A component of a type of analog-to-digital converter. The analog signal is
frozen in a sample and hold circuit to prevent it changing during digitization.
The rate at which a controller samples the process variable, and calculates
a new output. Ideally, the sample interval should be set between 4 and 10 times
faster than the process dead time.
The rate at which input data is polled for information. The number of
samples, or readings, per second of an analog signal.
Condition in which any further change of input no longer results in a change
The voltage drop appearing across a control device that is fully turned On.
Supervisory control and data acquisition - a large scale software package
usually used to monitor and control a manufacturing process.
Normal channel scanning in a data acquisition system involves stepping round
and reading each input channel in turn. The scan will return to the first
channel once all the channels have been sampled.
The principle that describes how a thermocouple works. In a circuit in which
there are junctions between dissimilar metals, an electromotive force (voltage)
is set up when the junctions are at different temperatures.
A data acquisition module with a stable on-board reference voltage that
software can use for automatic recalibration.
A photoelectric control in which all three phases of control - sensing,
signal conditioning, and output - occur in a single device.
A proximity sensor in which all three phases of control, sensing, signal
conditioning, and output, occur in a single device.
The maximum recommended distance between the sensor and standard target at
which sensor will effectively and reliably detect the target.
That part of a sensor which responds directly to changes in input pressure.
(1) A measure of the minimum change in an input signal that an instrument
can detect. (2) Maximum recommended distance between the sensor and standard
target at which sensor will effectively and reliably detect the target.
Sensitivity Adjustment (Capacitive)
The sensing distance (SN) of the capacitive sensor may
be adjusted by means of a built-in potentiometer.
A change in sensitivity resulting from an environmental change such as
temperature, pressure, or humidity.
A device that can detect a change in a physical quantity (light or pressure
for example) and produce a corresponding electrical signal.
Communication method where data is transferred one bit at a time.
A circuit in which current has only one path to follow.
When a controller changes a process variable to move the process variable in
response to a setpoint change, it is called a servo.
(1) Desired value of the process variable. (2) Value of a controlled
variable, departure from which causes a controller to operate to reduce the
error and restore the intended steady state.
Individual ramps and soak segments needed to generate a required setpoint
versus time profile.
Increase or decrease in setpoint that can be configured to occur over a time
Specific rate of change for local setpoint change.
Local setpoint tracks PV or remote setpoint and uses that value when
transfer is made.
Set Zero Point
Control input to set a zero point at any point of the
resolution range of an absolute encoder, without mechanical
adjustment. In the case of programmable absolute encoders,
an offset value can also be set using "set zero point".
When a change in signal occurs, the time taken for the input or output
channel to settle to its new value.
Mode of local control that units will go to when there is shed from
Represents the number of sample periods before instrument sheds from
Inductive sensor installation in which the coil is
insensitive to surrounding metal. The sensor may be flush
mounted in metal.
A sensor which "sees" 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
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
0.007 second duration.
Short circuit. Also to intentionally bypass part of a circuit with a jumper.
Abnormal connection and relatively low resistance between two points of a
circuit resulting in a flow of excess (often damaging) current between these two
Short Circuit Protection
Depending on the application, any sensor in our product
range may be available with protection against short
General term referring to a conveyor of information.
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. Makes a signal suitable for input
to an analog-to-digital converter. For example, a signal may be filtered to
remove noise, or amplified to meet the range of the A-D converter.
(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
Silicon Controlled Rectifier (SCR)
A solid-state device that controls AC voltages to a load
within one cycle, by zero-cross or phase-angle firing.
When all analog signals are read simultaneously. This is achieved by
providing each input with its own A-D converter, and initiating sampling from a
single clock. It ensures that there is no reduction in sampling rate when more
signals are connected.
Waveform of a single frequency, indefinitely repeated in time. In practice
there must be a transient at the start and finish of such a wave.
Single Setpoint Ramp
Occurs between current local setpoint and final setpoint over a time
An analog input that is measured with respect to a common earth. Single
ended inputs are only suitable for signals that are of good size - 100 mV full
scale or above.
Single-Pole Double-Throw (SPDT)
Switch which may either make or break a circuit, depending on how it is
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.).
A networked device that is controlled by another (master) device.
The maximum rate of change of an output signal.
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.
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. NEMA 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.
To maintain the process variable at a desired value.
Combination of soak setpoint (value) and soak duration (time) in setpoint
A programmed event, such as a specific key press or mouse click, that
triggers data capture.
A device whose function is performed by semi-conductors or the use of
otherwise completely static components such as resistors and capacitors.
Sonic Beam Angle
The sonic beam angle defines the boundaries of the
emitted conical beam of ultrasonic sensors.
Algebraic difference between limits of the pressure range.
Ratio of weight or mass of a given volume of a substance to that of same
volume of a standard at same temperature.
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.
Short pulse of voltage or current - usually undesirable.
Split Range Control
Action in which two or more signals are generated or two or more final
control elements are actuated by an input signal.
Wave that alternates between two fixed values. Has very rapid (theoretically
zero) rise and fall times.
Stability (of an Operating Characteristic)
Extent to which an operating characteristic 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.
Ability of an instrument or sensor to maintain a constant output when a
constant input is applied.
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 the greater of (A) the diameter of the circle inscribed on the active surface
of the sensor's face, or (B) three times the rated operating distance.
Steady state pressure applied to a device, or, for a differential pressure
device, process pressure applied equally to both connections.
Steam is the gaseous form of water. Steam is actually "dry" in nature and
behaves as a gas. True steam is invisible to the naked eye. The plume seen above
a boiling pot is in fact water vapor and not steam.
Change from value to value in a single increment in negligible time.
A grounded metal tube with openings.
Storage Temperature Range
Minimum and maximum specified temperature which may be applied to a pressure
sensor without causing a permanent change in the output characteristics.
A sensing device providing a change in electrical resistance proportional to
the level of applied stress.
A sensor that experiences a change in resistance when it is stretched or
strained. It is attached to the body subjected to the strain.
When a material is distorted by forces acting on it, it is said to be
strained. Strain is the ratio of change in dimension to original dimension.
Change of state of a materiel from solid to vapor and back to solid without
going through a liquid state.
A technique used in A-D converters to measure an analog signal. It compares
the signal with progressively smaller values, each step getting nearer the
This is the maximum current consumed by the sensor, at
nominal voltage, exclusive of output. The amount of current
necessary to maintain operation of a photoelectric control,
proximity sensor or control base. Units = Amps or milliamps.
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. Units = Volts
A large, momentary increase in the voltage on a power line.
Mechanical or electrical device that makes or breaks contacts to either
complete or open an electrical circuit; can be automatic or manual.
The sum of the switching currents for the alarm output
and switching output must not exceed the specified maximum
switching current of the relevant output.
Actual number of targets to which the sensor can respond in a given time
period, usually expressed as Hertz (cycles per second).
Combination of several pieces of equipment to perform in a particular
manner. Set or arrangement so related or connected as to form a unity or
organized whole; collection of consecutive operations and procedures required to
accomplish an objective.