Glossary S
Schottky diode: hot carrier diode. A diode using an aluminium-silicon junction in which carrier storage is negligible, leading to very fast on and off states and thus very fast switching speeds. The foward voltages is 0.3v.

Schematic:  Circuit Diagram.

Schmitt Trigger: A building block in which the input must be taken to about 70% of rail voltage before the output will change. The lower level for change is about 30%. This produces a gap and thus noise is prevented from entering.

Screen: The surface of the CRT upon which the visible pattern is produced -- the display area.

SCR: Silicone controlled rectifier.

Secondary: The output side of a transformer. A re-chargable battery such as a car batttery. Also called accumulater. The battery does not make electricity but simply stores energy in chemical form.

Self- bias: Bias developed from the supply rail due to circuit components and a dropper resistor rather than a separate battery.

Semiconductor: Material that is nether a conductor nor insulator. Its properties can be altered by a control voltage.

Sensitivity: A measure of the ability of a receiver to respond to weak signals.

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

Sequential Access: An access mode in which records are retrieved in the same order in which they were written. Each successive access to the file refers to the next record in the file.

Series: Resistors, cells, switches and batteries etc can be connected in series.

Series Resonant Circuit: A circuit in which the components are connected in series and capable of oscillating at a particular frequency. It exhibits minimum impedance at resonance.

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

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

Short-Circuit: An un-intended path that conducts electricity. Also called a "bridge" or "short" such as when solder from two tracks touch on a PC board.

Shunt: This generally means parallel connection.

SI: System Internationale. The name given to the standard metric system of units.

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

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 Generator: A circuit that produces a variable and controllable signal.

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.

Signal Generator: A device for injecting a signal into a circuit input; the circuit's output is then read by an oscilloscope.

Silicon Controlled Rectifier (SCR): A reverse blocking triode thyristor. A pnp device.

Sine Wave: A common curved wave shape that is mathematically defined.

Single pole switch: A switch in which only one circuit is controlled.

Single Shot: A signal measured by an oscilloscope that only occurs once (also called a transient event).

Single Sweep: A trigger mode for displaying one screenful of a signal and then stopping.

Slope: On a graph or an oscilloscope screen, the ratio of a vertical distance to a horizontal distance. A positive slope increases from left to right, while a negative slope decreases from left to right.

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

Solar cell: A cell that produces current under sunlight.

Solenoid: A coil of wire that is long compared to its diameter, through which a current will flow and produce a magnetic flux to push or pull a rod (called an armature).

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.

Span: The difference between the upper and lower limits of a range expressed in the same units as the range.

Spectral Filter: A filter which allows only a specific band width of the electromagnetic spectrum to pass, i.e., 4 to 8 micron infrared radiation.

Spectrum Analysis: Utilizing frequency components of a vibration signal to determine the source and cause of vibration.

Spectrum: The resolving of overall vibration into amplitude components as a function of frequency.

Spurious Error: Random or erratic malfunction.

Square Wave: A periodic wave that alternately assumes one of two fixed values (high and low) with the transition time between these two levels being negligible.

SSR: Solid state relay  

Stray capacitance: Unwanted capacitance - created by the proximity of other components.

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

Superheterodyne Receiver: The most widely used radio receiver in which the incoming signal is fed into a mixer and mixed with a signal from a local oscillator. The output produces an intermediate frequency that is amplified through an IF strip, detected by a diode and amplified in an audio amplifier.

Sweep: One horizontal pass of an oscilloscope's electron beam from left to right across the CRT screen.

Sweep Speed: Same as the time base.

Switch: A device for connecting and disconnecting power to a circuit.