Salt Effect (fx): The effect on the activity coefficient due to salts in the solution.

SAMA: Scientific Apparatus Makers Association. An association that has issued standards covering platinum, nickel, and copper resistance elements (RTDs).

SCR: Silicone controlled rectifier.

Scroll: To move all or part of the screen material up to down, left or right, to allow new information to appear.

SCSI: Small Computer System Interface.

Secondary Standard: pH buffer solutions which do not meet the requirements of primary standard solutions but provide coverage of the pH range not covered by primary standards. Used when the pH value of the primary standard is not close to the sample pH value.

Seebeck Coefficient: The derivative (rate of change) of thermal EMF with respect to temperature normally expressed as millivolts per degree.

Seebeck Effect: When a circuit is formed by a junction of two dissimilar metals and the junctions are held at different temperatures, a current will flow in the circuit caused by the difference in temperature between the two junctions.

Seebeck EMF: The open circuit voltage caused by the difference in temperature between the hot and cold junctions of a circuit made from two dissimilar metals.

Self Heating: Internal heating of a transducer as a result of power dissipation.

Sensing Element: The part of the transducer which reacts directly in response to the measurand.

Sensitivity: The ratio of change in transducer output to a change in the value of the measurand.

Sensitivity Shift: A change in slope of the calibration curve due to a change in sensitivity.

Serial transmission: Sending one bit at a time on a single transmission line. Compare with parallel transmission.

Server: A computer on a network that serves as a central repository for data and programs and which can be accessed over the network by other computers, which are called clients.

Set Point: The temperature at which a controller is set to control a system.

Settling Time: The time taken for the display to settle within one digit final value when a step is applied to the meter input.

Shear Modulus: The ratio of the shear stress and the angular shear distortion.

Shear Stress: Where normal stress is perpendicular to the designated plane, shear stress is parallel to the plane.

Shearing Strain: A measure of angular distortion also directly measurable, but not as easily as axial strain.

Sheath Thermocouple: A thermocouple made out of mineral-insulated thermocouple cable which has an outer metal sheath.

Shielded Pair: A pair of conductors that are wrapped with metallic foil to isolate the pair from electrical interference.

SHTTP: Secure-Hypertext Transfer Protocol, Security Protocols For The Internet.

Shunt Cal (R-Cal): The change in electrical output caused by placing a fixed resistor between the appropriate transducer terminals. Used "in the field" for quick calibration.

Sign Bit: The first bit in a dibit (group of two bits) in 2 binary, 1 quarternary (2B1Q) modulation. The sign bit determines if the voltage of the transmitted signal is positive or negative. The second bit is the magnitude bit, and it determines whether the voltage is positive or negative.

Signal Conditioner: A circuit module which offsets, attenuates, amplifies, linearizes and/or filters the signal for input to the A/D converter. The typical output signal conditioner is +2 V dc.

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, compensating, digitizing, and linearizing.

Signal: An electrical transmittance (either input or output) that conveys information.

SIMM: Single In Line Memory Module.

Simplex: One-way only communications.

Single Precision: The degree of numeric accuracy that requires the use of one computer word. In single precision, seven digits are stored, and up to seven digits are printed. Contrast with double precision.

Single-ended Input: A signal-input circuit where SIG LO (or sometimes SIG HI) is tied to METER GND. Ground loops are normally not a problem in AC-powered meters, since METER GND is transformer-isolated from AC GND.

Single-Plane (Static) Balancing Machine: A single plane balancing machine is a gravitational or centrifugal balancing machine that provides information for accomplishing single plane balancing.

SLIP: Serial Line Internet Protocol. SLIP is currently a de facto standard, commonly used for point-to-point serial communications.

Slope (Electrode Sensitivity, Span): See Nernst factor.

SMBus: Smart Management Bus.

SMT: Surface Mount Technology.

SMTP: Simple Mail Transfer Protocol. The Internet standard protocol for transferring electronic mail messages from one computer to another.

