ac vocabulary terms and definitions Flashcards
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)
ACCURACY
Analogue to digital converter
ADC
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.
ANALOGUE SIGNAL
decrease in signal magnitude. Also, the reciprocal of gain.
ATTENUATION
A signal path which includes a forward path, a feedback path,
and a summing point , and forms a closed circuit.
CLOSED LOOP
The parameter that is
desired to be controlled, e.g. temperature, flow rate,
pressure, liquid level.
CONTROLLED VARIABLE /PROCESS VARIABLE
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.
CONTROLLER
Digital to analogue converter
DAC
Distributed control system. Using DOC and Supervisory control for
process control sharing a common communications facility(Data
Highway)
DCS
A building automation system in which
a microprocessor based control system performs building automation
digitally.
Distributed(Direct) Digital Control
control action in which the output is
proportional to the rate of change of
the input.
DERIVATIVE (RATE) CONTROL ACTION
The range through which an input can be varied without initiating
an observable response
DEAD-BAND
information represented by a set of discrete values. The
values being represented by numbers
DIGITAL SIGNAL
in a control loop, it is the variable which
is sensed to originate a feed-back
signal.
DIRECTLY CONTROLLED VARIABLE
This is the signal derived in a closed loop control system from
the difference between the set-point signal and the feed-back
signal.
ERROR SIGNAL
- A component of a device or system.
ELEMENT
The-return signal which is generated from the
measurement of the directly controlled variable.
FEED-BACK SIGNAL
{final controlling element)- It is the forward
controlling element which directly changes the
value of the manipulated variable.
FINAL CONTROL ELEMENT-
the ratio of the change in output due to proportional
control action to the change in input.
GAIN, PROPORTIONAL
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.
INTEGRAL (RESET) CONTROL ACTION
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.
MANIPULATED VARIABLE
NTC
Negative temperature coefficient.
a signal path without feedback.
OPEN LOOP
PROCESS
Physical or chemical change of matter or conversion of energy. e.g.
change in temperature, pressure, electrical potential, speed etc.
control action in which there is a
continuous linear relation between the
output and the input.
PROPORTIONAL CONTROL ACTION
RANGE
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
the element which directly responds to the
measured variable
SENSING ELEMENT (SENSOR)
An input variable which determines the desired value of the
controlled variable. It may be set manually, automatically set or
programmed.
SET-POINT
SPAN
The algebraic difference between the upper and lower range values. If
the range were -20 to 200°C, the Span would be 220°C.
TRANSDUCER
A device or element which converts energy from one type to
another.
TRANSMITTER
A transducer which responds to a measured variable by
means of the sensor (sensing element) and converts it to a
standardized transmission signal .
