Series D8 User’s Guide Glossary

Glossary

A

AC

See Alternating Current.

AC Line Frequency

The frequency of the ac line power measured in Hertz

(Hz), usually 50 or 60 Hz.

Accuracy

Closeness between the value indicated by a measuring instrument and a physical constant or kno wn standards.

Action

The response of an output when the process v ariable is changed. See also Direct Action, Reverse Action.

Address

A numerical identifier for a controller when used i computer communications.

Alarm

A signal that indicates that the process has e xceeded or fallen below a certain range around the set point.

For example, an alarm may indicate that a process is too hot or too cold. See also Failed Sensor Alarm,

Global Alarm, High De viation Alarm, High Alarm,

Loop Alarm, Low Deviation Alarm, Low Alarm.

Alarm Delay

The lag time before an alarm is activated.

Alternating Current (AC)

An electric current that re verses at re gular intervals, and alternates positive and negative values.

Ambient Temperature

The temperature of the air or other medium that sur rounds the components of a thermal system.

American Wire Gauge (AWG)

A standard of the dimensional characteristics of wire used to conduct electrical current or signals. AWG is identical to the Brown and Sharpe (B&S) wire gauge.

Ammeter

An instrument that measures the magnitude of an electric current.

Ampere (Amp, A)

A unit that defines the rate of f w of electricity (current) in the circuit. Units are one coulomb (6.25 x

1018 electrons) per second.

Analog Output

A continuously v ariable signal that is used to represent a v alue, such as the process v alue or set point value. Typical hardw are configurations are 0 t

20mA, 4 to 20mA or 0 to 5 Vdc.

Automatic Mode

A feature in which the controller sets PID control outputs in response to the process v ariable and the set point.

Automatic Reset

The integral function of a PI or PID temperature controller that adjusts the process temperature to the set point after the system stabilizes. The inverse of integral.

Autotune

A feature that automatically sets temperature control

PID values to match a particular thermal system.

AWG

See American Wire Gauge.

B

Baud Rate

The rate of information transfer in serial communications, measured in bits per second.

BCD

Binary coded decimal. F or BCD job loading, the binary states of three digital inputs are decoded as decimal numbers 1 to 8.

Bumpless Transfer

A smooth transition from automatic (closed loop) to manual (open loop) operation. The control output does not change during the transfer.

C

Calibration

The comparison of a measuring de vice (an unknown) against an equal or better standard.

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Celsius

A temperature scale in which w ater freezes at 0° C and boils at 100° C at standard atmospheric pressure.

The formula for conversion to the F ahrenheit scale is

°F = (1.8 x °C) + 32. Formerly known as Centigrade.

Central Processing Unit (CPU)

The unit of a computing system that includes the cir cuits controlling the interpretation of instructions and their execution.

Circuit

Any closed path for electrical current. A configuratio of electrically or electromagnetically-connected components or devices.

Class

The model for a software object. Objects of a class are similar to one another. DeviceNet classes define wha attributes and services objects of that type have. Class services are used to e xamine and change class attributes.

Closed Loop

A control system that uses a sensor to measure a process variable and makes decisions based on that feedback.

Cold Junction

Connection point between thermocouple metals and the electronic instrument.

Common Mode Rejection Ratio

The ability of an instrument to reject electrical noise, with relation to ground, from a common voltage. Usually expressed in decibels (dB).

Communications

The use of digital computer messages to link components. See also Serial Communications, Baud Rate.

Control Action

The response of the PID control output relati ve to the difference between the process v ariable and the set point. See also Direct Action, Reverse Action.

Current

The rate of fl w of electricity. The unit of measure is the Ampere (A). 1 Ampere = 1 coulomb per second.

Cycle Time

The time required for a controller to complete one onoff-on cycle. It is usually expressed in seconds.

Cyclic Redundancy Check (CRC)

An error checking method in communications that provides a high level of data security.

D

DAC

See Digital-to-Analog Converter.

Data Logging

A method of recording a process v ariable o ver a period of time. Used to review process performance.

DC

See Direct Current.

