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Technical Glossary

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A
  • Absolute Pressure
    The pressure measured using an ideal vacuum as a zero reference point.
  • Accuracy: The degree of precision. Usually expressed, in terms of error, as a percentage of the specified value, or as a percentage of a range. The combined error due to nonlinearity, no repeatability, and hysteresis expressed as a percentage of full scale output.
  • A/D: Analog-to-digital conversion. The process changes an analog signal into a digital value representative of the magnitude of the signal at the moment of conversion.
  • Absolute pressure (psia): The total force per unit area exerted by a fluid. It is the sum of atmospheric and gauge pressures.
  • Alternating current (AC): Current which reverses polarity at a uniform frequency.
  • Atmospheric pressure: The force exerted on a unit area by the weight of the atmosphere.
  • Adaptive-Tune
    Dynisco's continuous self-tuning algorithm based on the dominant poles theory. Available only in the Automatic mode of operation.
  • Adaptive Tuning
    A self-tuning function that continuously monitors the dynamics of a process and makes adjustments to the control parameters to maintain a pre-determined setpoint.
  • Agency Approval
    Certification of conformity to the requirements of various independent testing agencies such as Underwriters Laboratories or the Canadian Standards Association.
  • Alarm
    A point in a process if the value increases above (high alarm) or decreases below (low alarm), causes an action by an indicator or controller.
  • Ambient Conditions
    The condition(s) around the transducer (pressure, temperature, etc).
  • Ambient Pressure
    The pressure of the medium surrounding the transducer.
  • Ambient Temperature
    The average or mean temperature of the surrounding air which comes in contact with the equipment and instrument under test.
  • Amplifier
    An electronic device which boots or increases a small signal to a higher level, usually for transmission, scale convenience, or noise immunity.
  • Analog Output
    A voltage or current signal that is a continuous function of the measured parameter.
  • ANSI
    American National Standards Institute.
  • Auto/Manual Station
    The controller function that allows the operator to select the Automatic or Manual control mode. In the automatic control algorithm the controller determines the control output. In the Manual mode, the operator determines the control output.
B
  • Background Noise
    The total noise from all sources of interference in a measurement system independent of the presence of a data signal.
  • Baud rate: A unit of measure for data transmission speed. It represents the number of signal elements (typically bits) transmitted per second. Typical baud rates are 300, 1200, 2400, 4800, 9600, 14400, and 28800.
  • Buffer: In chemistry terms, a solution that maintains a set pH value regardless of added acids or bases; often used for calibration.

In computer terms, a device used to store data temporarily, normally to compensate for differences in speed between system components (for example, a high-speed data acquisition board and main memory).

  • Byte: Eight related bits of information processed as a unit. Eight bits equal one byte.
  • Boiling Point
    The temperature at which a substance in the liquid state transforms to the gaseous state (commonly refers to the boiling point of water (100°C (212°F) at sea level).
  • Breakdown Voltage Rating
    The AC or DC voltage, which can be applied across the insulation portion of a transducer without arcing or conduction above a specific current value.
  • BTU: British Thermal Unit
    The quantity of thermal energy required to rise one pound of water 1°F at or near its maximum density (39.1°F) (1055J).
  • Burst Pressure
    The maximum pressure applied to a transducer sensing element or case without causing leakage.
C
  • Calibration
    (1)A test during which known values of pressure are applied to the transducer and corresponding output readings are recorded under specified conditions.
    (2)The matching of a pressure controller or indicator to the characteristics of a specific transducer. Most frequently done utilizing span resistor internal to the pressure transducer. Procedure is termed RCal.
    (3)Adjustment of an instrument to standards of known accuracy and stability.
  • Calibration Cycle
    Pressure calibration in both a descending and ascending mode.
  • Compensation
    The addition of specific material or device(s) to counteract a known error.
  • Configuration
    Selection from menus, and switches or jumpers, those options on an instrument to be used in a specific process.
  • Controlled Variable
    A process variable which is to be controlled at some desired value by means of error; i.e. cold junction compensation for thermocouples.
  • Controller
    A device which manipulates one process variable (RPM, Heat, etc.) to result in a stable condition of a second (controlled) variable (pressure, temperature, etc).
  • Control Output
    The output signal from a controller to the manipulated variable in response to input signals from the controlled variable. (See direct acting; reverse acting).
  • Current Loop
    A two-wire loop in which the current through the wires is maintained according to a controlling device, usually a two-wire transmitter. The advantages of a current loop are longer distance signal transmission, better noise immunity, and the ability to power the two-wire transmitter throughout the same two wires. The most common current loop is 4 to 20 mA.
