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Flowmeter directory - Flow controllers terms Category: Electronics and Engineering > Industrial automation Date & country: 16/12/2007, UK Words: 713

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.

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.

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.

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

Spurious Error
Random or erratic malfunction.

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

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…

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

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°.

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

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.

SP50
Standard Project (Committee #50).

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

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.

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

SMT
Surface Mount Technology.

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

Slope (Electrode Sensitivity, Span)
See Nernst factor.

SMBus
Smart Management Bus.

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

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 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.

SIMM
Single In Line Memory Module.

Simplex
One-way only communications.

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.

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.

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.

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.

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

Shoe Size Conversion Table
No, this has nothing to do with physical measurement or control. Just found this on the Web and never understood the difference between American shoe sizes and the rest of the world.

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

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

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.

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

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.

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.

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

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

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

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

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

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.

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

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.

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

SCR
Silicone controlled rectifier.

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

RTD
Resistance Temperature Detector.

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

RS-423
A recommended standard published by the EIA to specify electrical signal levels of a serial interface. RS-423 uses unbalanced circuits and it designed to be used with the RS-499 mechanical specifications.

RS-422
A recommended standard published by the EIA to specify electrical signal levels of a serial interface. RS-422 uses balanced circuits and is designed to be used with the RS-499 mechanical specifications.

RS-232
A recommended serial standard that is frequently used to interface a DTE and a DCE.

Router
A device that connects two or more LANs and operates at OSI Model layers one through three. A router is able to select from among multiple paths to route a data packet through the network based on an address sent with the data.

ROM
Read Only Memory.

Root Mean Square (RMS)
Square root of the mean of the square of the signal taken during one full cycle.

Rise Time
The time required for a sensor or system to respond to an instantaneous step function, measured from the 10% to 90% points on the response waveforms.

Ring Network
A network topology that connects its terminals in a loop or ring.

RISC
Reduced Instruction Set Comuting.

Rheostat
A variable resistor.

Rigid Rotor
A rotor is considered rigid when it can be corrected in any two (arbitrarily selected) planes [see 'Correction (Balancing) Plane'] and after that correction, its unbalance does not significantly exceed the balancing tolerances (relative to the shaft axis) at any speed up to maximum operating speed and when running under conditions which approximate…

RFI
Radio frequency interference.

Reynolds Number
The ratio of inertial and viscous forces in a fluid defined by the formula Re = rVD/µ, where: r = Density of fluid, µ = Viscosity in centipoise (CP), V = Velocity, and D = Inside diameter of pipe.

Response Time (time constant)
The time required by a sensor to reach 63.2% of a step change in temperature under a specified set of conditions. Five time constants are required for the sensor to stabilize at 600 of the step change value.

Response Time
The length of time required for the output of a transducer to rise to a specified percentage of its final value as a result of a step change of input.

Resonant Frequency
The measurand frequency at which a transducer responds with maximum amplitude.

Resolution
The smallest change in mechanical input which produces a detectable change in the output signal.

Resistance
The resistance to the flow of electric current measured in ohms (1/2) for a conductor. Resistance is function of diameter, resistivity (an intrinsic property of the material) and length.

Repeatability
The ability of a transducer to reproduce output readings when the same measurand value is applied to it consecutively, under the same conditions, and in the same direction. Repeatability is expressed as the maximum difference between output readings as a percent of full scale.

Remote
Not hard-wired; communicating via switched lines, such as telephone lines. Usually refers to peripheral devices that are located a site away from the CPU.

Relay (Solid State)
A solid state switching device which completes or interrupts a circuit electrically with no moving parts.

Relay (Mechanical)
An electromechanical device that completes or interrupts a circuit by physically moving electrical contacts into contact with each other.

Register
A storage device with a specific capacity, such as a bit, byte or word.

Refractory Metal Thermocouple
A class of thermocouples with melting points above 3600°F. The most common are made from tungsten and tungsten/rhenium alloys Types G and C. They can be used for measuring high temperatures up to 4000°F (2200°C) in non-oxidizing, inert, or vacuum environments.

Reference Plane
Any plane perpendicular to the shaft axis to which an amount of unbalance is referred.

Reference Mark
Any diagnostic point or mark which can be used to relate a position during rotation of a part to its location when stopped.

Redox Potential
The potential developed by a metallic electrode when placed in a solution containing a species in two different oxidation states.

Reference Junction
The cold junction in a thermocouple circuit which is held at a stable known temperature. The standard reference temperature is 0°C (32°F). However, other temperatures can be used.

Recovery Time
The length of time which it takes a transducer to return to normal after applying a proof pressure.

Record
A collection of unrelated information that is treated as a single unit.

Real Time
The time interval over which the system temperature is sampled for the derivative function.

Read Only Memory (ROM)
Memory that contains fixed data. The computer can read the data, but cannot change it in any way.

Ratiometric Measurement
A measurement technique where an external signal is used to provide the voltage reference for the dual-slope A/D converter. The external signal can be derived from the voltage excitation applied to a bridge circuit or pick-off supply, thereby eliminating errors due to power supply fluctuations.

Rate time
The time interval over which the system temperature is sampled for the derivative function.

Rated Capacity
The maximum measurand that a transducer is designed to measure within its specification.

Rate Action
The derivative function of a temperature controller.

Rankine (°R)
An absolute temperature scale based upon the Fahrenheit scale with 180° between the ice point and boiling point of water. 459.67°R = 0°F.

Rangeability
The ratio of the maximum flowrate to the minimum flowrate of a meter.

Pulse Width Modulation
An output in the form of duty cycle which varies as a function of the applied measurand.

Pulse Code Modulation
A method of quantizing audio-range analog signals into a digital form for transmission in digital communications systems, or for processing in DSP. Effectively the same as analog-to-digital conversion.

Pull Plate
Load cell attachment which allows tension or compression force to be directed at the center line of a load cell through a threaded center hole.

PSIS
Pounds per square inch standard. Pressure referenced to a standard atmosphere.

PSIG
Pound per square inch gage. Pressure referenced to ambient air pressure.

PSID
Pounds per square inch differential. Pressure difference between two points.

PSI
Pounds per square inch.