Lag Time
Lag time is the delay between the application of an input to a control system and the occurrence of the corresponding output. This delay can affect the performance and stability of a system.
Example: In a heating system, lag time might refer to the delay between turning on a furnace and observing a rise in room temperature.
Dead Time
Dead time is the time delay from when a change in the input signal occurs until the first sign of a response is observed in the output.
Example: In a distillation column, dead time could be the delay between changing the feed composition and detecting a change in product composition.
Dead Band
Dead band refers to a range within which no action is taken by the control system. This is often used to prevent excessive response due to minor fluctuations near the set point.
Example: A thermostat may have a dead band around the set temperature to avoid continuous cycling of the heating or cooling system.
Set Point
The set point is the desired or target value for the controlled variable that the system aims to maintain.
Example: In a temperature control system, the set point might be the target room temperature.
Error Signal
The error signal is the difference between the set point and the measured value of the controlled variable. It is a critical component in feedback systems.
Example: If the set point is 22°C and the actual temperature is 20°C, the error signal would be 2°C.
Transient
Transients are the temporary states that occur following a change in the system’s operating conditions, before reaching a new steady state.
Example: The surge in engine speed when an accelerator pedal is initially pressed is a transient.
Measured Variable
The measured variable is the actual value of a parameter being controlled, detected by sensors in the system.
Example: In a flow control system, the measured variable could be the flow rate as detected by a flow meter.
Controlled Variable
The controlled variable is the quantity or condition that is regulated by the control system to match the set point.
Example: In an air conditioning system, the controlled variable would be the room temperature.
Variable Range
The variable range refers to the span between the minimum and maximum values that a controlled or measured variable can assume.
Example: For a pH control system, the variable range might be 4 to 10.
Control Parameter Range
This is the range over which a control parameter can be adjusted to achieve the desired output.
Example: In a PID controller, the control parameter range could include the range of possible settings for proportional, integral, and derivative gains.
Offset
Offset is the steady-state difference between the set point and the actual value of the controlled variable when the system is supposed to be at equilibrium.
Example: In a temperature control system, if the set point is 25°C but the system consistently maintains 24°C, there is an offset of 1°C.
These concepts are foundational for designing and analysing control systems in various applications, ensuring they operate efficiently and respond accurately to changes in their environment.
