Glossary of Terms: S

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Sample and Hold
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.
Sample Interval
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.
Sampling Rate
The rate at which input data is polled for information. The number of samples, or readings, per second of an analog signal.
Saturation
Condition in which any further change of input no longer results in a change of output.
Saturation Voltage
The voltage drop appearing across a control device that is fully turned On.
SCADA
Supervisory control and data acquisition - a large scale software package usually used to monitor and control a manufacturing process.
Scan
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.
Seebeck Effect
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.
Self-Calibrating
A data acquisition module with a stable on-board reference voltage that software can use for automatic recalibration.
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
(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.
Sensitivity Shift
A change in sensitivity resulting from an environmental change such as temperature, pressure, or humidity.
Sensor
A device that can detect a change in a physical quantity (light or pressure for example) and produce a corresponding electrical signal.
Serial Communication
Communication method where data is transferred one bit at a time.
Series Circuit
A circuit in which current has only one path to follow.
Servo
When a controller changes a process variable to move the process variable in response to a setpoint change, it is called a servo.
Setpoint
(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.
Setpoint Program
Individual ramps and soak segments needed to generate a required setpoint versus time profile.
Setpoint Ramp
Increase or decrease in setpoint that can be configured to occur over a time interval.
Setpoint Rate
Specific rate of change for local setpoint change.
Setpoint Tracking
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".
Settling Time
When a change in signal occurs, the time taken for the input or output channel to settle to its new value.
Shed Mode
Mode of local control that units will go to when there is shed from communication.
Shed Time
Represents the number of sample periods before instrument sheds from communications.
Shielded
Inductive sensor installation in which the coil is insensitive to surrounding metal. The sensor may be flush mounted in metal.
Shielded Sensor
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 operating characteristics.
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 0.007 second duration.
Short
Short circuit. Also to intentionally bypass part of a circuit with a jumper.
Short Circuit
Abnormal connection and relatively low resistance between two points of a circuit resulting in a flow of excess (often damaging) current between these two points.
Short Circuit Protection
Depending on the application, any sensor in our product range may be available with protection against short circuiting.
Signal
General term referring to a conveyor of information.
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. 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.
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.
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.
Simultaneous Sampling
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.
Sine Wave
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 interval.
Single-Ended Input
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 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.).
Slave
A networked device that is controlled by another (master) device.
Slew Rate
The maximum rate of change of an output signal.
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.
Snap Action
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.
Soak
To maintain the process variable at a desired value.
Soak Segment
Combination of soak setpoint (value) and soak duration (time) in setpoint programming.
Software Trigger
A programmed event, such as a specific key press or mouse click, that triggers data capture.
Solid-State Device
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.
Span
Algebraic difference between limits of the pressure range.
Specific Gravity
Ratio of weight or mass of a given volume of a substance to that of same volume of a standard at same temperature.
Specular Scan
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.
Spike
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.
Square Wave
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.
Stability
Ability of an instrument or sensor to maintain a constant output when a constant input is applied.
Standard Target
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.
Static Pressure
Steady state pressure applied to a device, or, for a differential pressure device, process pressure applied equally to both connections.
Steam
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.
Step Change
Change from value to value in a single increment in negligible time.
Stilling Well
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.
Strain Gage
A sensing device providing a change in electrical resistance proportional to the level of applied stress.
Strain Gauge
A sensor that experiences a change in resistance when it is stretched or strained. It is attached to the body subjected to the strain.
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.
Sublimation
Change of state of a materiel from solid to vapor and back to solid without going through a liquid state.
Successive Approximation
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 actual voltage.
Supply Current
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.
Supply Voltage
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
Surge
A large, momentary increase in the voltage on a power line.
Switch
Mechanical or electrical device that makes or breaks contacts to either complete or open an electrical circuit; can be automatic or manual.
Switching Current
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.
Switching Frequency
Actual number of targets to which the sensor can respond in a given time period, usually expressed as Hertz (cycles per second).
System
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.
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