Glossary of Terms

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Absolute Pressure Transducer: A transducer which measures pressure in relation to zero pressure (a vacuum on one side of the diaphragm).

Absolute Pressure: Gage pressure plus atmospheric pressure.

Absolute Zero: Temperature at which thermal energy is at a minimum. Defined as 0 Kelvin, calculated to be -273.15°C or -459.67°F.

ac: Alternating current; an electric current that reverses its direction at regularly recurring intervals.

Acceleration: A change in the velocity of a body or particle with respect to time. The parameter that an accelerometer measures (dv/dt). Units expressed in "g".

Accelerometer: A device which converts the effects of mechanical motion into an electrical signal that is proportional to the acceleration value of the motion. A sensor. A transducer.

Accuracy: The closeness of an indication or reading of a measurement device to the actual value of the quantity being measured. Usually expressed as ą percent of full scale output or reading.

ADC: Analog-to-Digital Converter: an electronic device which converts analog signals to an equivalent digital form, in either a binary code or a binary-coded-decimal code. When used for dynamic waveforms, the sampling rate must be high to prevent aliasing errors from occurring.

Aliasing: If the sample rate of a function (fs) is less than two times the highest frequency value of the function, the frequency is ambiguously presented. The frequencies above (fs/2) will be folded back into the lower frequencies producing erroneous data.

Ambient Compensation: The design of an instrument such that changes in ambient temperature do not affect the readings of the instrument.

Ambient Conditions: The conditions around the transducer (pressure, temperature, etc.).

Ambient Pressure: Pressure of the air surrounding a transducer.

Ambient Temperature: The average or mean temperature of the surrounding air which comes in contact with the equipment and instruments under test.

Ampere (amp): A unit used to define the rate of flow of electricity (current) in a circuit; units are one coulomb (6.25 x 108 electronics) per second.

Amplifier: A device which draws power from a source other than the input signal and which produces as an output an enlarged reproduction of the essential features of its input.

Amplitude Span: The Y-axis range of a graphic display of data in either the time or frequency domain. Usually a log display (dB) but can also be linear.

Amplitude: A measurement of the distance from the highest to the lowest excursion of motion, as in the case of mechanical body in oscillation or the peak-to-peak swing of an electrical waveform.

Analog Output: A voltage or current signal that is a continuous function of the measured parameter.

Analog-to-Digital Converter (A/D or ADC): A device or circuit that outputs a binary number corresponding to an analog signal level at the input.

Anemometer: An instrument for measuring and/or indicating the velocity of air flow.

ANSI: American National Standards Institute.

Application Program: A computer program that accomplishes specific tasks, such as word processing.

ASCII: American Standard Code for Information Interchange. A seven or eight bit code used to represent alphanumeric characters. It is the standard code used for communications between data processing systems and associated equipment.

ASME: American Society of Mechanical Engineers.

ASTM: American Society for Testing and Materials.

Asymmetry Potential: The potential developed across the glass membrane with identical solutions on both sides. Also a term used when comparing glass electrode potential in pH 7 buffer.

Asynchronous: A communication method where data is sent when it is ready without being referenced to a timing clock, rather than waiting until the receiver signals that it is ready to receive.

ATC: Automatic temperature compensation.

Auto-Zero: An automatic internal correction for offsets and/or drift at zero voltage input.

AWG: American Wire Gage.

Background Noise: The total noise floor from all sources of interference in a measurement system, independent of the presence of a data signal.

Bandwidth: A symmetrical region around the set point in which proportional control occurs.

Baud: A unit of data transmission speed equal to the number of bits (or signal events) per second; 300 baud = 300 bits per second.

Bipolar: The ability of a panel meter to display both positive and negative readings.

Bit: Acronym for binary digit. The smallest unit of computer information, it is either a binary 0 or 1.

BPS: Bits per second.

Breakdown Voltage Rating: The dc or ac voltage which can be applied across insulation portions of a transducer without arcing or conduction above a specific current value.

