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Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

SAMA

Scientific Apparatus Makers Association issued SAMA Std, RC21-4-1966 covering resistance thermometer elements for industrial use. This standard covers platinum, nickel and copper resistance elements.

Secondary Junction

An unwanted connection between a pair of thermocouple wires tending to produce a signal representative of the secondary junction temperature rather than the measuring junction temperature.

Sensitivity

The smallest input that will provide a specified output.

Sensor Interchange Ability Accuracy

Basic manufacturing reproducibility of RTD, thermocouples and other sensors.

Servo

A system which forces a calibrated reference potentiometer to adjust itself to a setting which is directly related to an unknown signal. Most servo recorders place the reference potentiometer (slide wire) at the end of a stretchy string or gear train which also moves the pointer in an approximate relationship to the reference setting in the Rustrak writing system, the stylus – reference potentiometer – contact assembly are unitized. There is no error between potentiometer setting and the writing stylus which reflects itself in its superior repeatability.

Settling Time

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

Shield

A protective conductive covering that provides a least resistance path to ground for external radiated noise.

Shunt

A calibrated low resistance connected in parallel with the input terminals of an ammeter in order to enable measurement of wider range of currents. It can be internal or external; typically, external shunts are either 50 or 100 mV rated.

S.I.

System International, the new name for the Metric System, using the meter, gram and liter as units of distance, weight and volume.

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 span of a signal conditioner is ±2 VDC.

Single Ended Input

Amplifier with one input referenced to a Resistance/Capacitor or Diode/Resistor circuit used to dissipate transient energy peaks.

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 a 16 mA span of a 4-20 mA transmitter signal.

Spare

A connector point reserved for options, special, or other configurations. The point is identified by an (E#) for location on the electrical schematic.

Splice

The connection of the internal RTD lead wires to the external lead wires, often through a metal sleeve slightly larger than the sheath.

Stability

Changes in accuracy over a year’s time due to aging of components.

Sublimation Point

That temperature at which certain solids will pass to the vapor state without passing through the liquid state?

Super Cooling

The cooling of a liquid below its freezing point without separation of the solid phase.

Super Heating

Heating a substance above its normal boiling point without a change of phase taking place; as with superheated water under pressure of several atmospheres.

Suppressor

A passive device o limit the energy level allowed to pass through. A MOV (metal oxide varistor) is a noise suppressor.

Synchronous Motor

An AC motor whose speed is exactly proportional to the frequency of the applied alternating voltage.