Default Parameters

The programmed instructions that are permanently stored in the microprocessor software.

Derivative Control (D)

The last term in the PID algorithm. Action that anticipates the rate of change of the process and compensates to minimize o vershoot and undershoot.

Derivative control is an instantaneous change of the control output in the same direction as the propor tional error. This is caused by a change in the process variable that decreases over the time of the derivative.

The derivative is expressed in seconds.

Deutsche Industrial Norms (DIN)

A set of technical, scientific and dimensional stan dards de veloped in German y. Man y DIN standards have worldwide recognition.

Deviation Alarm

See High Deviation Alarm, Low Deviation Alarm.

DeviceNet

DeviceNet is a netw ork that connects industrial devices. De viceNet is designed to pro vide a costeffective and rob ust solution to de vice netw orking.

DeviceNet is designed to transport control-oriented information associated with lo w-level de vices and other information related to the system being controlled, such as configuration parameters

Digital-to-Analog Converter (DAC)

A device that con verts a numerical input signal to a signal that is proportional to the input in some way.

DIN

See Deutsche Industrial Norms.

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Direct Action

An output control action in which an increase in the process variable causes an increase in the output. Usually used with cooling applications.

Direct Current (DC)

An electric current that fl ws in one direction.

Distributed Zero Crossing (DZC)

A form of digital output control in which the output on/off state is calculated for e very ac line c ycle.

Power is switched at the zero cross, which reduces electrical noise. See also Zero Cross.

DZC

See Distributed Zero Crossing.

Emissivity

The ratio of radiation emitted from a surf ace compared to radiation emitted from a blackbody at the same temperature.

Engineering Units

Selectable units of measure, such as de grees Celsius or F ahrenheit, pounds per square inch, ne wtons per meter, gallons per minute, liters per minute, cubic feet per minute or cubic meters per minute.

E

Earth Ground

A metal rod, usually copper , that provides an electrical path to the earth, to pre vent or reduce the risk of electrical shock.

EIA/TIA

Electronic Industries Alliance (EIA) and Telecommunications Industry Association (TIA). See also Serial

Communications.

EIA/TIA-232

—

A standard for interface between data terminal equipment and data communications equipment for serial binary data interchange. This is usually for communications over a short distance

(50 feet [15 m] or less) and to a single device.

EIA/TIA-485

—

A standard for electrical characteristics of generators and recei vers for use in balanced digital multipoint systems. This is usually used to communicate with multiple de vices over a common cable or where distances o ver 50 feet (15 m) are required.

Electrical Noise

See Noise.

Electromagnetic Interference (EMI)

Electrical and magnetic noise imposed on a system.

There are many possible causes, such as switching ac power inside the sine w ave. EMI can interfere with the operation of controllers and other devices.

Electrical-Mechanical Relays

See Relay, Electromechanical.

F

Fahrenheit

The temperature scale that sets the freezing point of water at 32° F and its boiling point at 212° F at standard atmospheric pressure. The formula for con version to Celsius is °C = 5/9 (°F - 32).

Failed Sensor Alarm

Warns that an input sensor no longer produces a v alid signal.

Filter

Filters are used to handle v arious electrical noise problems.

Digital Filter

—

A filter that sl ws the response of a system when inputs change unrealistically or too fast. Equi valent to a standard resistor -capacitor

(RC) filte

Digital Adaptive Filter

—

A filter that reject high frequency input signal noise (noise spikes).

Heat/Cool Filter

—

A filter that sl ws the change in the response of the heat or cool output. The output responds to a step change by going to approximately 2/3 its final alue within the numbers of scans that are set.

Frequency

The number of cycles over a specified period of time usually measured in c ycles per second. Also referred to as Hertz (Hz).

G

Gain

The amount of amplification used in an electrical ci cuit. Gain can also refer to the proportional (P) mode of PID.

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Global Alarm

Warns that one or more alarm conditions exist by activating a digital output.

Ground

An electrical line with the same electrical potential as the surrounding earth. Electrical systems are usually grounded to protect people and equipment from shocks due to malfunctions. Also referred to as

“safety ground.”