Bridge Resistance: See Input impedance and Output impedance.

BTU: British thermal units. The quantity of thermal energy required to raise one pound of water at its maximum density, 1 degree F. One BTU is equivalent to .293 watt hours, or 252 calories. One kilowatt hour is equivalent to 3412 BTU.

Buffer: 1. A storage area for data that is used to compensate for a speed difference, when transferring data from one device to another. Usually refers to an area reserved for I/O operations, into which data is read, or from which data is written.2. Any substance or combination of substances which, when dissolved in water, produces a solution which resists a change in its hydrogen ion concentration on the addition of an acid or alkali.

Burn-In: A long term screening test (either vibration, temperature or combined test) that is effective in weeding out infant mortalities because it simulates actual or worst case operation of the device, accelerated through a time, power, and temperature relationship.

Bus: Parallel lines used to transfer signals between devices or components. Computers are often described by their bus structure (i.e., S-100, IBM PC).

Byte: The representation of a character in binary. Eight bits.

Cal-Chekä: Method developed by Logic Beach for regular front end calibration of the data logging signal conditioning input section.  Precision trimmed and temperature stabilized references insure accurate input modules calibration.

Calibration: The process of adjusting an instrument or compiling a deviation chart so that its reading can be correlated to the actual value being measured.

Celsius (centrigrade): A temperature scale defined by 0°C at the ice point and 100°C at boiling point of water at sea level.

CFM: The volumetric flow rate of a liquid or gas in cubic feet per minute.

Chatter: The rapid cycling on and off of a relay in a control process due to insufficient bandwidth in the controller.

CMR (Common-Mode Rejection): The ability of a panel meter to eliminate the effect of AC or DC noise between signal and ground. Normally expressed in dB at dc to 60 Hz. One type of CMR is specified between SIG LO and PWR GND. In differential meters, a second type of CMR is specified between SIG LO and ANA GND (METER GND).

CMV (Common-Mode Voltage): The AC or DC voltage which is tolerable between signal and ground. One type of CMV is specified between SIG LO and PWR GND. In differential meters, a second type of CMV is specified between SIG HI or LO and ANA GND (METER GND).

Color Code: The ANSI established color code for thermocouple wires in the negative lead is always red. Color Code for base metal thermocouples is yellow for Type K, black for Type J, purple for Type E and blue for Type T.

Common Mode Rejection Ratio: The ability of an instrument to reject interference from a common voltage at its input terminals with relation to ground. Usually expressed in db (decibels).

Common Mode: The output form or type of control action used by a temperature controller to control temperature, i.e. on/off, time proportioning, PID.

Compensation: An addition of specific materials or devices to counteract a known error.

Complex Wave: The resultant form of a number of sinusoidal waves that are summed together forming a periodic wave. Such waves may be analyzed in the frequency domain to readily determine their component parts.

Conductance: The measure of the ability of a solution to carry an electrical current. (See Equivalent Conductance)

Conduction: The conveying of electrical energy or heat through or by means of a conductor.

Convection: 1. The circulatory motion that occurs in a fluid at a non-uniform temperature owing to the variation of its density and the action of gravity. 2. The transfer of heat by this automatic circulation of fluid.

Counts: The number of time intervals counted by the dual-slope A/D converter and displayed as the reading of the panel meter, before addition of the decimal point.

CPS: Cycles per second; the rate or number of periodic events in one second, expressed in Hertz (Hz).

CSA: Canadian Standards Administration.

Current Proportioning: An output form of a temperature controller which provides a current proportional to the amount of control required. Normally is a 4 to 20 milliamp current proportioning band.

Current: The rate of flow of electricity. The unit of the ampere (A) defined as 1 ampere = 1 coulomb per second.

