Flow Meter Glossary


Abrasive	–	Fluids are termed abrasive when they have a tendency to mechanically attack metals and parts made from other materials of construction.
AC	–	Alternating current; an electric current that reverses its direction at regularly recurring intervals.
Accuracy	–	The closeness of an indication or reading of a measurement device to the actual value of the quantity being measured. Usually expressed as ¬± percent of full-scale output or reading.
Acoustics	–	The degree of sound. The nature, cause, and phenomena of the vibrations of elastic bodies; which vibrations create compressional waves or wave fronts which are transmitted through various media, such as air, water, wood, steel, etc.
Adapter	–	A mechanism or device for attaching non-mating parts.
ADC	–	Analog-to-Digital Converter
Ambient Compensation	–	The design of an instrument such that changes in ambient temperature does 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 meets 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 (6.28 x 1018 electronics) per second.
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.
ATC	–	Automatic temperature compensation.
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.
Baud Rate	–	The transmission speed with which a terminal device will communicate with the master (and vice-versa) is determined by the baud rate. Terminal devices normally operate at 300 or 2400 baud.
Bearing	–	A part which supports a journal and in which a journal revolves.
Bernoulli's Equation	–	Describes the conservation of hydraulic energy across a constriction in a pipe. It states that the sum of the static energy (pressure head), kinetic energy (velocity head), and potential energy (elevation head) upstream and downstream of the constriction are equal.
Beta Ratio	–	The ratio of the diameter of a pipeline constriction to the unobstructed pipe diameter.
BNC	–	A quick disconnect electrical connector used to inter-connect and/or terminate coaxial cables.
BTU	–	British Thermal Units. The quantity of thermal energy required raising 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.
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).
Calibration	–	The process of adjusting an instrument so that its reading can be correlated to the actual value being measured.
Cavitation	–	The boiling of a liquid caused by a decrease in pressure rather than an increase in temperature.
CE Approval	–	CE marking is a declaration by the manufacturer that the product meets all the appropriate provisions of the relevant legislation implementing certain European Directives. The initials "CE" do not stand for any specific words but are a declaration by the manufacturer that his product meets the requirements of the applicable European Directive(s). Portaflow 330, 220A, 220B models manufactured in accordance with the following Directives and Standards
Center of Gravity (Mass Center)	–	The center of gravity of a body is that point in the body through which passes the resultant of weights of its component particles for all orientations of the body with respect to a uniform gravitational field.
Coanda Effect	–	Flow meters channel the flow stream in the flow meter so as to utilize this phenomenon that causes a fluid to attach itself to a surface. Feedback passages are used to alternately attach the fluid to each surface. Oscillating flows through the feedback passages can be related to the flow rate.
CFM	–	The volumetric flow rate of a liquid or gas in cubic feet per minute.
Closeness of Control	–	Total temperature variation from a desired set point of system. Expressed as "closeness of control" is ¬±2¬∞C or a system bandwidth with 4¬∞C, also referred to as amplitude of deviation.
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.
Communication	–	Transmission and reception of data among data processing equipment and related peripherals.
Compensated Connector	–	A connector made of thermocouple alloys used to connect thermocouple probes and wires.
Compensation	–	An addition of specific materials or devices to counteract a known error.
Conductivity	–	The electrical conductivity of a liquid is a measure of the ability of the liquid to conduct electricity (mS/cm). Note that water with few impurities (such as de-ionized water) is not very conductive, whereas water with impurities can be highly conductive.
Confidence Level	–	The range (with a specified value of uncertainty, usually expressed in percent) within which the true value of a measured quantity exists.
Connection Head	–	An enclosure attached to the end of a thermocouple, which can be cast iron, aluminum or plastic within which the electrical connections are made.
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.
Corrosive	–	Fluids are termed corrosive when they have a tendency to chemically attack metals and parts made from other materials of construction.
CPS	–	Cycles per second; the rate or number of periodic events in one second, expressed in Hertz (Hz).
Critical Damping	–	Critical damping is the smallest amount of damping at which a given system is able to respond to a step function without overshoot.
Critical Speed	–	The rotational speed of the rotor or rotating element at which resonance occurs in the system.
