Glossary

Conversion Tables

Hazardous Location Classification

Pressure Transducer Installation and Use

Waterhammer

GLOSSARY

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

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

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).

Peltier Effect: When a current flows through a thermocouple junction, heat will either be absorbed or evolved depending on the direction of current flow. This effect is independent of joule I2 R heating.

Perfectly Balanced Rotor: A rotor is perfectly balanced when its mass distribution is such that it transmits no vibratory force or motion to its bearings as a result of centrifugal forces.

Peripheral: A device that is external to the CPU and main memory, i.e., printer, modem or terminal, but is connected by the appropriate electrical connections.

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).

pH(S) (Standard pH Scale): The conventional standard pH scale established on the basis that an individual ionic activity coefficient can be calculated from the Debye-H¸ckel law for primary buffers.

Phase Difference: The time expressed in degrees between the same reference point on two periodic waveforms.

Phase Proportioning: A form of temperature control where the power supplied to the process is controlled by limiting the phase angle of the line voltage.

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.

PID: Proportional, integral, derivative. A three mode control action where the controller has time proportioning, integral (auto reset) and derivative rate action.

Piezoelectric Accelerometer: A transducer that produces an electrical charge in direct proportion to the vibratory acceleration.

Piezoresistance: Resistance that changes with stress.

Pixel: Picture element. Definable locations on a display screen that are used to form images on the screen. For graphic displays, screens with more pixels provide higher resolution.

Plane Separation: Of a balancing machine, is the operation of reducing the correction plane interference ratio for a particular rotor.

Platinel: A non-standard, high temperature platinum thermocouple alloy whose thermoelectric voltage nearly matches a Type K thermocouple (Trademark of Englehard Industries).

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.

Poisson Ratio: The ratio between the strain of expansion in the direction of force and the strain of contraction perpendicular to that force v = -Et/E1.

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

Polarization: The inability of an electrode to reproduce a reading after a small electrical current has been passed through the membrane. Glass pH electrodes are especially prone to polarization errors caused by small currents flowing from the pH meter input circuit and from static electrical charges built up as the electrodes are removed from the sample solution, or when the electrodes are wiped.

Port: A signal input (access) or output point on a computer.

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.

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

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 Device: Part of a flowmeter which is mounted internally or externally to the fluid conduit and produces a signal corresponding to the flowrate and from which the flow may be determined.

Primary Standard (NBS): The standard reference units and physical constants maintained by the National Bureau of Standards upon which all measurement units in the United States are based.

Primary Standards: Aqueous pH buffer solutions established by the National Bureau of Standards within the 2.5 to 11.5 pH range of ionic strength less than 0.1 and which provide stable liquid junction potential and uniformity of electrode sensitivity.

Principal Axes: The axes of maximum and minimum normal stress.

Probe: A generic term that is used to describe many types of temperature sensors.

Process Meter: A panel meter with sizeable 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.

Program: A list of instructions that a computer follows to perform a task.

Prom: Programmable read-only memory. A semiconductor memory whose contents cannot be changed by the computer after it has been programmed.

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.

Proportioning Band: A temperature band expressed in degrees within which a temperature controller's time proportioning function is active.

Proportioning Control Mode: A time proportioning controller where the amount of time that the relay is energized is dependent upon the system's temperature.

Proportioning Control plus Derivative Function: A time proportioning controller with a derivative function. The derivative function senses the rate at which a system's temperature is either increasing or decreasing and adjusts the cycle time of the controller to minimize overshoot or undershoot.

Proportioning Control plus Integral: A two-mode controller with time proportioning and integral (auto reset) action. The integral function automatically adjusts the temperature at which a system has stabilized back to the setpoint temperature, thereby eliminating droop in the system.

Proportioning Control with Integral and Derivative Functions: Three mode PID controller. A time proportioning controller with integral and derivative functions. The integral function automatically adjusts the system temperature to the set point temperature to eliminate droop due to the time proportioning function. The derivative function senses the rate of rise or fall of the system temperature and automatically adjusts the cycle time of the controller to minimize overshoot or undershoot.

Protection Head: An enclosure usually made out of metal at the end of a heater or probe where connections are made.

Protection Tube: A metal or ceramic tube, closed at one end into which a temperature sensor is inserted. The tube protects the sensor from the medium into which it is inserted.

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.

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

Radiation: See Infrared

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.

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.

Rate Action: The derivative function of a temperature controller.

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

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.

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

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

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.

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.

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.

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

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 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.

Reserved Word: A word that has a defined function in the language, and cannot be used as a variable name.

Residual (Final) Unbalance: Residual unbalance is that unbalance of any kind that remains after balancing.

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).

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

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.

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.

RFI: Radio frequency interference.

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 closely to those of the final supporting system.

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.

Rotor: A rotor is a rotating body whose journals are supported by bearings.

RTD: Resistance temperature detector.

Salt Bridge: The salt bridge of a reference electrode is that part of the electrode which contains the filling solution to establish the electrolytic connection between reference internal cell and the test solution. Auxiliary Salt Bridge: A glass tube open at one end to receive intermediate electrolyte filling solution, and the reference electrode tip and a junction at the other end to make contact with the sample.

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

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

SCE: Saturated calomel electrode.

SCR: Ssilicone controlled rectifier.

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

Secondary Device: A part of the flowmeter which receives a signal proportional to the flowrate, from the primary device, and displays, records and/or transmits the signal.

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.

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

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 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.

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

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.

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

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.

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.

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.

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-Plane (Static) Balancing Machine: A single plane balancing machine is a gravitational or centrifugal balancing machine that provides information for accomplishing single plane balancing.

Slope (Electrode Sensitivity, Span): See Nernst factor.

Smallest Bending Radius: The smallest radius that a strain gage can withstand in one direction, without special treatment, without suffering visible damage.

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

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.

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.

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

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

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

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°.

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.

Spot Size: The diameter of the circle formed by the cross section of the field of view of an optical instrument at a given distance.

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.

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.

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. It can be sensed in a small hole drilled perpendicular to and flush with the flow boundaries so as not to disturb the fluid in any way.

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

Steady Flow: A flow rate in the measuring section of a flow line that does not vary significantly with time.

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.

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

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.

String: A sequence of characters.

Strouhal Number: A nondimensional parameter important in vortex meter design defined as: s = Fh/V where f = frequency, V = velocity, and h = a reference length

Super Cooling: The cooling of a liquid below its freezing temperature without the formation of the solid phase.

Super Heating: 1. The heating of a liquid above its boiling temperature without the formation of the gaseous phase. 2. The heating of the gaseous phase considerably above the boiling-point temperature to improve the thermodynamic efficiency of a system.

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.

Suspension Effect: The source of error due to varied reference liquid junction potential depending upon whether the electrodes are immersed in the supernatant fluid or deeper in the sediment. Normally encountered with solutions containing resins or charged colloids.

Syntax: The rules governing the structure of a language.