Cycle Time: The time usually expressed in seconds for a controller to complete one on/off cycle.

dB (Decibel): 20 times the log to the base 10 of the ratio of two voltages. Every 20 dBs correspond to a voltage ratio of 10, every 10 dBs to a voltage ratio of 3.162. For instance, a CMR of 120 dB provides voltage noise rejection of 1,000,000/1. An NMR of 70 dB provides voltage noise rejection of 3,162/1.

DC: Direct current; an electric current flowing in one direction only and substantially constant in value.

Decimal: Refers to a base ten number system using the characters 0 through 9 to represent values.

Density: Mass per unit of volume of a substance. I.E.: grams/cu.cm. or pounds/cu.ft.

Deviation: The difference between the value of the controlled variable and the value at which it is being controlled.

Diaphragm: The sensing element consisting of a membrane which is deformed by the pressure differential applied across it.

Differential Input: A signal-input circuit where SIG LO and SIG HI are electrically floating with respect to ANALOG GND (METER GND, which is normally tied to DIG GND). This allows the measurement of the voltage difference between two signals tied to the same ground and provides superior common-mode noise rejection.

Differential Pressure: The difference in static pressure between two identical pressure taps at the same elevation located in two different locations in a primary device.

Differential: For an on/off controller, it refers to the temperature difference between the temperature at which the controller turns heat off and the temperature at which the heat is turned back on. It is expressed in degrees.

Digital-to-Analog Converter (D/A or DAC): A device or circuit to convert a digital value to an analog signal level.

Displacement: The measured distance traveled by a point from its position at rest. Peak to peak displacement is the total measured movement of a vibrating point between its positive and negative extremes. Measurement units expressed as inches or millinches.

DMA: Acronym direct memory access. A high speed data storage mode of the IBM PC.

Drift: A change of a reading or a set point value over long periods due to several factors including change in ambient temperature, time, and line voltage.

Duty Cycle: The total time to one on/off cycle. Usually refers to the on/off cycle time of a temperature controller.

Electromotive Force (emf): The potential difference between the two electrodes in a cell. The cell emf is the cell voltage measured when no current is flowing through the cell. It can be measured by means of a pH meter with high input impedance.

EMF: Electromotive force. A rise in (electrical) potential energy. The principal unit is the volt.

EMI: Electromagnetic interference.

Environmental Conditions: All conditions in which a transducer may be exposed during shipping, storage, handling, and operation.

Eprom: Erasable Programmable Read-Only Memory. The PROM can be erased by ultraviolet light or electricity.

Excitation: The external application of electrical voltage current applied to a transducer for normal operation.

Fahrenheit: A temperature scale defined by 32° at the ice point and 212° at the boiling point of water at sea level.

Firmware: Programs stored in PROMs.

Floppy Disk: A small, flexible disk carrying a magnetic medium in which digital data is stored for later retrieval and use.

Flow Rate: Actual speed or velocity of fluid movement .

Flow: Travel of liquids or gases in response to a force (i.e. pressure or gravity).

Flowmeter: A device used for measuring the flow or quantity of a moving fluid.

FPM: Flow velocity in feet per minute.

FPS: Flow velocity in feet per second.

Freezing Point: The temperature at which the substance goes from the liquid phase to the solid phase.

Frequency Output: An output in the form of frequency which varies as a function of the applied input.

Frequency: The number of cycles over a specified time period over which an event occurs. The reciprocal is called the period.

Full Bridge: A Wheatstone bridge configuration utilizing four active elements or strain gages.

Full Scale Output: The algebraic difference between the minimum output and maximum output.

Gage Pressure Transducer: A transducer which measures pressure in relation to the ambient pressure.

Gage pressure: Absolute pressure minus local atmospheric pressure.

Gain: The amount of amplification used in an electrical circuit.

GPH: Volumetric flow rate in gallons per hour.

GPM: Volumetric flow rate in gallons per minute.

Ground: 1. The electrical neutral line having the same potential as the surrounding earth. 2. The negative side of DC power supply. 3. Reference point for an electrical system.