Cryogenic	–	Fluids are termed cryogenic when they operate at low temperatures, typically below approximately -75° C. Examples of these fluids include liquefied gases, such as oxygen and nitrogen.
Custody Transfer	–	Flow meters applied to custody transfer are used to buy and sell fluids, such as the measurement of natural gas between pipeline companies.
Damping	–	The reduction of vibratory movement through dissipation of energy. Types include viscous, coulomb, and solid.
Data Format	–	The M-Bus Data Format: Asynchronous, 11-bit character length (1 start bit, 8 data bits, 1 parity bit (even parity), 1 stop bit)
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.
Dead Volume	–	The volume of the pressure port of a transducer at room temperature and ambient barometric pressure.
Default	–	The value(s) or option(s) that are assumed during operation when not specified.
Degree	–	An incremental value in the temperature scale, i.e., there are 100 degrees between the ice point and the boiling point of water in the Celsius scale and 180¬∞F between the same two points in the Fahrenheit scale.
Density	–	Mass per unit of volume of a substance, e.g., the density of a fluid is its mass per unit volume (lb/ft3; kg/m3; g/cc). Specific gravity is a dimensionless number that represents the density of the liquid relative to water.
Deviation	–	The difference between the value of the controlled variable and the value at which it is being controlled.
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 Output	–	An output signal, which represents the size of an input in the form of a series of discrete quantities.
Digital-to-Analog Converter (D/A or DAC)	–	A device or circuit to convert a digital value to an analog signal level.
DIN (Deutsche Industrial Norm)	–	A set of German standards recognized throughout the world. The 1/8 DIN standard for panel meters specifies an outer bezel dimension of 96 x 48 mm and a panel cutout of 92 x 45 mm.
Doppler Effect	–	A phenomenon related to how sound is perceived from objects in motion, such as the horn of a moving car having a higher pitch moving towards a listener than it does when moving away.
Doppler Technology	–	An acoustic pulse is reflected back to the sensor from particles or gases in the flowing liquid. The flow rate of any fluid can be measured as long as it contains air bubbles or solids. It is ideal for wastewater, slurries, sludge and most chemicals, acids, caustics and lubrication fluids.
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.
Duplex	–	Pertaining to simultaneous two-way independent data communication transmission in both directions. Same as "full duplex".
Echo	–	To reflect received data to the sender. For example, keys depressed on a keyboard are usually echoed as characters displayed on the screen.
Electrical Interference	–	Electrical noise induced upon the signal wires that obscure the wanted information signal.
EMI	–	Electromagnetic interference
Emissivity	–	The ratio of energy emitted by an object to the energy emitted by a blackbody at the same temperature. The emissivity of an object depends upon its material and surface texture; a polished metal surface can have an emissivity around 0.2 and a piece of wood can have an emissivity around 0.95.
EN-1434	–	European standard for the measurement of energy, water or heat.
End Point (potentiometer)	–	The apparent equivalence point of a titration at which a relatively large potential change is observed.
Environmental Conditions	–	All conditions in which a transducer may be exposed during shipping, storage, handling, and operation.
Error	–	The difference between the value indicated by the transducer and the true value of the measured being sensed.
Explosion-proof Enclosure	–	An enclosure that can withstand an explosion of gases within it and prevent the explosion of gases surrounding it due to sparks, flashes or the explosion of the container itself, and maintain an external temperature which will not ignite the surrounding gases.
Exposed Junction	–	A form of construction of a thermocouple probe where the hot or measuring junction protrudes beyond the sheath material so as to be fully exposed to the medium being measured. This form of construction usually gives the fastest response time.
Fahrenheit	–	A temperature scale defined by 32¬∞ at the ice point and 212¬∞ at the boiling point of water at sea level.
Ferrule	–	A compressible tubular fitting that is compressed onto a probe inside a compression fitting to form a gas-tight seal.
Field Balancing Equipment	–	An assembly of measuring instruments for performing balancing operations on assembled machinery, which is not mounted in a balancing machine.
Field of View	–	A volume in space defined by an angular cone extending from the focal plane of an instrument.
File	–	A set of related records or data treated as a unit.
Flow	–	Travel of liquids in response to a force (i.e. pressure or gravity).
Flow Nozzle	–	A constriction consisting of a contoured plate that forms a hole for the flow stream that is sandwiched in the pipe between two flanges.
