ANALOG CONTROL SYSTEM

Analog control system is a control system that uses analog signals in the form of continuous physical signals such as voltage, current, pressure or mechanical position to control or regulate a process or system. The controller output varies smoothly over time in direct over time in direct proportion to some physical quantity or input.

The main types of analog control system are; proportional, integral, derivative and proportional integral derivative control system.

Proportional (P) control systems use a proportional controller to control or regulate the output. The controller adjusts the output in proportion to the error signal, which is the difference between the desired set point and the actual process value. Example of proportional (P) control system includes; simple DC motor speed control, water level float valve, op-amp headlight dimmer/light following circuit etc.

Integral (I) control systems uses an integral controller to regulate or control the output. The controller adjusts the output based on the accumulation of past error values. Example of integral (I) control system includes; analog integrator temperature holding circuit, op-amp based battery charge controller, voltage regulator “trim” stage etc.

Derivative (D) control systems use a derivative controller to regulate or control the output. The controller adjusts the output based on the rate of change of the error signal. Example of derivative (D) control system includes; anti-slam damping circuit in servo systems, op-amp differentiator in audio limiter/compressor side chains, anti-vibration circuit in analog camera stabilizer etc.

Proportional integral derivative (PID) control systems combine the features of proportional, integral and derivative Control systems to regulate or control the output. Example of proportional integral and derivative PID) control systems includes; classic analog PID temperature controller (op-amps based), analog servo motor position controller, cruise control (early analog automotive systems), power supply voltage regulation (linear PID feedback loop) etc.

The advantages of analog control systems are; analog control systems provide smooth control of the process which is essential in applications where precise control is required. Analog control systems can provide high resolution which means they can detect and respond to smaller changes in the process. Analog control systems are less expensive than digital control systems especially for simple applications. Analog control systems are less susceptible to noise and interference than digital control systems.

The disadvantages of analog control systems are; analog control systems have limited accuracy which can be a problem in applications where accurate or precise control is required. Analog control systems can drift over time which means that the output can change even if the input remains constant. Analog systems can be susceptible to noise and interference which can affect their performance. Analog control systems can be difficult to modify or reconfigure which can limit their flexibility.

Analog control systems find applications in the following; industrial process control of temperature, pressure, fluid etc. HVAC thermostats of bimetallic and electronic analog origin. Audio amplifiers, equalization, power supply voltage and current regulation, servo motor control in robotics and manufacturing and analog autopilot systems etc. analog control systems are also used in medical devices such as pacemakers, insulin pumps and ventilators.

The future of analog control systems is based on the advances and development of the following technologies; analog control systems are increasingly integrated with digital control systems to form a hybrid system which allows for more advanced control strategies and improved performance. Advances in technology such as high speed/low latency niches in RF and power electronics switching and AI,ML and xeromorphic and analog computing integration will pave the way for more efficient and reliable analog control system. Analog backup controllers will still be used in aerospace and nuclear control systems as fail-safe independent of software failures. Though pure analog control is steadily being replaced by digital and hybrid systems such as DSP based PID, micro controller driven control loops, because of the obvious digital control system characteristics, but despite this trend analog control system will remain with us for a very long time.

 

SORCES:

• Control systems engineering by Norman S. Nise.
• Analog and digital control systems by Robert C. Dorf and Richard H. Bishop.
• Automatic control systems by Benjamin C. Kuo and Farid Golnaraghi.
• Analog electronics for scientific application by Dennis Barnaal.
• Control systems for practicing engineers by David C. Swanson.