Grounded Junction: A form of construction of a thermocouple probe where the hot or measuring junction is in electrical contact with the sheath material so that the sheath and thermocouple will have the same electrical potential.

Half Bridge: Two active elements or strain gages.

Hertz (Hz): Units in which frequency is expressed. Synonymous with cycles per second.

HyperNetä:  The icon-based programming environment of HyperWare.  Connect icons together forming the program that runs within the data logger.  Choose from up to 32 different icons representing, sample rate clocks, math, logic, operational, data reduction and scheduling functions.

HyperCommä:  The communications environment of HyperWare.   Allows for RS-232, modem, Ethernet and RF link communications.

HyperWare Plotter:   Built-in plotter within the HyperWare software program.  Provides graphical plotting of up to 7 channels, with full zoom, and x and y-axis control.  Minimum, maximum, averages and integral view instantly available.

HyperTrackä:  The real-time display environment of HyperWare.  Provides real-time scrolling of actual data or plotting of data on a connected PC.

HyperWareä: The graphic software environment developed by Logic Beach to work with Logic Beach data logging and alarming systems.  Provides an easy-to-use icon-based programming environment for communications, programming, real-time trending and data post-processing.   File conversion to text and Excel utility also included. Runs under all current Windows operation systems.

Hysteresis: The difference in output when the measurand value is first approached with increasing and then with decreasing values. Expressed in percent of full scale during any one calibration cycle. See also Deadband.

Icon: A graphic functional symbol display used in HyperWare for communications, programming, real-time viewing and more. A graphic representation of a function or functions to be performed by the computer.

Impedance: The total opposition to electrical flow (resistive plus reactive).

Infrared: An area in the electromagnetic spectrum extending beyond red light from 760 nanometers to 1000 microns (106 nm). It is the form of radiation used for making non-contact temperature measurements.

Input Impedance: The resistance measured across the excitation terminals of a transducer.

Intrinsically Safe: An instrument which will not produce any spark or thermal effects under normal or abnormal conditions that will ignite a specified gas mixture.

Junction: The point in a thermocouple where the two dissimilar metals are joined.

K: When referring to memory capacity, two to the tenth power (1024 in decimal notation).

Kilowatt (kw): Equivalent to 1000 watts.

Kilowatt Hour (kwh): 1000 watthours. Kilovolt amperes (kva): 1000 volt amps.

KVA: Kilovolt amperes (1000-volt amps).

Large Scale Integration (LSI): The combining of about 1,000 to 10,000 circuits on a single chip. Typical examples of LSI circuits are memory chips and microprocessor.

Life Cycle: The minimum number of pressure cycles the transducer can endure and still remain within a specified tolerance.

Linearity: The closeness of a calibration curve to a specified straight line. Linearity is expressed as the maximum deviation of any calibration point on a specified straight line during any one calibration cycle.

Load Impedance: The impedance presented to the output terminals of a transducer by the associated external circuitry.

Load: The electrical demand of a process expressed as power (watts), current (amps) or resistance (ohms).

Loop Powered Sensor:  Sensor which acquires it power from a series DC power source and produces a 4-20mA output proportional to the rated scale of the sensor. 

Loop Resistance: The total resistance of a thermocouple circuit caused by the resistance of the thermocouple wire. Usually used in reference to analog pyrometers which have typical loop resistance requirements of 10 ohms.

LS-TTL Compatible: For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5 V which can source 20 ľA, and a logic 0 is obtained for inputs of 0 to 0.8 V which can sink 400 ľA. For digital output signals, a logic 1 is represented by 2.4 to 5.5 V with a current source capability of at least 400 ľA; and a logic 0 is represented by 0 to 0.6 V with a current sink capability of at least 16 MA. "LS" stands for low-power Schottky.

M: Mega; one million. When referring to memory capacity, two to the twentieth power (1,048,576 in decimal notation).