Flow Rate	–	Actual speed or velocity of fluid movement
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	–	The number of cycles over a specified time over which an event occurs. The reciprocal is called the period.
Frequency Output	–	An output in the form of frequency, which varies as a function of the applied input.
Frequency, Natural	–	The frequency of free (not forced) oscillations of the sensing element of a fully assembled transducer.
Full Scale Output	–	The algebraic difference between the minimum output and maximum output.
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.
Handshake	–	An interface procedure that is based on status/data signals that assure orderly data transfer as opposed to asynchronous exchange.
Hardware	–	The electrical, mechanical, and electromechanical equipment and parts associated with a computing system,
Heat	–	Thermal energy. Heat is expressed in units of calories or BTU’s.
Heat Sink	–	1. Thermodynamic. A body, which can absorb thermal energy. 2. Practical. A finned piece of metal used to dissipate the heat of solid-state components mounted on it.
Heat Transfer	–	The process of thermal energy flowing from a body of high energy to a body of low energy. Means of transfer are: conduction; the two bodies contact. Convection; a form of conduction where the two bodies in contact are of different phases, i.e. solid and gas. Radiation: all bodies emit infrared radiation.
Heat Treating	–	A process for treating metals where heating to a specific temperature and cooling at a specific rate changes the properties of the metal.
Hertz (Hz)	–	Units in which frequency is expressed. Synonymous with cycles per second.
Hydrocarbons	–	A general class of chemicals that contain hydrogen and carbon, such as natural gas, fuel oil and gasoline. They are often flammable.
ID	–	Inside diameter
Industrial Gases	–	Generally refers to pure gases that are commonly used industry, such as oxygen, nitrogen, argon, and helium.
Inferential Flow Measurement	–	Inferential flow meters do not measure volume, velocity or mass, but rather measure flow by inferring its value from other measured parameters. Examples of flow meter technologies that measure inferentially include differential pressure, target and variable area flow meters.
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.
Insulated Junction	–	See Ungrounded Junction
Insulation Resistance	–	The resistance measured between two insulated points on a transducer when a specific DC voltage is applied at room temperature.
Interchangeability Error	–	A measurement error that can occur if two or more probes are used to make the same measurement. It is caused by a slight variation in characteristics of different probes.
Interface	–	The means by which two systems or devices are connected and interact with each other.
Intrinsically Safe	–	An instrument, which will not produce any spark or thermal effects under normal or abnormal.
IP Rating	–	(or "Ingress Protection") ratings are defined in international standard EN 60529 (British BS EN 60529
IP66	–	First digit is the intrusion protection, in this case 6 is totally dust tight. Second digit is moisture protection, in this instance protection against string water jets and waves.
IP67	–	Total dust ingress protection and protected against temporary immersion between 15cm and 1m depth.
Isolation	–	The reduction of the capacity of a system to respond to an external force by use of resilient isolating materials.
Joule	–	The basic unit of thermal energy.
Junction	–	The point in a thermocouple where the two dissimilar metals are joined.
Kelvin	–	Symbol K. The unit of absolute or thermodynamic temperature scale based upon the Celsius scale with 100 units between the ice point and boiling point of water. 0¬∞C = 273.15K (there is no degree (¬∞) symbol used with the Kelvin scale).
Kilowatt (kW)	–	Equivalent to 1000 watts
Kilowatt Hour (kWh)	–	1000 watt-hours. Kilovolt amperes (kva)
Kinetic Energy	–	Energy associated with mass in motion, i.e., 1/2 rV2 where r is the density of the moving mass and V is its velocity.
Laminar Flow	–	Streamlined flows of fluid where viscous forces are more significant than inertial forces, generally below a Reynolds number of 2000.
Laminar Flow Element	–	An element constriction consisting of a tube bundle or parallel plates used to measure flows with low Reynolds numbers. The differential pressure across this flow meter is linear with flow.
Leakage Rate	–	The maximum rate at which a fluid is permitted or determined to leak through a seal. The type of fluid, the differential Limits of Error
Level Converter	–	An interface converter that converts the signals from a PC via the RS 232 interface to an M-Bus signal. This device supplies the M-Bus with the required voltage. The level converter is connected between the master and the terminal device.
