38 Questions
What is the primary function of actuation systems?
To transform output from a microprocessor into a controlling action
What is a disadvantage of hydraulic systems compared to pneumatic systems?
Higher cost
What is the purpose of an accumulator in a hydraulic system?
To smooth out short-term fluctuations in oil pressure
What type of pump is used to provide pressurized oil in a hydraulic system?
Gear pump
What is a common type of hydraulic pump?
All of the above
What is the source of power for a hydraulic pump?
Electric motor
What is a potential hazard associated with hydraulic systems?
Oil leaks
What is the purpose of a non-return valve in a hydraulic system?
To prevent backflow of oil
What is a characteristic of servo valves?
Accurate position control
What type of system is a servo valve often used in?
Closed-loop control system
What is the advantage of servo valves in hydraulic systems?
Higher reliability
What is a characteristic of proportional control valves?
Less expensive
What is the purpose of process control valves?
To control the rate of fluid flow
What is a characteristic of servo valves in terms of flow?
It can give a continuous variation of flow
What is a characteristic of servo valves in terms of responsiveness?
Highly responsive
What is a characteristic of servo valves in terms of repeatability?
High repeatability
What happens to a transistor when the input voltage is sufficiently high?
Very little of the VCC voltage appears at the output
What is the voltage called that is applied to the base of an NPN transistor?
VBE
What is the purpose of making the collector more positive than the emitter in an NPN transistor?
To allow the transistor to function
What is the main advantage of using a Darlington pair configuration?
It is used for higher power requirements or more amplification
What does a MOSFET stand for?
Metal-Oxide-Semiconductor Field-Effect Transistor
What is one of the functions of a MOSFET?
To switch a circuit on and off based on voltage
What is the purpose of a MOSFET in electronic devices?
To act as an electronic switch and amplify signals
What is the typical application of a MOSFET?
In modern electronic devices
What is the basic principle of operation of a 2-way ball valve?
The ball is rotated 90 degrees to open and close the valve.
What is the purpose of the seats in a 2-way ball valve?
To lead the inlet and outlet of the fluid flow.
What is unique about the obstructer in a butterfly valve?
It is a thin disc.
What is the advantage of butterfly valves compared to ball and plug valves?
They are lighter and less expensive.
What is the primary use of butterfly valves?
As a basic on/off valve.
In what position is the flow of fluid completely blocked in a butterfly valve?
When the disc is perpendicular to the flow.
What is the primary function of finite position valves?
To switch actuators on or off
What is the main characteristic of infinite position valves?
They can control flow anywhere between fully on and fully off
What is the primary function of directional control valves?
To direct the flow of fluid through a system
What is a common type of directional control valve?
Spool valve
What is the normal condition of a poppet valve?
Normally closed
What do arrow-headed lines indicate in valve symbols?
The direction of flow in each position
What do blocked-off lines indicate in valve symbols?
Closed flow lines
What is the label for the pressure supply port in valve symbols?
1 or P
Study Notes
Actuation Systems
- Actuation systems transform the output of a microprocessor or control system into a controlling action on a machine or device.
Hydraulic Systems
- Hydraulic systems can be used for high-power control devices but are more expensive than pneumatic systems and have hazards associated with oil leaks.
- Pressurized oil is provided by a pump driven by an electric motor, and an accumulator smooths out short-term fluctuations in output oil pressure.
- Commonly used hydraulic pumps include gear pumps, vane pumps, and piston pumps.
Directional Control Valves
- Directional control valves are used to direct the flow of fluid through a system in pneumatic and hydraulic systems.
- Common types of directional control valves include spool valves and poppet valves.
- Valve symbols use arrow-headed lines to indicate flow directions, with blocked-off lines indicating closed flow lines.
Servo and Proportional Control
- Servo valves are capable of infinitely variable positioning and controlling the direction and amount of flow.
- They have internal feedback for better valve operation with high reliability.
- Proportional control valves are less expensive and have the spool position directly controlled by the size of the current to the valve solenoid.
- Characteristics of servo valves include:
- Higher oil capacity
- Accurate position control
- Closed-loop control system
- Continuous variation of flow with changing input signal
- Highly responsive
- High repeatability
- High frequency response
- Perfect flow changes handling
Process Control Valves
- Process control valves control the rate of fluid flow and are used in applications such as controlling the rate of flow of a liquid into a tank.
- 2-way ball valves are extremely common and simple in design, with a ball that rotates to open or block the flow.
- 3-way ball valves are also available.
Butterfly Valves
- Butterfly valves operate by rotating an obstructer 90 degrees from open to closed position.
- The obstructer is a thin disc that turns sideways to open, and the flow travels around the disc when rotated 90 degrees.
- These valves are commonly used as basic on/off valves, but are also suited for proportional flow control by stopping the disc at intermediate positions.
Transistors
- NPN BJT (Bipolar Junction Transistor) has a collector, emitter, and base.
- When a voltage is applied to the base, the transistor turns on, allowing current to flow from the collector to the emitter.
- Darlington pair configuration is used for higher power requirements or when more amplification is needed.
MOSFETs
- A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a type of transistor widely used in electronics for switching and amplifying signals.
- Functionality includes switching (turning a circuit on and off) and amplification (controlling the flow of current between the drain and source terminals).
This chapter covers the basics of actuation systems, including interpretation and design of sequential control systems, hydraulic and pneumatic directional control valves, and cylinders, as well as process control valves and their characteristics.
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