Mass Flow Rate: Volumetric flowrate times density, i.e. pounds per hour or kilograms per minute.

Mass Storage: A device like a disk or magtape that can store large amounts of data readily accessible to the central processing unit.

Maximum Operating Temperature: The maximum temperature at which an instrument or sensor can be safely operated.

Maximum Power Rating: The maximum power in watts that a device can safely handle.

Measuring Junction: The thermocouple junction referred to as the hot junction that is used to measure an unknown temperature.

Microamp: One millionth of an ampere, 10-6 amps, ľA.

Micron: One millionth of a meter, 10-6 meters.

Microvolt: One millionth of a volt, 10-6 volts.

Mil: One thousandth of an inch (.001").

Milliamp: One thousandth of an amp, 10-3 amps, symbol mA.

Millimeter: One thousandth of a meter, symbol mm.

Millivolt: Unit of electromotive force. It is the difference in potential required to make a current of 1 millampere flow through a resistance of 1 ohm; one thousandth of a volt, symbol mV.

Modem: Modulator/Demodulator. A device that transforms digital signals into audio tones for transmission over telephone lines, and does the reverse for reception.

ModuLogger:  A modular data logging system from Logic Beach in which additional expansion modules may be added in the field to increase channel count, functionality or power source.

Mueller Bridge: A high-accuracy bridge configuration used to measure three-wire RTD thermometers.

Multiplex: A technique which allows different input (or output) signals to use the same lines at different times, controlled by an external signal. Multiplexing is used to save on wiring and I/O ports.

N/C (No Connection): A connector point for which there is no internal connection.

Negative Temperature Coefficient: A decrease in resistance with an increase in temperature.

NEMA-4: A standard from the National Electrical Manufacturers Association, which defines enclosures intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, and hose-directed water.

NEMA-7: A standard from the National Electrical Manufacturers Association, which defines explosion-proof enclosures for use in locations classified as Class I, Groups A, B, C or D, as specified in the National Electrical Code.

NEMA-12: A standard from the National Electrical Manufacturers Association, which defines enclosures with protection against dirt, dust, splashes by non-corrosive liquids, and salt spray.

Network: A group of computers that are connected to each other by communications lines to share information and resources.

NMR (Normal-Mode Rejection): The ability of a panel meter to filter out noise superimposed on the signal and applied across the SIG HI to SIG LO input terminals. Normally expressed in dB at 50/60 Hz.

Normal-mode Rejection Ratio: The ability of an instrument to reject interference usually of line frequency (50-60 Hz) across its input terminals.

Offset: The difference in temperature between the set point and the actual process temperature. Also, referred to as droop.

Operational pH: The determination of sample pH by relating to pH measurements in a primary standard solution. This relationship assumes that electrode errors such as sensitivity and changes in asymmetry potential can be disregarded or compensated for, provided the liquid junction potential remains constant between standard and sample.

Optical Isolation: Two networks which are connected only through an LED transmitter and photoelectric receiver with no electrical continuity between the two networks.

Output Impedance: The resistance as measured on the output terminals of a pressure transducer.

Parallel Transmission: Sending all data bits simultaneously. Commonly used for communications between computers and printer devices.

pH Junctions: The Junction of a reference electrode or combination electrode is a permeable membrane through which the fill solution escapes (called the liquid junction).

Platinum 6% Rhodium: The platinum-rhodium alloy used as the negative wire in conjunction with platinum-30% rhodium to form a Type B thermocouple.

Platinum 10% Rhodium: The platinum-rhodium alloy used as the positive wire in conjunction with pure platinum to form a Type S thermocouple.

Platinum 13% Rhodium: The platinum-rhodium alloy used as the positive wire in conjunction with pure platinum to form a Type R thermocouple.

Platinum 30% Rhodium: The platinum-rhodium alloy used as the positive wire in conjunction with platinum 6% rhodium to form a Type B thermocouple.