Life Cycle	–	The minimum number of pressure cycles the transducer can endure and still remain within a specified tolerance.
Lightning Protection (power surge protection)	–	Under certain circumstances, it makes sense to install power surge protection for the M-Bus system components. The installation of power surge protection (observe local regulations) is definitely advisable for open cable routing.
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	–	The electrical demand of a process expressed as power (watts), current (amps) or resistance (ohms).
Load Impedance	–	The impedance presented to the output terminals of a transducer by the associated external circuitry.
Low-Loss Flow Tube	–	A low-loss flow tube is a constriction that is similar to a Venturi-tube, but with shorter inlet and outlet sections.
M	–	Mega; one million. When referring to memory capacity, two to the twentieth power (1,048,576 in decimal notation).
Magnetic Flow Meters	–	Also known as Mag Meter, is a volumetric flow meter which does not have any moving parts and is ideal for wastewater applications or any dirty liquid which is conductive or water based. Magnetic flow meters will generally not work with hydrocarbons, distilled water and many non-aqueous solutions). Magnetic flow meters are also ideal for applications where low pressure drop and low maintenance are required.
Mass Flow Measurement	–	Mass flow meters utilize techniques that measure the mass flow of the flowing stream. Examples of flow meter technologies that measure mass flow include Coriolis mass and thermal flow meters.
Mass Flow Rate	–	Volumetric flow rate times density, i.e. pounds per hour or kilograms per minute.
Master	–	A central M-Bus unit or a PC with read-out software is referred to as a master.
M-Bus Master	–	An M-Bus master is an "intelligent" level converter that independently reads the M-Bus modules (meters), and, if equipped to do so, can store their values in its own memory. The master supplies the M-Bus with the required voltage. Its memory can also be read out from a PC with the corresponding software.
Materials of Construction	–	The materials from which the parts of the equipment are fabricated. Parts that are exposed to the operating fluid are termed "wetted" parts.
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.
M-Bus Master	–	An M-Bus master is an "intelligent" level converter that independently reads the M-Bus modules (meters), and, if equipped to do so, can store their values in its own memory. The master supplies the M-Bus with the required voltage. Its memory can also be read out from a PC with the corresponding software.
Mean Temperature	–	The average of the maximum and minimum temperature of process equilibrium.
Method of Correction	–	A procedure whereby the mass distribution of a rotor is adjusted to reduce unbalance, or vibration due to unbalance, to an acceptable value. Adding material to, or removing it from, the rotor usually makes corrections.
Mica	–	A transparent mineral used as window material in high-temperature ovens.
Microamp	–	One millionth of an ampere, 10-6 amps, ¬µA
Micron	–	One millionth of a meter, 10-6 meters
Mil	–	One thousandth of an inch (0.001")
Millimeter	–	One thousandth of a meter, symbol mm
Modem	–	A modem enables data transmission of meter readings via the public phone network. Modems used in an M-Bus system must fully support the M-Bus format; i.e., the 11-bit format must be supported. Some of the latest modems work with a 10-bit format and cannot be used with M-Bus systems.
NB	–	Nominal Bore
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.
Node	–	Each individual system component in an M-Bus system is designated as a node. Each master, repeater, and each meter (terminal device) is a node.
Noise	–	An unwanted electrical interference on the signal wires.
O.D.	–	Outside Diameter
Offset	–	The difference in temperature between the set point and the actual process temperature. Also, referred to as droop.
Operating Principle	–	The M-Bus is based on the master-slave principle. The master sequentially requests one or several meters via the M-Bus module to send their data to it. Communication between the slaves is not possible. Data transmission on the M-Bus is carried out bidirectional, during which work ensues in the master-to-slave direction with voltage differences. An open-circuit voltage of 35V to 40V is applied to the repeater output as a logical 1 (mark). The logical 0 (space) corresponds to a voltage of -12V. In the other direction, from slave to master, current differences are used. Current consumption of approx. 1.5mA can be measured in the idle-circuit condition as a logical 1 for each slave. Logical 0 designates an increased current consumption of approx. 11-20mA.
Orifice Plate	–	A constriction consisting of a flat plate with a hole for the flow stream that is sandwiched in the pipe between two flanges.
Output	–	The electrical signal, which is produced by an applied input to the transducer.