Input Scaling

The con verting of input signals to the engineering units of the process variable.

Input Type

The signal type that is connected to an input, such as thermocouple, RTD or process.

H

Hertz (Hz)

Frequency, measured in cycles per second.

Instance

An object that is an occurance of a class. Each instance of a DeviceNet object can have unique values for its attrib utes and can be e xamined or changed using the instance services. Class services are used to examine and change class attrib utes, which af fect all instances. Instance services are used to e xamine and change instance attributes which affect only that par ticular instance.

High Deviation Alarm

Warns that the process has risen more than a certain amount abo ve set point. It can be used as either an alarm or control function.

Integral Control (I)

Control action that automatically eliminates of fset, or droop, between set point and actual process temperature.

High Power

(As defined by Watlow Anafaze) Any voltage above

24 Vac or Vdc and any current level above 50 mAac or mAdc.

High Alarm

A signal that is associated with a set maximum v alue that can be used as either an alarm or boost control function.

HMI

Human-machine interface.

J

Job

A set of operating conditions for a process that can be stored and recalled in a controller’ s memory . Also called a recipe.

Junction

The point where two dissimilar metal conductors join to form a thermocouple.

Hysteresis

Control Hysteresis

—

The range through which a variation of the input produces no noticeable change in the output. In the hysteresis, specific con ditions can be placed on control output actions.

Operators select the hysteresis. It is usually abo ve the heating proportional band and belo w the cooling proportional band.

Process Hysteresis

—

In heat/cool applications, the +/- dif ference between heat and cool. Also known as process deadband.

K

Keypad Lock

A feature that pre vents operation of the k eypad by unauthorized people.

L

Lag

The delay between the output of a signal and the response of the instrument to which the signal is sent.

I

Input

Analog Input

— An input that accepts process variable information.

Digital Input

— An input that accepts on and of f signals.

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Linearity

The deviation in response from an e xpected or theoretical straight line v alue for instruments and transducers. Also called linearity error.

Load

The electrical demand of a process, e xpressed in power (Watts), current (Amps) or resistance (Ohms).

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The item or substance that is to be heated or cooled.

Low Deviation Alarm

Warns that the process has dropped more than a cer tain amount belo w set point. It can be used as either an alarm or control function.

On/Off Control

A method of control that turns the output full on until set point is reached, and then off until the process differs from the set point by more than the hysteresis.

Open Loop

A control system with no sensory feedback.

Low Alarm

A signal that is associated with a set minimum v alue that can be used as either an alarm or boost control function.

M

Manual Mode

A selectable mode that has no automatic control aspects. The operator sets output levels.

Optical Isolation

Two electronic netw orks that are connected through an LED (Light Emitting Diode) and a photoelectric receiver. There is no electrical continuity between the two networks.

Output

Control signal action in response to the dif ference between set point and process variable.

Manual Reset

A parameter that allows the user to eliminate offset or droop between set point and actual process temperature. See also Integral.

Output Type

The form of control output, such as time proportioning, distributed zero crossing, Serial D AC or analog.

Also the description of the electrical hardw are that makes up the output.

Milliampere (mA)

One thousandth of an ampere.

Overshoot

The amount by which a process v ariable exceeds the set point before it stabilizes.

N

Noise

Unwanted electrical signals that usually produce signal interference in sensors and sensor circuits. See also Electromagnetic Interference.

P

PID

Proportional, Inte gral, Deri vative. A control mode with three functions: Proportional action dampens the system response, inte gral corrects for droops, and derivative prevents overshoot and undershoot.

Noise Suppression

The use of components to reduce electrical interfer ence that is caused by making or breaking electrical contact, or by inductors.

Polarity

The electrical quality of ha ving tw o opposite poles, one positive and one negative. Polarity determines the direction in which a current tends to fl w.

O

Object

An object is a softw are programming concept in which data and functionality are associated with vir tual objects. DeviceNet objects consists of data called attributes and functions called services. Services are used to examine or change attribute values.

Process Input

A v oltage or current input that represents a straight line function.

