Where are automated controls most common?
commercial and industrial applications
List examples of an automated control system
- Cruise Control
- HVAC
- Food Production
- PF correction
- Autopilot for ships and aircrafts
List benefits of automated controls
- Consistent
- Reduced labour (initial labour is usually much higher)
- Improved safety
- Lower operating cost
What are the two categories for AC?
Open Loop and Closed Loop
Open loop characteristics and examples of applications?
- Requires an operator
- not self correcting
- no feedback
- Bathroom heat lamp
- Heat and a/c for most cars
Closed loop characteristics and examples?
- no operator required
- self correcting
- has feedback
- Bathroom baseboard heat
- climate control in some cars
advantages and disadvantages of open loop?
Advantages:
- Low initial cost
- easy to install
- simple to troubleshoot
Disadvantages:
- ongoing labour
- error
Closed loop advantages and disadvantages?
Advantages:
- self correcting
- reduced ongoing labour costs
- reduced error
- higher performance
Disadvantages:
- High initial cost
- expensive to install
- more complex to troubleshoot
What is the error signal?
the difference between the set point and sensor signals
Examples of process variables?
- temperature
- level
- pressure
- speed
- light
- flow
- weight
What are the two modes of control for each category?
- Discontinuous
2. Continuous
What do discontinuous controls use and what are the characteristics? How is the process variable corrected?
- Use actuators which are either on or off
- corrected by varying the time intervals in which the actuator is on or off
In discontinuous control, the process variable error can be substantial if the ___________ is too wide
Dead Band
In continuous control, the actuator output is ________________________________________?
variable and proportional to the difference between the set point and the sensor.
Are the sensors in continuous control analog or digital? Why?
Analog, because their output can vary continuously
What is the process variable error dependant on?
- RESOLUTION of the sensors
- PERFORMANCE of the actuators
- COMPLIANCE of the process variable
what does the “PID” stand for in PID control?
- Proportional
- Integral
- Derivative
What are P & ID Drawings, what do they include and which block diagram is it?
- Piping and Instrumentation Drawings
- Pipes, pumps, tanks, sensors, actuators, controllers, etc…
- Process control block diagrams
What does the first and then remaining letters stand for in a P & ID balloon
First letter = Process Variable
Next letters = instrument
List the methods and what they mean in PID Control
Proportional = "How BIG is the error?" Integral = "How Long has the error been present?" Derivative = "How FAST is the error changing?"
What are sensors also known as?
Transducers
What does a transducer do?
Converts one form of energy to another
What do active transducers do? list an example
- Generate output without an external supply
- a thermo couple which generates a small voltage when heated up
What do passive transducers do? list an example
- Do not generate an output
- only physically or electrically change
- a resistive thermal device changes resistance with temperature
