Continuous controllers with conmutated output
In order to work with continuous controllers with an analogue output, triggers with their corresponding inputs are necessary. Some controllers make a continuous regulation by means of a command or control contact, while varying the time of activation of a contact in fixed cycle. Therefore, the contact of control of these controllers is closed permanently with the maximum influence of the regulated magnitude. Following the example of the temperature control, the heating would be warming up to the maximum. Nevertheless, if you wish only half of this temperature, the contact of control of the controller will ignite only 50% of the time. This type of controllers can be used only with slow alterations of the regulated magnitudes, because the relays have a frequency of limited commutation.
Continuous controllers
We also have the continuous controllers which can receive many values almost continuously. The analogue output of the controllers regulates the activator or trigger. The trigger is an element of the regulation field that influences the regulated magnitude (i.e. the temperature in a heating). Through the output, these controllers control the consistency with which they will influence the regulated magnitude. If the controller gives an output with the maximum value, the heating will render to the maximum. On the contrary, if the minimum value occurs like an output, the heating will not even ignite. The possibility “of dosing” the heating capacity allows the continuous controllers a fast and precise adjustment of the magnitude regulated in relation to the set-point. Nevertheless, it is important that the controllers calculate the “dose accurately”. As output for such measurements the controllers measure the available variation of the regulated magnitude of reference value. The reaction to this variation can be, for example, proportional, but as this is technically not optimal an integral or differential part is additionally calculated. The necessary parameters must be detected for the corresponding field of control and they must be kept in the controller's internal memory. In addition, modern PID controllers offer other functions that independently detect the optimal parameters.
Discontinuous controllers Controllers are divided in different types: discontinuous controllers and continuous controllers. The discontinuous controllers have a simple property of commutation. When a limit value is reached, a relay is activated or deactivated. Because the way of working is in interrupted form, these types of regulators are denominated discontinuous controllers. The discontinuous controllers can be final switches or a bimetal. The controllers of this type are the simplest controllers. They are emphasized by its robustness and its excellent relation quality price. Due to their economic price the discontinuous controllers are acquired by companies with a low budget. The discontinuous controllers are different from the controllers of two points and controllers of three points. The controllers of two points are characterized by the switch ON/OFF commutator. They can be controllers of pH in the residual water sector where they require verifying continuously the water tanks. If the controllers detects that the residual waters are too acid, that is to say, the pH value is below 4, in such case the controllers would connect a pump to add an alkaline solution to neutralize the water. Controllers verify that the residual waters are again in the normal values and it deactivates the pump. The controllers of three points have a system of switch ON, OFF, ON. This is very advantageous in the sector of the air conditioning. Controllers of temperature measure the environmental temperature. In case the temperature falls below a limit value, for example 19 ºC, the controller switches on the heating in the offices to assure pleasant working conditions. And when during summer, the temperature is over 24 ºC, the controller can, by means of a second relay, switch on the air conditioning and lower the blinds, controlling a temperature previously predetermined.
Timer and function ramp controllers Some models of the controllers offer a timer and the ramp function. These functions allow the controllers reach different set-point values in a predetermined sequence. Also, it is possible to fix the speed with which the controllers must change the regulated magnitude. This allows the controllers automate processes without the necessity to manipulate the controllers.
Terms and definitions in the regulation and control system and instruments of regulation used.
Specific or predefined value: standard value or reference value
Regular value: present value or magnitude of control
Regulation output: Magnitude of reference
Control element: Trigger
Regulated body: Field of regulation
Structure of regulation: It indicates how the reference instruments exert an influence on the magnitudes of control. It is defined by the way of action and the type of control systems. Examples of it are: 2 point controllers, 3 point controllers, continuous controllers, cascade controllers or multizone controllers.
Behavior of the regulation: It is the form in which the controllers tend to influence in the physical magnitudes. These are the most common controllers with switch on/off commutator, PID regulators and adjustable controllers.
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