ac vocabulary terms and definitions

Question 1

How an indicated value conforms to an accepted standard value
or true value. Normally “reference accuracy” is used which defines
the limit that errors will not exceed when the device is used under
reference operating conditions. Reference accuracy is normally
expressed in a number of forms typically preceded by a+ and a -
sign. e.g. ±0.1 °C, ± 2% of scale length. (Do not confuse with
precision)

Answer 1

ACCURACY

Question 2

Analogue to digital converter

Answer 2

ADC

Question 3

signal representing a variable which may be
continuously observed and continuously represented.
i.e. The signal has an infinite number of points between
any two values.

Answer 3

ANALOGUE SIGNAL

Question 4

decrease in signal magnitude. Also, the reciprocal of gain.

Answer 4

ATTENUATION

Question 5

A signal path which includes a forward path, a feedback path,
and a summing point , and forms a closed circuit.

Answer 5

CLOSED LOOP

Question 6

The parameter that is
desired to be controlled, e.g. temperature, flow rate,
pressure, liquid level.

Answer 6

CONTROLLED VARIABLE /PROCESS VARIABLE

Question 7

A device which operates automatically to regulate a controlled
variable. In process industries controller always means
“automatic “ but other industries the automatic is not implied so
the term “automatic controller’’ is used.

Answer 7

CONTROLLER

Question 8

Digital to analogue converter

Answer 8

DAC

Question 9

Distributed control system. Using DOC and Supervisory control for
process control sharing a common communications facility(Data
Highway)

Answer 9

DCS

Question 10

A building automation system in which
a microprocessor based control system performs building automation
digitally.

Answer 10

Distributed(Direct) Digital Control

Question 11

control action in which the output is
proportional to the rate of change of
the input.

Answer 11

DERIVATIVE (RATE) CONTROL ACTION

Question 12

The range through which an input can be varied without initiating
an observable response

Answer 12

DEAD-BAND

Question 13

information represented by a set of discrete values. The
values being represented by numbers

Answer 13

DIGITAL SIGNAL

Question 14

in a control loop, it is the variable which
is sensed to originate a feed-back
signal.

Answer 14

DIRECTLY CONTROLLED VARIABLE

Question 15

This is the signal derived in a closed loop control system from
the difference between the set-point signal and the feed-back
signal.

Answer 15

ERROR SIGNAL

Question 16

• A component of a device or system.

Answer 16

ELEMENT

Question 17

The-return signal which is generated from the
measurement of the directly controlled variable.

Answer 17

FEED-BACK SIGNAL

Question 18

{final controlling element)- It is the forward
controlling element which directly changes the
value of the manipulated variable.

Answer 18

FINAL CONTROL ELEMENT-

Question 19

the ratio of the change in output due to proportional
control action to the change in input.

Answer 19

GAIN, PROPORTIONAL

Question 20

control action in which the output is
proportional to the time integral of
the input. In other words, the rate of
change of the output is proportional
to the input.

Answer 20

INTEGRAL (RESET) CONTROL ACTION

Question 21

A quantity or condition which is varied as a
function of the actuating error signal so as to
change the value of the directly controlled variable.

Answer 21

MANIPULATED VARIABLE

Question 22

NTC

Answer 22

Negative temperature coefficient.

Question 23

a signal path without feedback.

Answer 23

OPEN LOOP

Question 24

PROCESS

Answer 24

Physical or chemical change of matter or conversion of energy. e.g.
change in temperature, pressure, electrical potential, speed etc.

Question 25

control action in which there is a
continuous linear relation between the
output and the input.

Answer 25

PROPORTIONAL CONTROL ACTION

Question 26

RANGE

Answer 26

the region between two limits within a quantity is transmitted,
measured, or received. It is expressed by stating the upper and lower
range values. e.g. -20 to 150 °C

Question 27

the element which directly responds to the
measured variable

Answer 27

SENSING ELEMENT (SENSOR)

Question 28

An input variable which determines the desired value of the
controlled variable. It may be set manually, automatically set or
programmed.

Answer 28

SET-POINT

Question 29

SPAN

Answer 29

The algebraic difference between the upper and lower range values. If
the range were -20 to 200°C, the Span would be 220°C.

Question 30

TRANSDUCER

Answer 30

A device or element which converts energy from one type to
another.

Question 31

TRANSMITTER

Answer 31

A transducer which responds to a measured variable by
means of the sensor (sensing element) and converts it to a
standardized transmission signal .