Automatic regulators are different both in terms of the principle of the device and the algorithm of action. They have one thing in common - they all implement feedback.
The most common type is on-off. This is the simplest and cheapest device for maintaining the desired parameter in a given range. There are many examples of such systems; they are used in both industrial and household appliances. An iron, an electric heater - a convector, an AGV and even a toilet bowl - these are the devices that use the simplest two-position scheme, the principle of which is that the regulatory body (RO) is either in one extreme position or in another. The disadvantage of this method of controlling the output parameter is the low control accuracy.
Proportional controllers are more complex. They generate a signal for the position of the regulator, depending on how much the value of the controlled parameter has increased or decreased. There are no longer two positions for the RO, it can be located at any intermediate points. Principle of operation: the more the output parameter deviates from the set value, the more the position of the adjustable body changes. The disadvantage is the presence of staticerrors, that is, a stable deviation from the set value of the output parameter.
To eliminate this error, integral regulation is used. As a result, proportional-integral (PI) controllers appeared. Their disadvantage was the inability to take into account the inertia of the regulated system, its delay in relation to the control action. By the time the regulator reacts to the disturbance of the system, it is quite possible that a completely opposite effect is needed, and the negative feedback can turn into positive, which is highly undesirable.
The most perfect is the PID controller. It takes into account the differential component of the accelerating characteristic of the controlled parameter, that is, the rate of its change as a result of a step-like change in the position of the RO. Tuning the PID controller is more complicated, it is preceded by taking the acceleration characteristic, determining such object parameters as the delay time and time constant. In addition, all three components are configured. The PID controller provides effective stabilization of the output parameter without static error. At the same time, it excludes parasitic generation.
PID controller can be made on different element base. If the basis of its circuit is a microprocessor, it is most often called a controller. The accuracy of maintaining the parameter is calculated according to the principle of reasonable sufficiency.
It happens that the technological requirements for maintaining someof the parameters are so rigid that only the PID controller can be used. An example is microbiological production, in which the thermal regime determines the quality of the product. In this case, the PID temperature controller will maintain the microclimate with an accuracy of 0.1 degrees or less, if, of course, the sensors are correctly mounted and the settings are calculated.
