ Top of page] -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 -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
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 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).
[ Top of page] 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).
[ Top of page] 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
-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%).
[ Top of page]
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