• 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.