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Accuracy : Accuracy is the measurement tolerance of the instrument and defines the
limits of the errors made when the instrument is used in normal operating conditions.
Sensitivity : The parameters of control system are always changing with change in
surrounding conditions, internal disturbance or any other parameters.
Noise : An undesired input signal is known as noise. A good control system should be
able to reduce the noise effect for better performance.
Stability : For the bounded input signal, the output must be bounded and if input is
zero then output must be zero then such a control system is said to be stable system.
Bandwidth : An operating frequency range decides the bandwidth of control system.
Bandwidth should be large as possible for frequency response of good control system.
Speed : It is the time taken by control system to achieve its stable output. A good
control system possesses high speed. The transient period for such system is very small.
Oscillation : A small numbers of oscillation or constant oscillation of output tend to
system to be stable.
Points to record : Characteristics
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Multivariable Control System
Open-Loop Control Systems utilize a controller or control
actuator to obtain the desired response.
to compare the
actual output to
Control System – Types
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An accurate positioning motor, with power amplifier (we’ll see how to make these
later in the course) that accepts a low-power (almost no current) voltage signal, and
moves the accelerator pedal in a manner proportional to the voltage signal.
• The engine, which produces a torque that is related to the position of the
accelerator pedal (current and past values).
• The drivetrain of the car, which transmits this torque to the ground through the
• A vehicle, which gets accelerated due to the forces (road/tire interface,
aerodynamic) which act on it. • Changes in the slope of the highway, which act as a
disturbance force on the car. We do not assume that the car has a sensor which can
measure this slope.
• A speedometer, which converts the speed (in miles/hour, say), into a voltage signal
for feedback purposes.
CRUISE CONTROL – A simple case study
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Cruise control – Closed loop
• Because of the hill, the speed of the car changes
• The controller, measuring the actual speed, and the desired speed,
detects an error in the speed regulation
• The controller compensates for the error by adjusting the output voltage,
which moves the throttle into a new position, compensating for the
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Adaptive Cruise control – Closed loop
• Adaptive cruise control (ACC) is an intelligent form of cruise control that
slows down and speeds up automatically to keep pace with the car in
front of you.
• The driver sets the maximum speed
• Then a radar sensor watches for traffic ahead, locks on to the car in a
lane, and instructs the car to stay 2, 3, or 4 seconds behind the person car
ahead of it (the driver sets the follow distance, within reason).
• ACC is now almost always paired with a pre-crash system that alerts you
and often begins braking
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• To use adaptive cruise control, you start the same as you would with
standard cruise control.
• The driver turns ACC on, accelerates to the desired speed, then presses
the “Set” button.
• It’s then possible to tweak the “+” and “-” buttons to raise or lower the
speed, typically by in 1 or 5 mph increments.
• Lastly, the driver can set the desired gap behind the next car, most
commonly by pressing a button to cycle among short, medium, and long
• Some automakers show icons with 1, 2 or 3 distance bars between two
• An indicator in the instrument panel or head-up display shows a car icon
and often what looks like converging-at-infinity lines, indicating the
roadway. When radar detects a car ahead, a second car icon appears or
the lone car icon changes color.