Platinum 67: To develop thermal emf tables for thermocouples, the National Bureau of Standards paired each thermocouple alloy against a pure platinum wire (designated Platinum 2 prior to 1973, and currently Platinum 67). The thermal emf's of any alloy combination can be determined by summing the "vs. Pt-67" emf's of the alloys, i.e., the emf table for a Type K thermocouple is derived from the Chromel vs. Pt-67 and the Alumel vs. Pt-67 values.

Platinum: A noble metal which in its pure form is the negative wire of Type R and Type S thermocouples.

Polarity: In electricity, the quality of having two oppositely charged poles, one positive one negative.

Positive Temperature Coefficient: An increase in resistance due to an increase in temperature.

Potentiometer: 1. A variable resistor often used to control a circuit. 2. A balancing bridge used to measure voltage.

PPM: Abbreviation for "parts per million," sometimes used to express temperature coefficients. For instance, 100 ppm is identical to 0.01%.

Proof Pressure: The specified pressure which may be applied to the sensing element of a transducer without causing a permanent change in the output characteristics.

Protocol: A formal definition that describes how data is to be exchanged.

PSIA: Pounds per square inch absolute. Pressure referenced to a vacuum.

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

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

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

Random Access Memory (RAM): Memory that can be both read and changed during computer operation. Unlike other semi-conductor memories, RAM is volatile-if power to the RAM is disrupted or lost, all the data stored is lost.

Range: Those values over which a transducer is intended to measure, specified by its upper and lower limits.

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

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.

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

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

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

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.

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.

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

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

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.

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.

Resistance Ratio Characteristic: For thermistors, the ratio of the resistance of the thermistor at 25°C to the resistance at 125°C.

Resistance Temperature Characteristic: A relationship between a thermistor's resistance and the temperature.

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.

Resolution: The smallest detectable increment of measurement. Resolution is usually limited by the number of bits used to quantize the input signal. For example, a 12-bit A/D can resolve to one part in 4096 (2 to the 12 power equals 4096).

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.

RFI: Radio frequency interference.

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.

Room Conditions: Ambient environmental conditions under which transducers must commonly operate.

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

RTD: Resistance temperature detector.

Sample Rate Clock: Icon in HyperWare that determines frequency at which the inputs of a data logger are sampled and data extracted.  A required icon in any NET program.

Sensing Element: That part of the transducer which reacts directly in response to the input.

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

Sensitivity: The minimum change in input signal to which an instrument can respond.

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.

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

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.

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

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

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.

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

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

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.

Stagnation Pressure: The sum of the static and dynamic pressure.

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.

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.

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

Steady State Vibration: That condition of vibration induced by an unchanging continuing periodic force.

Stiffness: The ratio of the force required to create a certain deflection or movement of a part expressed as (Force/deflection) lbs/in or grams/cm.

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.

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.

Syntax: The rules governing the structure of a language.

TEMPCO: Abbreviation for "temperature coefficient": the error introduced by a change in temperature. Normally expressed in %/°C or ppm/°C.

Temperature Error: The maximum change in output, at any measurand value within the specified range, when the transducer temperature is changed from room temperature to specified temperature extremes.

Temperature Range, Compensated: The range of ambient temperatures within which all tolerances specified for Thermal Zero Shift and Thermal Sensitivity Shift are applicable (temperature error).

Temperature Range, Operable: The range of ambient temperatures, given by their extremes, within which the transducer may be operated. Exceeding compensated range may require recalibration.

Terminal: An input/output device used to enter data into a computer and record the output.

Terminal Strip Adapter: I/O terminal strip in a HyperLogger where all connections are made for signals, power and alarms. 

Thermal Coefficient of Resistance: The change in resistance of a semiconductor per unit change in temperature over a specific range of temperature.

Thermal Conductivity: The property of a material to conduct heat in the form of thermal energy.

Thermal Gradient: The distribution of a differential temperature through a body or across a surface.