  • Cycle Time
    The time usually expressed in seconds for a controller to complete one on/off cycle.
  • Cavitation: Process in which small bubbles are formed and implode violently. This results in aggressive cleaning action in ultrasonic cleaners.
  • Contacts: Elements used to mechanically make or break an electric circuit.
  • Continuous duty: A device able to operate continuously with no off or rest periods.
  • Convection: Transmission of energy or mass in a medium by movement of the medium itself.
D
  • DC
    Direct Current.
  • Dead Band
    The range through which input can be varied without initiating observable change in output. (There is a separate and distinct input-output relationship for increasing and decreasing signals.)
  • Dead Volume
    The volume of the pressure port of a transducer at room temperature and ambient barometric pressure.
  • Derivative PID Parameter (also called rate)
    Reacts to the rate of rise, fall or recovery of a process.
  • Deviation
    The difference between the value of the controlled variable and the value at which it is being controlled.
  • Differential Pressure
    The static pressure difference generated by the primary device when there is no difference in elevation between the upstream and downstream pressure taps.
  • Digital Input
    Auxiliary input to an indicator or controller which performs a function via switch closure or opening. Typically used to reset a latched alarm, or to duplicate a front panel function such as selection of automatic or manual control modes.
  • Digital Output
    An output signal, which represents the size of a stimulus or input in the form of a series of discrete quantities.
  • Direct Acting
    Control output action which increases as the process variable increases. In the case of an alarm, a direct acting alarm has its relay activated in an alarm condition.
  • Disturbance
    An undesired change that takes place in a process(es) that tends to affect adversely the value of a controlled variable.
  • Drift
    An undesired change in output over a period of time, of which change is not a function of the measurand
  • Density: The mass of a given substance per unit volume, often expressed as pounds/ft3 or grams/cm3.
  • Direct current (DC): A current with a constant polarity.
  • Double-pole, double-throw (DPDT): A term used to describe a switch or relay output contact form (form C). Two separate switches that operate simultaneously, each with a normally open and normally closed contact and a common connection.
E
  • End Point
    The output at zero pressure and full-scale pressure.
  • Environmental Conditions
    All conditions to 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 pressure being sensed.
  • Error Band
    The allowable deviation of output from specific reference norm.
  • Excitation
    The voltage supplied by an indicator or controller to a transducer to provide its proper operating conditions.
  • Explosion-proof (XPRF) motor: A totally enclosed motor that will withstand an explosion of a specific vapor or gas within its housing, or will prevent sparks or flashes generated within its housing from igniting surrounding vapor or gas.
F
  • Fahrenheit
    A temperature scale defined by 32° at the ice point and 212° at the boiling point of water at sea level.
  • Fail-Safe
    See Reverse Acting.
  • Filter (Electrical)
    A device to sort desired result from undesired. Electrically, a selective circuit which passes through certain frequencies, while attenuating or rejecting others.
  • FM-Approved
    An instrument that meets a specific set of specifications established by the Factory Mutual Research Corporation which sets industrial safety standards.
  • Freezing Point
    The temperature at which the substance goes from a liquid phase to a solid phase.
  • Full Bridge
    A Wheatstone Bridge configuration utilizing active elements or stain gauges.
  • Full Scale Output
    The electrical output of the pressure device with full scale pressure applied. Usually expressed in electrical units (mV/V, V, mA)
  • Full Scale Pressure
    The maximum pressure under which applicable performance specifications apply.
  • Factory calibration: The tuning or altering of a control device by the manufacturer to bring it into specification.
G
  • Gauge Pressure
    The difference between the local absolute pressure of the fluid and the atmospheric pressure at the place of the measurement. (OR)
  • Gauge pressure (psig): A measure of the force per area exerted by a fluid using atmospheric pressure as a zero reference.
  • Gain
    The ratio of the change in output to the change in input, which caused it.
  • Gain Adjustment
    Means of adjusting the full scale output of an amplified transducer.
  • Ground
    The reference point of an electrical system, or alternatively, the local earth potential (earth ground).
H
  • Half Bridge
    2 active elements or stain gauges.
  • HART Digital Communication
    HART (Highway Addressable Remote Transducer), was originally developed by Rosemount and is now owned by the HART Communication Foundation (HCF). HART provides a standard twisted pair of wires with a 4-20 mA signal and digital capabilities for up to 15 additional signals (analog and digital) over the same twisted pair with two-way communication.