Output Impedance	–	The resistance as measured on the output terminals of a pressure transducer.
Output Noise	–	The RMS, peak-to-peak (as specified) ac component of a transducer's DC output in the absence of a measured variation.
Parity	–	A technique for testing transmitting data. Typically, a binary digit is added to the data to make the sum of all the digits of the binary data either always even (even parity) or always odd (odd parity).
Phase	–	A time based relationship between a periodic function and a reference. In electricity, it is expressed in angular degrees to describe the voltage or current relationship of two alternating waveforms.
Polypropylene	–	A polymer of propylene used as a thermoplastic molding material. Does not soak up water, making it ideal for uses where it will be constantly subject to moisture.
PortaGraph Software	–	Portagraph II is a software application specifically written for use with Micronics flow meters which simplifies the downloading and viewing of the instrument‚ logged data. Data may also be viewed in text format or exported to Excel for analysis that is more detailed. Also allows real time monitoring, where measured data is automatically captured sample by sample and displayed in either graph or data table format. Data logged in one set of units can quickly be converted to another set if required.
Positive Temperature Coefficient	–	An increase in resistance due to an increase in temperature.
Potential Energy	–	Energy related to the position or height above a place to which fluid could possibly flow.
Power Supply	–	A separate unit or part of a circuit that supplies power to the rest of the circuit or to a system.
PPM	–	Abbreviation for "parts per million," sometimes used to express temperature coefficients. For instance, 100 ppm is identical to 0.01%.
Primary Address	–	Used for identification of the terminal device within the M-Bus system. If the primary address is used for identification, every terminal device must be provided with a different primary address between 1 and 250.
Primary Device	–	Part of a flow meter, which is mounted internally or externally to the fluid conduit and produces a signal corresponding to the flow rate and from which the flow may be determined.
Probe	–	A generic term that is used to describe many types of temperature sensors.
Process Meter	–	A panel meter with sizable zero and span adjustment capabilities, which can be scaled for readout in engineering units for signals such as 4-20 mA, 10-50 mA and 1-5 V.
Range	–	Those values over which a transducer is intended to measure, specified by its upper and lower limits.
Rangeability	–	The ratio of the maximum flow rate to the minimum flow rate of a meter.
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.
Real Time	–	The time interval over which the system temperature is sampled for the derivative function.
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.
Relay (mechanical)	–	An electromechanical device that completes or interrupts a circuit by physically moving electrical contacts into contact with each other.
Relay (solid-state)	–	A solid state-switching device, which completes or interrupts a circuit electrically with no moving parts.
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 measured 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.
Repeater	–	Serves for signal amplification on the M-Bus and is used for long line lengths.
Residual (Final) Unbalance	–	Residual unbalance is that unbalance of any kind that remains after balancing.
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.
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, e.g., RD = 3160 · Flow gpm · Specific Gravity / (Viscosity cP · Diameter inch)
Reynolds Number	–	A dimensionless number that is used to describe the flowing characteristics of the fluid. Operating a flow meter outside of its Reynolds number constraint can degrade accuracy and make some flow meters turn off.
RFI	–	Radio frequency interference
Sanitary	–	Sanitary piping systems and components are used where cleanliness is important, such as in the food and beverage, pharmaceutical and chemical industries.
Secondary Address	–	As with the primary address, the secondary address is used to identify the terminal device. If the secondary address is used, each terminal device must be provided with a different address. Normally, the terminal device's 8-digit serial number is used. In its entirety, the secondary address consists of the serial number, the manufacturer ID, version, and device type.
Secondary Device	–	A part of the flow meter, which receives a signal proportional to the flow rate, from the primary device, and displays, records and/or transmits the signal.
Segmental Wedge	–	A constriction consisting of a hill-like structure in the flow stream. It is often used for fluids that contain some solids or that are mildly abrasive.
Sensing Element	–	That part of the transducer, which reacts directly in response to the input.
Sensitivity	–	The minimum change in input signal to which an instrument can respond.
Sensitivity Shift	–	A change in slope of the calibration curve due to a change in sensitivity.
SI	–	System Internationale. The name given to the standard metric system of units.
Signal	–	An electrical transmittance (either input or output) that conveys information.
Slurry	–	Contains both liquid and solids, and are often used as a means to transport the solids.