Thermistor: A temperature-sensing element composed of sintered semiconductor material which exhibits a large change in resistance proportional to a small change in temperature. Thermistors usually have negative temperature coefficients.

Thermocouple Type Material
(ANSI Symbol)
J Iron/Constantan
K CHROMEGAŽ/ALOMEGAŽ
T Copper/Constantan
E CHROMEGAŽ/Constantan
R Platinum/Platinum 13% Rhodium
S Platinum/Platinum 10% Rhodium
B Platinum 6% Rhodium/Platinum30% Rhodium
G* Tungsten/Tungsten 26% Rhenium
C* Tungsten 5% Rhenium/Tungsten 26% Rhenium
D* Tungsten 3% Rhenium/Tungsten 150 Rhenium
*Not ANSI symbols.

Thermocouple: The junction of two dissimilar metals which has a voltage output proportional to the difference in temperature between the hot junction and the lead wires (cold junction).

Transducer: A device (or medium) that converts energy from one form to another. The term is generally applied to devices that take physical phenomenon (pressure, temperature, humidity, flow, etc.) and convert it to an electrical signal.

Transient Vibration: A temporary vibration or movement of a mechanical system.

Transitional Flow: Flow between laminar and turbulent flow, usually between a pipe Reynolds number of 2000 and 4000.

Transmitter (Two-Wire): 1. A device which is used to transmit data from a sensor via a two-wire current loop. The loop has an external power supply and the transmitter acts as a variable resistor with respect to its input signal. 2. A device which translates the low level output of a sensor or transducer to a higher level signal suitable for transmission to a site where it can be further processed.

Triple Point (Water): The thermodynamic state where all three phases, solid, liquid, and gas may all be present in equilibrium. The triple point of water is .01°C.

True RMS: The true root-mean-square value of an AC or AC-plus-DC signal, often used to determine power of a signal. For a perfect sine wave, the RMS value is 1.11072 times the rectified average value, which is utilized for low-cost metering. For significantly non-sinusoidal signals, a true RMS converter is required.

TTL Unit Load: A load with TTL voltage levels, which will draw 40 ľA for a logic 1 and -1.6 mA for a logic 0.

TTL-Compatible: For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5 V which can source 40 ľA, and a logic 0 is obtained for inputs of 0 to 0.8 V which can sink 1.6 mA. For digital output signals, a logic 1 is represented by 2.4 to 5.5 V with a current source capability of at least 400 ľA; and a logic 0 is represented by 0 to 0.6 V with a current sink capability of at least 16 mA.

TTL: Transistor-to-transistor logic. A form of solid state logic which uses only transistors to form the logic gates.

Typical: Error is within plus or minus one standard deviation (ą1%) of the nominal specified value, as computed from the total population.

Undershoot: The difference in temperature between the temperature a process goes to, below the set point, after the cooling cycle is turned off and the set point temperature.

Ungrounded Junction: A form of construction of a thermocouple probe where the hot or measuring junction is fully enclosed by and insulated from the sheath material.

Velocity: The time rate of change of displacement; dx/dt.

Viscosity: The inherent resistance of a substance to flow.

Volt: The (electrical) potential difference between two points in a circuit. The fundamental unit is derived as work per unit charge-(V = W/Q). One volt is the potential difference required to move one coulomb of charge between two points in a circuit while using one joule of energy.

Voltage: An electrical potential which can be measured in volts.

Voltmeter: An instrument used to measure voltage.

Volume Flow Rate: Calculated using the area of the full closed conduit and the average fluid velocity in the form, Q = V x A, to arrive at the total volume quantity of flow. Q = volumetric flowrate, V = average fluid velocity, and A = cross sectional area of the pipe.

Wheatstone Bridge: A network of four resistances, an emf source, and a galvanometer connected such that when the four resistances are matched, the galvanometer will show a zero deflection or "null" reading.

Write: To record data in a storage device or on a data medium.