  • Heat
    Thermal energy. Heat is expressed in units of calories or Btu's.
  • Hysteresis
    Deviation in output within the transducer range when first approaching this point with increasing pressure and then with decreasing pressure.
I
  • Indicator
    A device which monitors and displays the condition of a process variable without exerting any control action. Indicators may be equipped with alarms or other auxiliary outputs.
  • Input and Output Resistance
    The resistance measured across the input (excitation) and output (signal) terminals of an unamplified transducer.
  • Input Fail Safe
    Direction in which signal is driven in the event of a sensor failure. Upscale will drive the signal fully upscale, and downscale will drive the signal fully downscale. The control output will respond as if the sensor has not failed.
  • Insulation Resistance
    The resistance measured between specified insulated portions of a transducer when a specific DC voltage is applied at room conditions.
  • Integral
    PID parameter (also called reset) which monitors and corrects the error signal between the setpoint and the process variable.
  • Intrinsically Safe
    An instrument which will not produce any spark or thermal effect, under normal or abnormal conditions, that will ignite a specified gas mixture.
  • Impedance: The opposition in an electric circuit to the flow of an alternating current. It consists of ohmic resistance, inductive reactance, and capacitive reactance.
  • Inductive load: Electrical devices made of wound or coiled wire. Current passing through the coil creates a magnetic field that in turn produces mechanical work.
J
  • Jumpers
    Wire links that allow for changes to be made in input and output hardware configurations.
K
  • Kelvin
    (Symbol K) The units 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 = 273.16K (there is no degree [°] symbol used with the Kelvin scale).
L
  • Linearity (or nonlinearity)
    The maximum deviation of the transducer output from a defined straight line during increasing pressure in a calibration cycle.
  • Linearity (End Point/or Terminal)
    Linearity as referring to a straight line between end points.
  • Loop Gain
    The product of the gains of all the elements in a loop.
  • Loop or Transmitter Power Supply
    24 Volt DC (nominal) supplied by an indicator or controller power 2 or 4 wire transmitters.
  • LIMS (Laboratory Information Management System): A system that manages operations of a testing laboratory.
  • Linearity: The degree to which performance or response approaches the condition of being linear. Expressed in percent.
M
  • Maximum Diaphragm Temperature
    The maximum temperature of the process media to which the transducer tip below the mounting threads can be exposed. Maximum strain gage temperature is the maximum environmental temperature at which the strain gage housing should be exposed.
  • Maximum Pressure
    Pressure that may be applied to a transducer without changing the transducers' performance beyond specified tolerances.
  • Measurand
    A physical quantity, property or condition which is measured. The term measurand is preferred to "input", "parameter to be measured", "physical phenomenon", "stimulus", and/or "variable."
  • Melting Point
    The temperature at which a substance transforms from a solid phase to a liquid phase.
  • Melt Pressure Transducer
    A device specifically designed to measure the pressure of molten polymers. This device produces an electrical signal proportional to the pressure of the molten polymers.
  • Mounting Error
    The error resultant from installing the pressure transducer, both electrical and mechanical.
N
  • NEMA-4
    A standard from the National Electrical Manufacturers Association, which defines enclosures for indoor or outdoor use primarily to provide a degree of protection against windblown dust, rain, and/or splashing water.
  • Noise
    An unwanted signal which can contribute to errors in measurement. Examples are hum (power lines), radio frequency interference (RFI), electromagnetic interference (EMI), and broadband or white noise.
  • Normally Open
    The state of a switching device (relay or SSR) whose non-powered state provides no connection. OR A switch in which the contacts are open (separated) when no external forces act upon the switch.
  • Normally Closed
    The state of a switching device (relay or SSR) whose non-powered state is connected.OR A switch in which the contacts are closed (contacting) without any external force acting upon it.
O
  • Output
    The electrical signal, which is produced by a pressure applied to the transducer sensor.
  • On/off control: A simple control system in which the device being controlled is either full on or full off, with no intermediate operating positions.
  • Open drip-proof (ODP) motor: An open motor with ventilator openings that will prevent liquids and solids, dropped from an angle of 0° to 15° from vertical, from interfering with its operation.
P
  • PID
    The control algorithm providing proportional control with automatic Integral and Derivative terms. Mathematically determines the control action to be performed.
  • Polarity
    In electricity, the quality of having two oppositely charged poles, one positive and one negative.
  • Positive Feedback
    A closed loop in which any change is reinforced until a limit is eventually reached.
