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

DSP
Digital signal processing or digital signal processor.

Dual Element Sensor
A sensor assembly with two independent sensing elements.

Drop
A connection between a terminal and a subscriber.

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.

Droop
A common occurrence in time-proportional controllers. It refers to the difference in temperature between the set point and where the system temperature actually stabilizes due to the time-proportioning action of the controller.

DRAM
Dynamic Random Access Memory.

Double Precision
The degree of accuracy that requires two computer words to represent a number. Numbers are stored with 17 digits of accuracy and printed with up to 16 digits.

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

DNS
Domain Name System. A mechanism used in the Internet for translating names of host computers into addresses. The DNS also allows host computers not directly on the Internet to have registered names in the same style.

Dithering
The technique of adding controlled amounts of noise to a signal to improve overall system loop control, or to smear quantizing error in an A/D convertor application.

DLL
Dynamic Linked Library.

Dissociation Constant (K)
A value which quantitatively expresses the extent to which a substance dissociates in solution. The smaller the value of K, the less dissociation of the species in solution. This value varies with temperature, ionic strength, and the nature of the solvent.

Dissipation Constant
The ratio for a thermistor which relates a change in internal power dissipation to a resultant change of body temperature.

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.

Discharge Time Constant
The time required for the output-voltage from a sensor or system to discharge 37% of its original value in response to a zero rise time step function input. This parameter determines a low frequency response.

DIN 43760
The standard that defines the characteristics of a 100 ohm platinum RTD having a resistance vs. temperature curve specified by a = 0.00385 ohms per degree.

DIN
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.

Digital Output
An output signal which represents the size of an input in the form of a series of discrete quantities.

Digital Filtering
The process of smoothing, or removing noise from a signal via mathematical functions that are performed on the digital data stream.

Digit
A measure of the display span of a panel meter. By convention, a full digit can assume any value from 0 through 9, a 1/2-digit will display a 1 and overload at 2, a 3/4-digit will display digits up to 3 and overload at 4, etc. For example, a meter with a display span of ±3999 counts is said to be a 3-3/4 digit meter.

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
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.

Diaphragm
The sensing membrane which is deformed when pressure is applied.

Dielectric Constant
Related to the force of attraction between two opposite charges separated by a distance in a uniform medium.

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

DFT
Discrete Fourier Transform.

Desorption
Release of adsorbed or absorbed material .

Derivative
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.

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

Degree
An incremental value in the temperature scale, i.e., there are 100° 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.

Default
The value(s) or option(s) that are assumed during operation when not specified.

Deflection
The change in length along the primary axis or distance a diaphragm moves at the center between no-load and rated load conditions.

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

Dead Volume
The volume inside the pressure port of a transducer at room temperature and barometric pressure.

Debug
To find and correct mistakes in a program.

Decibel
A unit (dB) for measuring the relative strength of signal power. The number of decibels equals ten times the logarithm (base 10) of the ration of the measured signal power to a reference power. One tenth of a bell.

Dead Band
1. For chart records: the minimum change of input signal required to cause a deflection in the pen position. 2. For temperature controllers: the temperature band where heat is turned off upon rising temperature and turned on upon falling temperature expressed in degrees. The area where no heating (or cooling) takes place.

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

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.

Data Compression
A method of reducing the number of bits that are needed to represent information. Data compression allows gigher communications speeds and allows more information to be stored on a disk.

Data Base
A large amount of data stored in a well-organized manner. A data base management system (DBMS) is a program that allows access to the information.

DARPA
Defense Advanced Research Projects Agency. A US Dept of Defense agency that funds high-risk research projects and that funded the development of UNIX 4.2, and the TCP/IP communications protocol. One of the founders of the Internet.

Damping
The reduction of response at the resonant frequency through the use of a damping media such as oil. Usually specified as the ratio of critical damping.

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

Curve Fitting
Curve fitting is the process of computing the coefficients of a function to approximate the values of a given data set within that function. The approximation is called a 'fit'. A mathematical function, such as a least squares regression, is used to judge the accuracy of the fit.

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.

Cure Point
The temperature at which a normally magnetic material goes through a magnetic transformation and becomes non-magnetic.

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

CSA
Canadian Standards Administration.

Crosstalk
The unwanted transfer of energy from one communications circuit to another.

Cryogenics
Measurement of temperature at extremely low values, i.e., below -200°C.

