Then we introduce the concepts of the Integral (I) and Derivative (D) functions, and explain their essential role in optimizing closed loop control performance for PID controllers. Once set up, the loop must maintain its optimum performance even during unpredictable and changing process conditions.īelow, we look at how proportional control systems operate, and how their performance can be assessed. It is usually desirable if not essential to achieve the fastest possible response time and greatest steady-state accuracy, without creating a risk of instability. However, designing and optimizing a control loop for a particular application is not without some challenges.

Proportional control is a continuous control method that offers more nuanced, robust and better quality performance than the relatively crude on/off approach.

Conversely, if the hysteresis gap is too wide, the room temperature will be sub-optimal for much of the time.Īdditionally, in some industrial systems, a sudden and full load turn-on could lead to issues with inrush currents. This exposes the limitations of on/off control without hysteresis, the thermostat would switch continuously, which may cause excessive wear and tear, and possibly intrusive audible noise. This could typically be 4☌, so for a setpoint of 20☌, the thermostat turns on at 18☌ and below, and off at 22☌ and above. Practical thermostats have a hysteresis, or dead-band. If the temperature exceeds the SP, the heating will be turned off, and, possibly, air conditioning will be started for active cooling. If the temperature is too low, it turns on the central heating to heat the room until it reaches SP temperature. The system uses the MV feedback to close the loop. The thermostat compares the room temperature measured value (MV) with its setpoint (SP) as adjusted by its user. On/off or ‘Bang-Bang’ control - this is the simplest form of closed loop control, and is exemplified by a domestic heating system with a room thermostat. Although the tap can be operated by a user to regulate water flow, the hose has no feedback mechanism to ‘close the loop’ for automatic regulation. One example is a garden hose, connected to a tap. Then, we focus in on PID controllers and how they operate. Accordingly, we start by explaining the control system hierarchy that exists today, and showing how PID control fits into this.

However, they come in many types, of which PID control is just one, albeit the most sophisticated. (Source: Adobe Stock) A control system hierarchyĬontrol systems are ubiquitous in industrial, medical, military, automotive, utility and many other applications - and sometimes appear in our daily lives.

Pid controller labview