Specific Gravity	–	A dimensionless number that represents the density of the liquid relative to water.
Spectrum	–	The resolving of overall vibration into amplitude components as a function of frequency.
SREC	–	Solar Renewable Energy Credit that can be sold or purchased (SRECs) based upon state.
Stability	–	The quality of an instrument or sensor to maintain a consistent output when a constant input is applied.
System Components	–	Devices such as the master, level converter, repeater, and modem, as well as terminal units with their own M-Bus modules are designated system components.
Temperature Error	–	The maximum change in output, at any measure and 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).
Terminal Devices	–	A unit with an M-Bus module that occupies a separate M-Bus addresses. A terminal device is often referred to as a slave.
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.
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) (refer to Seebeck emf).
Thomson Effect	–	When current flows through a conductor within a thermal gradient, a reversible absorption or evolution of heat will occur in the conductor at the gradient boundaries.
Time of Flight (TOF)	–	A variety of methods that measure the time that it takes for an object, particle or acoustic, electromagnetic or other wave to travel a distance through a medium. This measurement can be used for a time standard as a way to measure velocity or path length through a given medium, or as a way to learn about the particle or medium (such as composition or flow rate).
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.
Transducer Vibration	–	Generally, any device which converts movement, either shock or steady state vibration, into an electrical signal proportional to the movement; a sensor.
Transient Vibration	–	A temporary vibration or movement of a mechanical system.
Transit Time	–	A typical transit-time flow measurement system utilizes two ultrasonic transducers that function as both ultrasonic transmitter and receiver. The flow meter operates by alternately transmitting and receiving a burst of sound energy between the two transducers and measuring the transit time that it takes for sound to travel between the two transducers. The difference in the transit time measured is directly and exactly related to the velocity of the liquid in the pipe.
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.
Turbulent Flow	–	When forces due to inertia are more significant than forces due to viscosity. This typically occurs with a Reynolds number in excess of 4000.
Union	–	A form of pipe fitting where two extension pipes are joined at a separable coupling.
Vacuum	–	Any pressure less than atmospheric pressure.
V-cone	–	A constriction consisting of a cone suspended in the flow stream. It can be used in locations where little space for upstream and downstream piping is available.
Velocity	–	The time rate of change of displacement; dx/dt.
Velocity Flow Measurement	–	Velocity flow meters utilize techniques that measure the velocity of the flowing stream to determine the volumetric flow. Examples of flow meter technologies that measure velocity include magnetic, turbine, ultrasonic, and vortex shedding and fluidic flow meters.
Venturi Tube	–	A constriction consisting of a streamlined reduction and expansion of the piping containing an inlet section, throat, and outlet section.
Vibration Error	–	The maximum change in output of a transducer when a specific amplitude and range of frequencies are applied to a specific axis at room temperature.
Vibration Error Band	–	The error recorded in output of a transducer when subjected to a given set of amplitudes and frequencies.
Viscosity	–	The inherent resistance of a substance to flow. The viscosity of a fluid is the ability of the fluid to flow over itself. Water has a viscosity of about 1 cP.
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.
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 flow rate, V = average fluid velocity, and A = cross sectional area of the pipe.
Volumetric Flow Measurement	–	Volumetric flow meters directly measure the volume of fluid passing through the flow meter. The only flow meter technology that measures volume directly is the positive displacement flow meter.
Vortex Precession	–	Flow meters use inlet vanes to rotate the fluid to form a vortex center (similar to a cyclone) that rotates around the inside of the pipe. The rotation of the vortex can be related to the flow rate.
Vortex Shedding	–	These flow meters alternately generate vortices on both sides of a bluff body located in the flow stream. The number of vortices formed can be related to the flow rate.
Water	–	Water can exhibit different properties depending upon its impurities. Whereas water with many impurities can be very conductive, de-ionized water is a form of pure water that is not very conductive. Boiler feed water often softened or de-mineralized before it is fed into boilers.
Watt Density	–	The watts emanating from each square inch of heated surface area of a heater. Expressed in units of watts per square inch.
Working Standard	–	A standard of unit measurement calibrated from either a primary or secondary standard, which is used to calibrate other devices or make comparison measurements.
Zero Offset	–	1. The difference expressed in degrees between true zero and an indication given by a measuring instrument.