This document discusses PID controllers, their limitations, and applications. It notes that PID controllers can perform poorly for some applications, like non-linear systems. Their performance can be improved by combining feedback control with feed-forward control using system knowledge. It also discusses issues like gain settings, noise, and non-linearity. Applications mentioned include automatic control of temperature, flow, pressure and level in industrial processes, as well as examples in heating, drying, curing and baking.
This document discusses PID controllers, their limitations, and applications. It notes that PID controllers can perform poorly for some applications, like non-linear systems. Their performance can be improved by combining feedback control with feed-forward control using system knowledge. It also discusses issues like gain settings, noise, and non-linearity. Applications mentioned include automatic control of temperature, flow, pressure and level in industrial processes, as well as examples in heating, drying, curing and baking.
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A powepoint presentation in feedback & control system subject which talks about PID CONTROLLER.
This document discusses PID controllers, their limitations, and applications. It notes that PID controllers can perform poorly for some applications, like non-linear systems. Their performance can be improved by combining feedback control with feed-forward control using system knowledge. It also discusses issues like gain settings, noise, and non-linearity. Applications mentioned include automatic control of temperature, flow, pressure and level in industrial processes, as well as examples in heating, drying, curing and baking.
This document discusses PID controllers, their limitations, and applications. It notes that PID controllers can perform poorly for some applications, like non-linear systems. Their performance can be improved by combining feedback control with feed-forward control using system knowledge. It also discusses issues like gain settings, noise, and non-linearity. Applications mentioned include automatic control of temperature, flow, pressure and level in industrial processes, as well as examples in heating, drying, curing and baking.
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PROPORTIONAL INTEGRAL
DERIVATIVE CONTROL
LIMITATIONS OF PID CONTROL
& its APPLICATIONS
REPORTED BY: Princess Diana Dean A. Cutab
LIMITATIONS OF PID While PID controllers are applicable to many control problems, they can perform poorly in some applications. PI controller. PID controllers, when used alone can give poor performance, when the PID loop gains must be reduced so that the control system does not overshoot, oscillate or hunt about the control set point value. The control system performance can be improved by combining the feedback (or closed-loop) control of a PID controller with feed-forward (or open-loop) control. Knowledge about the system (such as the desired acceleration and inertia) can be fed forward and combined with the PID output to improve the overall system performance. If the proportional gain is too high, the system can become unstable. In contrast,a small gain results in a small output response to a large input error and a less responsive or less sensitive controller Block diagram of a process under PID Control The feed-forward value alone can often provide the major portion of the controller output. The PID controller can then be used primarily to respond to whatever difference or error remains between the set point (SP) and the actual value of the process variable (PV). Since the feed-forward output is not affected by the process feedback, it can never cause the control system to oscillate, thus improving the system response and stability. For example, in most motion control systems, in order to accelerate a mechanical load under control, more force or torque is required from the prime mover, motor, or actuator. If a velocity loop PID controller is being used to control the speed of the load and command the force or torque being applied by the prime mover, then it is beneficial to take the instantaneous acceleration desired for the load,scale that value appropriately and add it to the output of the PID velocity loop controller. This means that whenever the load is being accelerated or decelerated, a proportional amount of force is commanded from the prime mover regardless of the feedback value. The PID loop in this situation uses the feedback information to effect any increase or decrease of the combined output in order to reduce the remaining difference between the process set point and the feedback value. Working together, the combined open-loop feed-forward controller and closed-loop PID controller can provide a more responsive, stable and reliable control system. Another problem faced with PID controllers is that they are linear. Thus, performance of PID controllers in non-linear systems (such as HVAC systems) is variable. HVAC SYSTEM ➲ Heating, ventilation,and air conditioning (HVAC) is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is sub discipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. ➲ HVAC is important where safe and healthy building conditions are regulated with respect to temperature, humidity using fresh air from outdoors. Often PID controllers are enhanced through methods such as PID gain scheduling or fuzzy logic. Further practical application issues can arise from instrumentation connected to the controller. A high enough sampling rate, measurement precision, and measurement accuracy are required to achieve adequate control performance. A problem with the Derivative term is that small amounts of measurement or process noise can cause large amounts of change in the output. It is often helpful to filter the measurements with a low-pass filter in order to remove higher- frequency noise components. However, low- pass filtering and derivative control can cancel each other out, so reducing noise by instrumentation means is a much better choice. Alternatively, the differential band can be turned off in many systems with little loss of control. This is equivalent to using the PID controller as a PI Controller a APPLICATIONS AUTOMATIC CONTROL AUTOMATIC CONTROL
➲ To automate temperature control with a PID
controller, the ff are required; Install an electronic temperature measurement device Automate the valve by adding an actuator so it can be driven electronically Install a controller and connect it to the temperature measurement device and automated control valve MANUAL CONTROL ➲ Without PID controller, manual control of water temperature is a tedious process.
➲ For example, to keep a constant
temperature of water discharged from an industrial gas-fired heater, an operator has to watch a temperature gauge and adjust a fuel valve accordingly as shown. If the water temperature becomes too high, the operator has to close the gas valve just enough to bring the temperature back to the desired value. If the water gets too cold, he has to open the gas valve. APPLICATIONS
➲ PID are used in most automatic process
control applications in industry today to regulate flow, temperature, pressure, level, and many other industrial process variables. PID control examples