Programable Logic Controller Basics Explained - automation engineering

Almost all commercial buildings and industrial facilities depend on the

automation

of their mechanical and electrical systems. This trend will only increase, especially as larger, smarter and more complex systems and buildings are constantly being built, so how do we control these systems and what devices are used to achieve that, that is what we will cover in this video sponsored by telecontrols . Telecontrols is one of the leading manufacturers in the

automation

industry since 1963. Its technology is compatible with all PLC HMIs and

controller

s on the market, reducing PLC programming time. and save valuable storage by taking care of smaller automation tasks directly.

Click the link in the video description below to learn how Teles products can make the most of your plc application. You can contact them in sales at telecontrols.com or even via linkedin plc stands for Programmable Logic Controller There are many variations but they usually look like this. A programmable

logic

controller

is basically a small computer that can perform pre-programmed outputs based on inputs and a set of specific rules that are used in commercial and industrial applications to control. systems with minimal and sometimes even no manual intervention, the operation can be a simple on-off control based on the state of the input or a more sophisticated response based on the sequence of calculations and

logic

before the Control of the PLCs will be carried out through banks of relays, each relay controlled in a dedicated manner.

Inputs and outputs based on hard-wired relays would control other relays to form logic controllers, for example with a simple gate and only when two inputs are energized, this one and this one the relay output energizes these inputs could be sensors or could be outputs of other relays to change operation, the physical wiring had to be changed, so the physical connections had to be modified if a different response was ever required. These old relay banks were large and very complex. This is an example of an elevator relay bank and This is the relay bank of an old electrical substation, as you can imagine, it will not be easy to change them and finding faults can be difficult and time consuming with the invention of electronics. solid state and microchips, the command logic part of the relay banks could be replaced with software logic, so PLCs quickly took over.

PLCs vary widely in their application, but they all monitor their inputs, make a decision based on a stored set of rules, and from them then issue commands to automate a process we often encounter. Relays used in combination with PLC Relays can directly handle automation tasks and communicate with the PLC. This will reduce the amount of programming required on the PLC and also free up storage space. PLCs are widely used, for example, when you check a suitcase at the airport, the bag receives a barcode and enters the conveyor belt. A plc scans the barcode and, based on a set of rules, decides whether the bag is diverted to the domestic or international route.

The next plc scans the barcode and decides in which city the bag is located. it needs to be diverted to the next plc decides which door it also needs to be diverted to and if all this goes as planned then the bag will reach the correct door first we have the input modules of the field sensors these are the physical connections between the outside world and the plc, these can be digital inputs, such as simple on and off switches, biometallic temperature strips, presence or motion sensors or even a float switch, these digital inputs can only provide information about whether something is on or off and nothing in between for that. we would need an analog input, for example a simple control knob that varies from zero to one hundred percent.

This will go through a voltage transformer to give zero volts at zero percent and ten volts at one hundred percent. The plc can scale the input to match the required sensitivity for very precise output control. You could also convert voltage to current using resistors and Ohm's law. The amount of current usually measured in milliamps tells the PLC whether something is operating between on and off. These inputs could be, for example, a thermocouple or a resistor. temperature detector, it could be a pressure sensor or perhaps a voltage meter, these voltages or currents are converted into an equivalent digital number that the CPU can understand.

We'll see it a little later in this video. The input modules will perform four main tasks. sense when a signal is received convert the signal voltage into the correct signal for the CPU isolate the PLC from fluctuations in the input voltage or current signal and send the corrected signal to the CPU the CPU or central processing unit is the brain of the operation contains the program or software that decides what outputs are required by applying rules to the input signals the CPU usually consists of a microprocessor that performs the work based on the input value and the logic of the program a memory chip to store the program this will also store the output history, any faults or alarms etc, then we also have other ICs, which can be things like modbus and lan connections that allow us to communicate remotely with reprogramming or even monitor the device , then there are the output modules or the field output. devices, this provides the signal to the device we are controlling, for example, a simple indicator light, a solenoid valve, a motor starter, a variable frequency drive, etc., there are some other parts, such as a battery, to keep the plc in case of a power outage. there may be a small screen for a user interface that allows for some configuration; there will need to be a clock and calendar to operate a device at the correct time and there will also need to be a power supply to provide the low voltage used by the CPU as well as the input and output modules, by the way, we have We covered motor starters and solenoid valves of variable frequency drives in detail in our previous videos.