Software: Generally, programs loaded into a computer from external mass storage but also extended to include operating systems and documentation.

Solvation: Ions in solution are normally combined with at least one molecule of solvent. This phenomenon is termed solvation.

Source Code: A non-executable program written in a high-level language. A compiler or assembler must translate the source code into object code (machine language) that the computer can understand and process.

SP50: Standard Project (Committee #50).

Span: The algebraic difference between the limits of the range from zero to full scale.

Span Adjustment: The ability to adjust the gain of a process or strain meter so that a specified display span in engineering units corresponds to a specified signal span. For instance, a display span of 200°F may correspond to the 16 mA span of a 4-20 mA transmitter signal.

Specifications: The group of error limits within which each device will operate.

Specific Gravity: The ratio of mass of any material to the mass of the same volume of pure water at 4°C.

Specific Heat: The ratio of thermal energy required to raise the temperature of a body 1° to the thermal energy required to raise an equal mass of water 1°.

Spread Spectrum: This communications technique has been used in secure military systems for a number of years and is now becoming popular in commercial systems. This format involves transmitting information which has been multiplied by a pseudo-random noise (PN) sequence which essentially "spreads" it over a relatively wide frequency bandwidth. The receiver detects and uses the same PN sequence to "despread" the frequency bandwidth and decode the transmitted information. This communications technique allows greater signal density within a given transmission bandwidth and provides a high degree of signal encryption and security in the process.

Spurious Error: Random or erratic malfunction.

SSR: Solid state relay (see relay, solid state).

Stability: The quality of an instrument or sensor to maintain a consistent output when a constant input is applied.

Standard Electrode Potential (E0): The standard potential E0 of an electrode is the reversible emf between the normal hydrogen electrode and the electrode with all components at unit activity.

Standardization: a process of equalizing electrode potentials in one standardizing solution (buffer) so that potentials developed in unknown solutions can be converted to pH values.

Star Network: A network topology with a central hub and a number of remote terminals. Each remote is connected to the hub by a point-to-point network.

Static Calibration: A calibration recording pressure versus output at fixed points at room temperature.

Static Error Band: The error band applicable at room temperature.

Static Pressure: Pressure of a fluid whether in motion or at rest. It can be sensed in a small hole drilled perpendicular to and flush with the flow boundaries so as not to disturb the fluid in any way.

Static Router: A router whose routing table must be reprogrammed by the network manager every time there is a change made to the internet work.

Static Unbalance: Static unbalance is that condition of unbalance for which the central principal axis is displayed only parallel to the shaft axis.

Steady Flow: A flow rate in the measuring section of a flow line that does not vary significantly with time.

Stop Bit: A signal following a character or block that prepares the receiving device to receive the next character or block.

Strain Gage: A measuring element for converting force, pressure, tension, etc., into an electrical signal.

Strain: The ratio of the change in length to the initial unstressed reference length.

Subscriber: A customer of a telephone company or other communications carrier.

Subcriber Line: Data transmission capacity over conventional twisted pair telephone lines. ADSL is a contender for a major piece of the "information highway" pie and it promises to deliver telephone, television, and data services to your home over the existing telephone line.

Super Cooling: The cooling of a liquid below its freezing temperature without the formation of the solid phase.

Super Heating: 1. The heating of a liquid above its boiling temperature without the formation of the gaseous phase. 2. The heating of the gaseous phase considerably above the boiling-point temperature to improve the thermodynamic efficiency of a system.

Supervisory Information: Signaling information used to connect, maintain, and disconnect a telephone circuit.

Surge Current: A current of short duration that occurs when power is first applied to capacitive loads or temperature dependent resistive loads such as tungsten or molybdenum heaters-usually lasting no more than several cycles.

Suspension Effect: The source of error due to varied reference liquid junction potential depending upon whether the electrodes are immersed in the supernatant fluid or deeper in the sediment. Normally encountered with solutions containing resins or charged colloids.

Syntax: The rules governing the structure of a language.