supply current being drawn when the pressure
sensor is at null.
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.
measurand values over which the sensor is intended
to measure, specified by the upper and lower
device that converts alternating current into
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.
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.
%-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
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.
Point-that position of the plunger at
which the contacts snap from the operated contact
position to the normal contact position.
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.
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.
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.
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.
Scan-the reflective scan technique that
uses a special reflector (retroreflector) to
return light along the same path it was sent.
Polarity Protection-circuitry, usually
a diode which prevents current from flowing
into the control in case of accidental mis-wiring
of the plus (+) or minus (-) terminals, preventing
damage to the unit.
alternating component of voltage from a rectifier
or generator. A slight fluctuation in the intensity
of a steady current.
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.
Conditions-ambient environmental conditions
under which sensors must commonly operate, which
have been established as follows:
25 + -10 %C (77 + - 18 degrees F).
humidity: 90% or less.
pressure: 26 to 32 inches Hg.
Tolerances closer than shown are frequently
specified for sensor calibration and test environments.
voltage drop appearing across a control device
that is fully turned On.
Technique-a method of scanning objects.
The two general categories are through and reflective
Control-a photoelectric control in which
all three phases of control - sensing, signal
conditioning, and output - occur in a single
Sensor-a proximity sensor in which all
three phases of control, sensing, signal conditioning,
and output, occur in a single device.
Distance-the maximum recommended distance
between the sensor and standard target at which
sensor will effectively and reliably detect
Element-that part of a sensor which
responds directly to changes in input pressure.
recommended distance between the sensor and
standard target at which sensor will effectively
and reliably detect the target.
Shift-a change in sensitivity resulting
from an environmental change such as temperature.
sensing element. The basic element that usually
changes some physical parameter to an electrical
Circuit-a circuit in which current has
only one path to follow.
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
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.
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
Double-Throw (SPDT)-switch which may
either make or break a circuit, depending on
how it is wired.
Single-Throw (SPST)-switch with only
one moving and one stationary contact. Available
either normally open (N.O.) or normally closed
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.
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.
Contamination-indoor locations, non-industrial
areas, office buildings.
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.
algebraic difference between limits of the pressure
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.
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.
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:
diameter of the circle inscribed on the active
surface of the sensitive face of the sensor,
times the rated operating distance, whichever
is the greater.
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.
Gage-a sensing device providing a change
in electrical resistance proportional to the
level of applied stress.
change of state of a materiel from solid to
vapor and back to solid without going through
a liquid state.
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
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.
Frequency-the actual number of targets
to which the sensor can respond in a given time
period, usually expressed as Hertz (cycles per
part or piece being detected.
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.).
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.
Error-the maximum change in output,
at any input pressure within the specified range,
resulting from a change in temperature.
Drift Chart-a chart illustrating sensor
operating variance due to changes in temperature.
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.
Film-a technology using vacuum deposition
of conductors and dielectric materials onto
a substrate (frequently silicon) to form an
Response-a control type that responds
to the change in input signal level. Plug-in
amplifiers are either threshold or transition
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.
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.
Delay Before Availability-also know
as False Pulse Protection. Outputs are turned
Off when power is first applied during this
Travel-the distance from the plunger
free position to the full overtravel point.
fully packaged, signal conditioned, compensated
and calibrated sensor.
Protection-circuitry to guard against
spikes induced on the supply lines by inductive
sources such as heavy motors or solenoids turning
On and Off.
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.
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
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).
transducer with a current loop output, typically
4 to 20 mA, enabling transmission of a signal
over a longer distance.
generic term for Transistor Logic which is used
extensively in digital electronics systems.
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.
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.
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.
Differential Pressure Sensor-a differential
pressure sensor requiring the greater input
pressure to be applied to a specified pressure
Sensor-a sensor with limited side and
front sensing capabilities.
Sensing Distance-sensing distance after
temperature range tolerance and manufacturers
tolerance are taken into account.
rate at which the position of a moving object
is changing. Velocity has two characteristics:
magnitude (speed) and direction.
= 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.
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.
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.