Check those links which can be found in the video description below, the basic operation of a plc is to perform a pre-programmed output depending on the input signal following a set of rules, the plc completes the following stages in its basic operation, first there is the input scan which detects the state of the inputs, then the program scan to see what is needed then it will run the program logic to actually implement what the rules state, then it must update the outputs to operate the output devices depending on program requirements, finally maintenance for self-diagnostic communications updates and scan time reporting, which is the time what is needed to complete all stages depends on sensitivity, resilience and time system processing.

Analogue inputs tend to take longer to process compared to simpler on/off digital inputs, for example a water tank may have a very fast scan time of 2 milliseconds and this prevents overfilling, but the control of room temperature can be much slower, perhaps 100 milliseconds. Let's look at an example of a simple response. We have a bimetal strip temperature sensor, a PLC and a boiler. The biometal strip bends as it heats and cools so we can use it. this to detect if the room is at the desired temperature and from this control the boiler when the room is at the correct temperature the circuit is complete and the plc receives a signal so the boiler turns off when the room temperature drops the circuit already is not complete and the plc detects its change in the input, reacts by sending an output signal to turn on the boiler.

This is very simple and we could also use a simple relay to achieve this, however a plc is better because it has a time function so we can check the time before turning on the boiler, for example the building may be empty at nights and weekends, so we don't want the boiler to turn them on. The plc is told that the room is too cold. Check the time and date to see. if it is allowed to turn on and then based on this it is decided whether to turn on or leave the boiler off, we can add additional functions and inputs, for example a motion sensor at the entrance, the thermostat tells the plc that the room is too cold, the plc will check the time to make sure you are allowed to turn on the boiler and now you can also check if the room is occupied, for example there could be a holiday not on the calendar, the building is empty, so the boiler does not need to be turned on.

In the next more sophisticated example, we have a thermistor, a plc and an actuator valve. The thermistor can provide a temperature scale instead of a simple on-off input like the biometal strip. The actuator valve can be opened at any point between zero and one hundred percent to control the amount of hot water that is provided to heat the room, for this we would use a pid control loop which stands for proportional and derivative integral control. We won't go into too much detail about the pids, but essentially this will control the position of the valve to ensure that it only opens enough to accommodate the difference between the desired room temperature and the actual room temperature, for example if the room temperature dropped very slightly, we don't want the heating valve to instantly open to 100 because the room will also heat up. rapidly and this will exceed the desired temperature at this point, then it will turn off instantly and the cycle will repeat.

Instead, we want the valve to open gradually in proportion to demand, so that if there is a small temperature difference, the valve slowly opens a little. If there is a large temperature difference, the valve opens faster and faster, then slows down as it approaches the desired temperature until the valve finds the perfect position to maintain the desired room temperature. Let's look at a more complex example in many commercial buildings: the heating or cooling system. will use a control strategy known as an optimizer, which learns over a period of time how quickly the building heats and cools and then starts the heating or cooling system at the optimal time before the building is occupied, for example if the staff must arrive. to arrive and start work at 9 a.m. m., the heating system knows to turn on at 7 a.m. m.

To ensure that all rooms are at the correct temperature, let's say this system has a plc with optimizer software installed, this controls an actuator valve for the heating system, this system also has two pumps that are set to run and standby. , so only one pump works at a time. The PLC will decide which pump to turn on based on the one with the fewest previous operating hours. The PLC will monitor a flow sensor to detect if the pump turns on when told to do so if the pump does not turn on the plc receives an alarm and will cut off the power then tells the other pump to start however , before the heating system and the pump turn on the The plc will check with the clock whether the heating is turned on today and, if so, what time will the building be occupied?

The clock says yes, the scheduled occupancy time is 9am, the plc then checks the current room temperature and calculates the difference between this. and the desired temperature, then check the outside temperature to calculate how long it will take to heat the building because on a very cold day there will be more heat loss and therefore this will take longer. From there the plc calculates what time it needs to turn on the heating system so that the building is at the desired temperature and ready for 9am. m. By the way, we covered service and standby pumps and relays in our previous video.

Please check that the links can be found in the video description below. There are many advantages of PLCs, but some of the main ones are: The control software is stored locally, so in the event of a failure in the building's energy management system, the PLC can continue to operate. The connections between the inputs and outputs of the PLC are made by software and not by many physical cables. PLC installations are smaller than wired relay banks but can still use relays when necessary. PLCs are much easier to reprogram. Troubleshooting is easier and faster You can load the same program on multiple PLC units to save time It also expands the inputs and outputs with morecards.

Okay, that's all for this video, but to continue learning about controls and electrical

engineering

, watch one of the videos on screen now and I'll see you there for the next lesson. Don't forget to follow us. us on facebook twitter instagram linkedin as well as in

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