Control Systems: Types, Signals, Converters, Sensors, Actuators, Memories, and UPS
1.1.3. Control System
There are two ways to perform automatic process control: open loop and closed loop.
A) Open Loop Control
Performs the functions of output according to the instructions of entry, regardless of changes in output. The command signals are independent of the output and the system fails to recognize if an order has been properly implemented, and cannot correct the external shocks affecting the system.
B) Closed Loop Control
In closed-loop control, control signals into the system are a function of the slogans of entry and exit developments. It collects information from the output, compares it with the slogans of entry, and generates orders to correct the system state. Thus, the controller is capable of correcting external disturbances.
1.1.4. Signal Types
According to the types of signals to treat, they can be classified into digital and analog:
A) Digital
Can take values of 0 and 1, being generally (depending on the technology used) 0 zero volts and 1 five volts when we are in positive logic. Can represent only discrete values.
B) Analog
Can take any value between an individual margin. Are continuous signals that can represent any value within a certain range.
1.1.5. Signal Converters
In automated plants, both analog and digital signals are found. In general, the systems process information in digital format and show the need for analog-digital converters (A/D). After processing the information, orders may be sent to the system in analog format, therefore, we have digital-analog converters (D/A). There are converters of 8, 12, 16 bits, etc.
1.1.6. Sensors and Actuators
Sensors are elements that can transform the nature of a magnitude into another that is more easily measured by our control system, generally electrical. The current or voltage sensor is a simple pushbutton.
Similarly, all the control system wants is to act abroad to modify the current system state (turn on a light, open a door, etc.). These actions are carried out through actuators, and actuators and transducers can also be seen as responsible for transforming the nature of the output signals.
1.1.7. Memories
These control systems require components that are able to store both program instructions executing the control as temporary data that indicate the current status of the installation. This function is performed by the memories.
The memories are organized in blocks that define the length of the stored information. The basic unit of information that can be stored is a bit. These bits are grouped to use larger units of information, usually 8 bits (byte) or 16 bits (Word).
To access a memory word, we need an address line that indicates the position of the memory word you want to read or write. To address all memory locations, we have to have a number of lines m which depends on the number of words it can store. In general, with m address lines, we have 2m addressing memory locations.
Logically, the memory must have a data line depending on the number of bits to store each position n. In addition to the proper functioning of the memory, we need some control lines that allow us to control the memory and, in general, allow us to make processes of writing or reading.
The memory capacity is determined by the number of words that can be stored. In general, we can compare reports of different lengths of words expressing the memory capacity as the total number of bits that can be stored. So if an n-bit memory having 2m memory locations, the total capacity (N) in bits of memory is:
“` N = n * 2^m “`
Types of Memory
Depending on the type of access to data in the reports, they can be classified:
– Sequential – Random access or random access memory, allowing the following classification:
1. ROM (Read Only Memory). Read-only memory. You can only burn once. It is a volatile memory. 2. RAM (Read Access Memory) can be stored and read the data as often as desired. It is used for temporary data in an application. It is volatile, the information is lost if the memory is not powered. 3. EPROM (Electronically Erasable Read Only Memory Program) Like the ROM, but allows erasing and writing from memory.
1.1.8. UPS
Problems in the UPS power supply can cause loss of information in systems that use memory programmed to store the control program and the temporary data of the application.
The UPS (Uninterruptible Power Supply) is a device whose main function is to supply electricity when a fault occurs in the supply of electrical energy. They are not considered self-powered devices alternative to the electric grid because their storage capacity is limited. So you have to distinguish between a UPS and an autonomous power (generators).