Final Correcting Devices and Amplifiers Flashcards
In a closed-loop system, _____ is
a valve or a valve like device that varies the flow of a fluid into the process
final correcting devices and amplifiers
It is very often an electric motor and may be also a solenoid valve, a pneumatic actuated valve , a damper, an SCR or a triac.
final correcting devices and amplifiers
where the heat input into the process is varied by adjusting a valve which controls the flow of combustion air or of liquid or gaseous fuel.
Temperature-control processes
where the pressure is usually corrected by changing a valve opening on either the inlet side or the outlet side of the process.
Pressure-control processes
the process variable that needs to be measured and controlled to a desired value.
Controlled Variable
is a quantity which is varied so as to affect the value of the controlled variable or
quantities that are directly adjusted to control the system.
Manipulated Variable
is an electromechanically
operated valve. It differ in the characteristics of the electric current they use, the strength of the magnetic field they generate, the mechanism they use to regulate the fluid, and
the type and characteristics of fluid they control.
solenoid valve
Usage of solenoid valve
- On-Off Control Mode
- Voltage Compatibility
It is preferred for situations where the valve itself is large and in cases where the valve must operate against high fluid
pressure ensuring reliable and precise control of fluid or gas flow in industrial and process control applications.
Two-Position Electric
Motor-Driven Valves
Two-Position Electric
Motor-Driven Valves is mostly operated in ____.
unidirectional split-phase induction motor
A three-position controller that has three output signals instead of only two. These output signals are:
1. The measured value is too
low, so drive the valve ____.
2. The measured value is too
high, so drive the valve ____.
3. The measured value is within
the _____, so don’t
drive the valve at all but just
let it sit where it is.
open, closed, differential gap
It is a method of positioning a
control valve at any intermediate position. The usual method is to connect the
valve to a reversible slow-speed
induction motor.
Proportional-Position
Electric Motor-Driven Valves
In cases involving large valves, electric motor drives may not be suitable due to the valve’s significant inertia and high
breakaway friction. In such situations, these valves are typically operated using
pneumatic or hydraulic pressure instead of electric motors for positioning
Electropneumatic Valves
Electropneumatic Valves often referred to as an ______,
which is a device used to
control the position and
operation of pneumatic valves
using electrical signals
electropneumatic actuator or
electropneumatic positioner
Its primary function is to
convert electrical signals into
pneumatic signals to precisely
control the position of a
pneumatic actuator, such as a
control valve.
Electropneumatic Signal Converter Driving a Pneumatic
Positioner
It is the best actuator in control situations where the valve or damper is very massive, or where it is difficult to hold the valve in a steady position due to a large irregular forces exerted by the moving fluid
Hydraulic Positioner
switching devices used
to control a circuits, a
low power devices or
multiplying the number
of contacts available.
relay
switching devices used
to switch on/off heavy
electrical loads such as
electric motors,
power factor, etc.
contactor
When electric current is the
manipulated variable in a closed loop control system, the final correcting devices is often a ________.
Example: Electric heating process
relay or contactor
There is a differential gap for On-Off control: hysteresis effect
relay hysteresis
This basically On-Off control, except that the Off position is
not really complete Off.
A THREE-PHASE CONTACTOR SWITCHING BETWEEN DELTA AND WYE
Can also be used in On-Off systems, replacing relays and contactors. Serve as the control device in closedloop and many open-loop systems.
Thyristor
In modern control systems, power thyristors, namely, _____, are used as final correcting devices.
SCRs and triacs
Current to the load is continuously variable, and there is built-in comparison between measured value and
set point to bring automatic adjustment of the current
Closed-loop system