  • Potentiometer
    A variable resistor often used to control a circuit.
  • Power Supply
    A separate unit or part of a circuit that supplies power to the rest of the circuit or to a system.
  • Pressure Range
    The pressure values over which a transducer is intended to measure, specified by their upper and lower limits.
  • Primary Loop
    The outer loop in a cascade system.
  • Proof Pressure
    The maximum amount of pressure that can be applied to a pressure transducer without changing any specification. See maximum pressure.
  • Proportional Band
    The PID parameter which determines the area in which the proportional control algorithm is operative.
  • Proportional Control
    (1)Current or Voltage: Control algorithm which determines a continuous linear relationship between the input and the output.
    (2) Time proportioning: Control algorithm that determines the time that a control output remains in the "ON" condition in a finite cycle. In this case, when the output is "ON", it is fully on.
  • PSIA
    Pounds per square inch absolute. Pressure referenced to a vacuum.
  • PSIG
    Pounds per square inch gage. Pressure referenced to ambient air pressure.
  • PV-Process Variable
    This is the controlled variable in a control situation or the monitored variable in an indicated situation.
  • Parallel transmission: The transmission of data bits over different lines, usually simultaneously; as opposed to serial transmission.
  • pH: An indication of the acidity or alkalinity of a solution. Units range from 0 (most acidic), to 7 (neutral), to 14 (most alkaline).
  • PID control (proportional, integral, derivative): Control in which the control signal is a linear combination of the error signal, its integral, and its derivative.
  • Pressure: Force exerted per unit area.
  • Proportional control: Control in which the amount of corrective action is proportional to the amount of error.
R
  • Range
    The upper and lower pressure limits that a transducer is required to measure.
  • Repeatability
    The ability of a transducer to reproduce output readings when the same pressure value is applied to it consecutively, under the same conditions, and in the same direction.
  • Rate Time
    The time interval over which the system variable is sampled for the derivative function.
  • 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.
  • Remote Setpoint
    An analog input to a controller which allows the setpoint to be changed by a remote device. This can be another instrument (cascading), a PLC, a computer or it can be done manually.
  • Retransmission Output
    An analog output from an indicator or controller directly proportional to the value of the PV. Also called the recorder output.
  • Reverse Acting
    Control output that decreases as the process variable increases. In the case of an alarm, a reverse acting alarm has its relay activated in the non-alarm state. This is also called a fail-safe alarm.
  • RFI
    Radio Frequency Interference.
  • Room Condition
    Ambient conditions used for test purposes.
S
  • Safe Overpressure
    The maximum pressure that can be applied to a transducer without changing its performance beyond specified tolerances.
  • Self-Heating
    Internal heating of a transducer as a result of power dissipation.
  • Self-Regulation
    The property of a process or machine which permits attainment of equilibrium, after a disturbance, without the intervention of a controller.
  • Self-Tuning
    Generic term for algorithms from a number of manufacturers which more or less succeed in tuning the PID parameters of controllers and control systems automatically. The term is non-specific, and individual manufacturers should be consulted regarding their algorithms.
  • Sensing Element
    The part of a transducer, which reacts directly in response to the pressure.
  • Sensitivity
    The ratio of the change in transducer output to a change in the value of the pressure.
  • Sensitivity Shift
    A change in the calibration slope.
  • Setpoint
    An input variable which sets the desired value of a controlled variable.
  • Shield
    A protective enclosure surrounding a circuit or cable which is to protect it from an electrical disturbance such as noise.
  • Shunt Calibration/Rcal
    A method of generating an electrical output to match the electrical output that would be given in response to an applied pressure. This is accomplished using a resistor to unbalance the bridge electrically rather than with strain introduced by applied pressure. With standardized shunt or Rcal, the same point (generally 80%) is chosen on the calibration curve so that all similar transducers calibrate at the same point to facilitate interchangeability.
  • Signal Conditioner
    An electronic network that permits adjustments to match a particular transducer to a readout device. Generally included are provisions for adjusting for zero balance and span or sensitivity.
  • 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, digitizing, and linearizing.
  • SMART
    Dynisco's name for its proprietary two part self-tuning algorithm. It consists of TUNE and ADAPTIVE-TUNE.
  • Span
    The algebraic difference between the limits of the range.
  • Span Turndown
    The ability to re-range a transmitter to lower ranges. The re-ranging allows the 20 mA signal to be adjusted to the lower range which provides improved resolution.
  • Stability
    The ability of a transducer to retain its performance characteristics for a period of time and under a variety of conditions.