Process Variable (PV)

The parameter that is controlled or measured. Typical examples are temperature, relative humidity, pressure, fl w, fluid l vel, events, etc.

Offset

The difference between the set point and the actual value of the process variable. Offset is the error in the process v ariable that is typical of proportional-only control.

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Proportional (P)

Output effort proportional to the error from set point.

For example, if the proportional band is 20° and the process is 10° belo w the set point, the heat propor tioned effort is 50 percent. The lower the PB v alue, the higher the gain.

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Proportional Band (PB)

A range in which the proportioning function of the control is acti ve. Expressed in units, de grees or per cent of span. See also PID.

Proportional Control

A control using only the P (proportional) value of PID control.

Pulse Input

Digital pulse signals from de vices, such as optical encoders.

PV

See Process Variable.

R

Ramp

A programmed increase in the temperature of a set point system.

Range

The area between tw o limits in which a quantity or value is measured. It is usually described in terms of lower and upper limits.

Recipe

See Job.

Relay

A switching device.

Electromechanical Relay

—

A power switching device that completes or interrupts a circuit by physically mo ving electrical contacts into contact with each other. Not recommended for PID control.

Solid State Relay (SSR)

— A switching de vice with no moving parts that completes or interrupts a circuit electrically.

Reset

See Automatic Reset, Manual Reset.

Resistance

Opposition to the fl w of electric current, measured in

Ohms.

Resistance Temperature Detector (RTD)

A sensor that uses the resistance temperature characteristic to measure temperature. There are tw o basic types of RTDs: the wire RTD, which is usually made of platinum, and the thermistor , which is made of a semiconductor material. The wire R TD is a positi ve temperature coef ficient sensor onl , while the ther mistor can have either a negative or positive temperature coefficient

Reverse Action

An output control action in which an increase in the process variable causes a decrease in the output. Heating applications usually use reverse action.

RTD

See Resistance Temperature Detector.

S

Serial Communications

A method of transmitting information between devices by sending all bits serially o ver a single communication channel.

Set Point (SP)

The desired v alue of the process v ariable. For example, the temperature at which a system is to be maintained.

Shield

A metallic foil or braided wire layer surrounding conductors that is designed to pre vent electrostatic or electromagnetic interference from external sources.

Signal

Any electrical transmittance that conveys information.

Solid State Relay (SSR)

See Relay, Solid State.

Span

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

Stability

The ability of a de vice to maintain a constant output with the application of a constant input.

T

Thermistor

A temperature-sensing device made of semiconductor material that exhibits a large change in resistance for a small change in temperature. Thermistors usually have negative temperature coefficients, although th y are also a vailable with positi ve temperature coef fi cients.

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Thermocouple (T/C)

A temperature sensing de vice made by joining tw o dissimilar metals. This junction produces an electrical voltage in proportion to the dif ference in temperature between the hot junction (sensing junction) and the lead wire connection to the instrument (cold junction).

Thermocouple Extension Wire

A grade of wire used between the measuring junction and the reference junction of a thermocouple. Extension wire and thermocouple wire have similar properties, but extension wire is less costly.

Transmitter

A device that transmits temperature data from either a thermocouple or RTD by way of a two-wire loop. The loop has an e xternal po wer supply . The transmitter acts as a variable resistor with respect to its input signal. Transmitters are desirable when long lead or extension wires produce unacceptable signal degradation.

U

Undershoot

The amount by which a process v ariable falls below the set point before it stabilizes.

V

Volt (V)

The unit of measure for electrical potential, voltage or electromotive force (EMF). See also Voltage.

Voltage (V)

The dif ference in electrical potential between tw o points in a circuit. It is the push or pressure behind current fl w through a circuit. One volt (V) is the difference in potential required to mo ve one coulomb of charge between two points in a circuit, consuming one joule of energy. In other w ords, one volt (V) is equal to one ampere of current (I) fl wing through one ohm of resistance (R), or V = IR.

Z

Zero Cross

Action that provides output switching only at or near the zero-voltage crossing points of the ac sine wave.

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