Critical Speed
The rotational speed of the rotor or rotating element at which resonance occurs in the system. The shaft speed at which at least one of the 'critical' or natural frequencies of a shaft is excited.

CPU
Central processing unit. The part of the computer that contains the circuits that control and perform the execution of computer instructions.

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.

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.

Counter Weight
A weight added to a body so as to reduce a calculated unbalance at a desired place.

Coriolis Force
A result of centripetal force on a mass moving with a velocity radially outward in a rotating plane.

Coulomb
A measurement of the quantity of electrical charge, usually expressed as pico coulomb (10-12 coulombs).

Conversion Factors & Tables
This is an ongoing student project at Univ of Wisc. Quite complete and can be downloaded.

Control Point
The temperature at which a system is to be maintained.

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.

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

Control Character
A character whose occurrence in a particular context starts, modifies or stops an operation that effects the recording, processing, transmission or interpretation of data.

Constantan
A copper-nickel alloy used as the negative lead in Type E, Type J, and Type T thermocouples.

Contention
A method of line control in which terminals compete with each other for permission to transmit over a common channel. If the channel is free, the terminal transmits. If the channel is in use by another terminal, the terminal attempting to transmit waits until the channel is free.

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.

Conformity Error
For thermocouples and RTDs, the difference between the actual reading and the temperature shown in published tables for a specific voltage input.

Confidence Level
The range (with a specified value of uncertainty, usually expressed in percent) within which the true value of a measured quantity exists.

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

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

Compression Ration
The ratio of the number of bits required to represent the original information to the number of bits required to represent the compressed signal.

Compiler
A program that translates a high-level language, such as Basic, into machine language.

Complex Function
Any mathematically defined relationship given by the following expression

Compensating Alloys
Alloys used to connect thermocouples to instrumentation. These alloys are selected to have similar thermal electric properties as the thermocouple alloys (however, only over a very limited temperature range).

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

Communications Port
A connection on a terminal through which data is input and/or output.

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.

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.

Coherence Function.
A frequency domain function computed to show the degree of a linear, noise-free relationship between a system's input and output. The value of the coherence function ranges between zero and one, where a value of zero indicates there is no causal relationship between the input and the output. A value of one indicates the existence of linear noise-fr…

Coaxial Cable
A tubular wire transmission medium that consists of a central conductor surrounded by a dielectric insulator tht is in turn surrounded by a tubular conductor. The outer conductor is usually at ground potential and also serves as an electrical shield.

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).

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).

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.

Clock
The device that generates periodic signals for synchronization.

Clipping
The term applied to the phenomenon which occurs when an output signal is limited in some way by the full range of an amplifier, ADC or other device. When this occurs, the signal is flattened at the peak values, the signal approaches the shape of a square wave, and high frequency components are introduced. Clipping may be hard, as is the case when t…

Client-Server Network
A network that uses a central computer (server) to store data that is accessed from other computers on the network (clients).

Clear
To restore a device to a prescribed initial state, usually the zero state.

CHROMEGA®
A chromium-nickel alloy which makes up the positive leg of type K and type E thermocouples (registered trademarks of OMEGA ENGINEERING, INC.).

Circuit Switching
A method of establishing a dedicated communications path between two or more locations through one or more switching nodes. Data is sent in a continuous stream; the data rate is constant; the delay is constant and limited to propagation times; and a dedicated end to end path remains in effect until the communication is terminated.

Checksum
A block check character that is formed by taking the sum of the binary data transmitted.

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

Charge Sensitivity
For accelerometers that are rated in terms of charge sensitivity, the output voltage (V)is proportional to the charge (Q) divided by the shunt capacitance (C). This type of accelerometer is characterized by a high output impedance. The sensitivity is given in terms of charge; picocoulombs per unit of acceleration (g).

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

Character
A letter, digit or other symbol that is used as the representation of data. A connected sequence of characters is called a character string.

Ceramic Insulation
High-temperature compositions of metal oxides used to insulate a pair of thermocouple wires The most common are Alumina (Al2O3), Beryllia (BeO), and Magnesia (MgO). Their application depends upon temperature and type of thermocouple. High-purity alumina is required for platinum alloy thermocouples. Ceramic insulators are available as single and mul…

Ceramic
Polycrystalline ferroelectric materials which are used as the sensing units in piezoelectric accelerometers. There are many different grades, all of which can be made in various configurations to satisfy different design requirements.

Centripetal Force
A force exerted on an object moving in a circular path which is exerted inward toward the center of rotation.

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

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.