  • Strain Gauge
    A measuring element for converting force, pressure, tension, etc., into an electrical signal.
  • Static Calibration
    A calibration recording pressure versus output at room temperature.
  • Static Error Band
    The error band applicable at room temperature.
  • Static Pressure
    The pressure of a fluid or gas at rest.
  • Serial transmission: Sending one bit at a time on a single transmission line.
  • Series (Universal) motor: A non-induction type motor utilized for small equipment. Speed will decrease as load increases.
  • Shaded-pole motor: A low-starting-torque motor that depends on induced current to create the magnetic field necessary to start the motor.
  • Shunt: A conductor joining two points in an electrical circuit to form a parallel path. All or some portion of the current may pass through the shunt.
  • Single-phase motor: Any motor energized by a single alternation voltage.
  • Single-pole, double-throw (SPDT) switch: A switch that in one position completes one of two circuits. In the second position the switch completes a second circuit and breaking the first circuit.
  • Single-pole, single-throw (SPST) switch: A switch that will open or complete a circuit.
  • Solid-state: Any element that controls current without moving parts, heated filaments, or vacuum gaps.
  • Standard operating conditions, standard temperature and pressure (STP): Defined temperature and pressure to which all values are referenced for comparison. Generally 760 mm Hg (1 atm), 25°C.
  • Stop bit: A signal following a character or block that prepares the receiving device to receive the next character or block.
T
  • Temperature Effect on Span
    The percentage change in rated output per degree change in ambient temperature.
  • Temperature Effect on Zero
    The percentage change in zero balance due to a change in ambient temperature.
  • Temperature Range, Operable
    The range of ambient temperature, given by their extremes, within which the transducer is intended to operate.
  • Temperature Range, Compensated
    The range of ambient temperature for which Thermal Zero Shift is applicable (temperature error). Operation outside this range may require re-calibration.
  • Temperature Range, Storage
    The range of ambient temperatures, given by their extremes, at which a transducer may be stored or transported.
  • Thermal Effect on Sensitivity
    The change in transducer full scale output due to the effects of temperature only.
  • Thermal Effect on Zero
    The change in transducer zero pressure output due to the effects of temperature only.
  • Thermal Sensitivity Shift
    The sensitivity shift due to changes of the ambient temperature from room temperature to the specified limits of the compensated temperature range.
  • Thermal Zero Shift
    An error due to changes in ambient temperature in which the zero pressure output shifts. Thus, the entire calibration curve moves in parallel displacement.
  • Transducer
    In the broadest sense it is a device (or medium) that converts one energy form to another. Therefore, items such as a windmill, electric light, or an automobile engine could be called a "transducer" - but, in common practice, the term is generally applied to devices that take a physical phenomenon (pressure, temperature, humidity, flow, etc.) and converts it to an electrical output.
  • Transmitter
    A device which translates the low-level output of a sensor or transducer to a higher level signal which is suitable for transmission to a site where it can be processed further.
  • TUNE
    Dynisco's one-shot algorithm that determines PID parameters based on a step change in output in the manual mode of operation.
  • Temperature compensation: Correction for the influence of temperature on a measurement.
  • Tolerance: The maximum allowable deviation from a specified standard, as the range of variation permitted, expressed in actual values or more often as a percentage of the nominal value.
  • Totally enclosed (TE) motor: Motors that prevent the free flow of air from the inside of the motor enclosure to the outside.
  • Totally enclosed, nonventilated (TENV) motor: A motor in a totally enclosed housing that is not equipped with an external cooling device.
  • Totally enclosed, fan-cooled (TEFC) motor: A motor in a totally enclosed housing that is equipped with a separate external blower.
  • Three-phase motor: A relatively inexpensive, self-starting motor (no starting winding or capacitor); can start heavy loads. The motor requires a three-phase AC power supply.
V
  • Viscosity: The resistance of a fluid to flow when subjected to shear stress.
Y
  • Y2K
    Potential for a computer or time/date stamped instrumentation to cease functioning at midnight on January 1, 2000. None of Dynisco's present or past instrumentation is subject to the Y2K problem.
Z
  • Zero Adjustment
    Means of adjusting the zero pressure output of an amplified transducer.
  • Zero Balance (offset)
    The measured transducer output under room conditions with no pressure applied to the pressure port. For absolute pressure transducers, this value is measured at 0 psia. Gage and sealed pressure transducers have this value measured at atmospheric pressure.
  • Zero Shift
    Any parallel shift of the input/output curve.