Control elements
CLASSIFICATION
PRIMARY ELEMENTS:
They are the ones that are in contact with the variable and use or absorb energy of the controlled medium to give to the measurement system an indication in response to the variation of the controlled variable.
The primary elements constitute a set of important devices for any instrument. Its function is to initially detect the value of a variable during the operating process, so they must maintain a continuous contact with the various properties that may be subject to change in the system (pressure, force, position, electrical measurement, among others), all this by means of the use or absorption of the energy of the controlled medium, to give the measuring medium an indication in response to the variation of the controlled variable.
Also, they are those who are willing to transmit any transformation of the medium, being the first element in a control loop which measures the process variable, its effect produced can be a change of pressure, force, position, electrical measurement, between Other.
Pressure sensor: The pressure sensors are devices that transform the physical magnitude of pressure per unit of surface into a normalized signal, normally 4... 20 MA. The measurement ranges are very wide, from a few thousandths of bar to the thousands of bar. Pressure sensors without signal amplification are also called transducers.
Level Sensor: is an electronic device that measures the height of the material, usually liquid, inside a tank or other container.
Temperature Sensor: Used to detect temperature variations. They are constructed from materials whose electrical resistance varies depending on the temperature.
Contact Sensor: Used to detect the end of the travel or the limit position of mechanical components. For example: Knowing when a door or window that opens automatically is already completely open and therefore the motor that drives them must stop.
Optical sensor: Detects the presence of a person or an object that interrupts the beam of light that reaches the sensor.
Humidity Sensor: They are based on that water is not an insulating material like air but has an electrical conductivity; For this reason, the low voltage regulation prohibits the presence of sockets near the bath, as we saw in the previous issue.
Magnetic Sensor: Detects magnetic fields that cause magnets or electrical currents. The main is the Llamadointerruptor Reed; It consists of a pair of metallic sheets of ferromagnetic materials tucked inside a capsule that are attracted in the presence of a magnetic field, closing the circuit.
Infrared Sensor: There are diodes capable of emitting infrared light and transistors sensitive to this type of waves and which therefore detect the emissions of the diodes. This is the basis for the operation of remote controls; The control contains infrared emitting diodes that are received by the photo transistors of the device.
SECUNDARY ELEMENTS:
They capture the signal produced by the primary element and transform it into output that can be captured by another instrument locally or remotely. It detects the error signal, which is usually at a low power level and amplifies to a level high enough.
The device that has the intelligent part of a Process control system is the controller; It contains the functions of memory, mathematical and logical operations, decisions and in general the control algorithm.
Transmitters:
Consist of being instruments that interpret physical phenomena, which translate into standard signals of engineering. The transmitters are devices that are connected to the primary element in some cases it is integrated to the transducer, it produces the signal for the transmission.
In the case of the proposal, they will be implemented with the purpose of sending the data collected by the sensors to the controllers in order that they execute their control action according to the value obtained and programming inserted, achieved in this way, that everything It works the way it was conceived. Likewise, the obtained values will be sent to the control center with the purpose of obtaining a report of the statutes of the processes and level of spices of the silos.
Drivers:
Are devices that regulate the controlled variable (pressure, level, temperature, etc.) comparing with a default value or set point and adjusting the output according to the difference or result of the comparison in order to exert Corrective action according to the deviation.
The controlled variable can be directly received as local controllers, or indirectly in the form of a pneumatic, electronic or digital signal from a transmitter.
Is responsible for deciding the type of action on the final control element. The controller has two essential functions:
• Compare the measured variable with the desired reference (point of Operation or Set point), to determine the error that exists between them.
• Send a signal to the final control element in order to modify its action in the appropriate sense to reduce the error.
Pressure transmitter
Flow transmitter
Pressure Controller
Flow Controller
Charge controller
TERTIARY ELEMENTS:
This is the part of the circuit that provides the final control element.
Is a device that converts a control signal into a mechanical action.
Pneumatic actuators are linked to on-off control nodes.
The final control element is one that finally modifies some feature of the process as ordered by the controller. Depending on the type of process and the objectives, you have a variety of these elements. From devices that receive control signals of the discrete type to others that act by regulating the variable of interest within a certain range such as the flow of a fluid through a control valve, the speed of an engine by means of a veil variator The temperature of an electric oven using a heating element.
A control valve is the most Comunmnete control end element used in the industry. This device varies the flow of material or energy into a process by adjusting an opening through which the material flows. It is therefore a variable orifice in the line.
Electric motors
Valves
Centrífugaz Pumps
Switches
Fans
