The goal of this project is to develop a fully functional and controllable automated system which is able to control and maintain the stability of the ambient temperature of a room. Similar systems are usually found in industry where i. e. maintenance of a storage room temperature is needed. The simulation was done by using Schneider Electric Zelio Soft 2 software. The particular model used was Zelio PLC Schneider SR2 B121 BD (24 V DC) with analog inputs.
Pushbutton and Selector switch are used from discrete inputs which are assigned as ON/OFF Switch and Mode Selection Switch respectively. Two analog inputs are also used which are assigned as Ambient temperature and Setpoint. On the output side of the PLC a heater and a fan are used to simulate the entire process. Using software, Function Block Diagrams (FBD) are programmed to control the system. 2 Overview About PLC (Programmable Logic Controller)
In general, a PLC is an industrialized computer that includes the hardware and software required to automatically control production equipment, machinery, processes, and other types of mechanical, electrical, and electronic devices typically found in industry. On the other words a PLC is the key element behind today‘s industrial automation. The PLC is mostly recognized as being introduced by Bradford Associates in nineteen sixty eight. Because it is programmable, the PLC also allows quicker changes to the equipment‘s control behavior. What to the individual words in PLC mean?
2.1 INTRODUCTION Control engineering has evolved over time. In the past humans were the main method for controlling a system. More recently electricity has been used for control and early electrical control was based on relays. These relays allow power to be switched on and off without a mechanical switch. It is common to use relays to make simple logical control decisions. The development of low ...
It may make more sense to take the words in reverse order. Controller is the key word in programmable logic controller. The PLC monitors various conditions and based on these condition determine an outcome. In other words it has ability to control devices wired to its output terminals based on the statute of the devices wired to its input terminals Logic is how we treat the various conditions we monitored which determines our final outcome. The decisions are based on logical rules that we teach the PLC by way of its programming software.
Programmable – The PLC is taught rules to how it should use the input condition to create an outcome though it’s programming software. Being programmable makes it versatile, so if needs or conditions changes, the PLC can be reprogrammed to meet these changes. It also includes the flexibility to reprogram its decision making behavior trough the software as often as needed. PLC hardware and software allows it to monitor the status of incoming events and control the outcomes. Aside from their primary use in automating factories and processes PLC are also used in simple applications such as elevators, car washes, traffic lights.
More complex PLC application includes water plants manufactories, assembly lines, machinery and bottling lines etc. 3 Internal structure of PLC Input devices: ? ? ? ? ? ? ? ? ? ? Pushbuttons Limit switches Level switches Photoelectric sensors Proximity sensors Motor starter contacts Relay contacts Thumbwheel switches 120/230 VAC 24 VDC 4 Output devices: ? ? ? ? ? ? ? ? ? ? ? Valves Motor starters Solenoids Control relays Alarms Lights Fans Horns Relays Triac Transistor/MOSFET PLC Advantages ? ? ? ? ? ? ?
Eliminates much of the hard wiring, it can be observed visually Safe Increased Reliability (very fast) More Flexibility (can be easily upgrade or modified PLC with some extension or update software ) Lower Costs (then some other industrial devices) Communications Capability (can communicate with other controllers or computer equipment) Faster Response/Operation Time Disadvantages ? PLCs are not very good at handling large amount of data, or complex data ? Difficulty in finding errors; requiring skillful work force 5 Overview About temperature regulation
Process control systems serve two different purposes. Generally the first of these purposes is to effect a change in a certain output variable, commonly encountered in the startup of a process. The second of these is to regulate or hold an output variable constant despite any changes in an input variable, which usually cannot be easily managed . In order to discuss process control, in detail it ...
Temperature control in manufacturing is an essential part of proper product formation. If the temperature slips above or below the ideal range needed for a particular stage in a manufacturing process, the results can be harmful i. e. improperly adhered coatings, a weakened base material, or an overall compromised component. So, it becomes increasingly important that the manufacturer not only determine the proper temperature for each stage, but also monitor the temperature inside the machine and receive appropriate feedback.
An on/off temperature control is the least expensive of the control types, and also the most simple in terms of how it works. The control is either on or off – if the temperature drops below a certain point, the control signals to the machine to turn raise the temperature. Likewise, if a temperature goes above a certain point, the control is triggered to tell the machine to lower the temperature. A common example of on/off systems is a household thermostat. When the temperature drops below a certain point, the controller triggers the heater to raise the temperature back to the programmed value.
With air-conditioning it works the other way: if the temperature rises past a certain point, the controller triggers the air-conditioner, dropping the temperature back to the programmed norm. On/off controls are often used in processes where the temperature change is very slow, and precise control of temperature isn’t necessary. 6 Goal As we earlier said, the goal of this project is to develop a fully functional and controllable automated system which is able to control and maintain the stability of the ambient temperature of a room. Scope Understand what is the goal in this project, and get the main idea about how to successfully implement the system ? Program a Function Block Diagram (FBD) to control the ambient temperature of a room. 7 Hardware ROOM TEMPERATURE REGULATION Specifications: The ambient temperature of a room is controlled in the heat mode by a heater and a fan, and in the chill mode only by the fan. A temperature sensor, via a converter, provides a 0-10V signal. A switch is used to deactivate temperature regulation. Screen display: The heat or chill mode is displayed The ambient temperature and setpoint are displayed.
... 18 4.2 PIN DIAGRAM: [pic] Fig:4.2.1 Pin diagram of ULN2003 Features: • No. of pins:16 • Temperature, Operating Range:-20°C ... 9 SOFTWARE 36 9.1 Software: 1. Program for gate control: #include void MSDelay (unsigned int ... loads including solenoids, relays DC motors; LED displays filament lamps, thermal print heads and high ... pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally ...
A trigger function is provided to set up regulation that takes into account a hysteresis of +2°C from start to stop and –3°C from stop to start. Description of the inputs/outputs: INPUTS: OUTPUTS: I1 On/Off switch Q1 Heater I2 Mode selection Q4 Fan IB Ambient temperature (analog input) IC Setpoint (analog input) The temperature is supplied by a sensor with output voltage of 0 to 10 V. Model Required: Zelio Logic with analog inputs. SR2 B121 BD (24 V DC) or SR2 B121 JD (12 V DC) for example. 8 Program Description: Input I1 =0 : regulation is off. Display example: *********** OFF *********** 0017. 2 InputI1 =1 : Regulation is on.
Display example: heat mode. 0020. 0 (setpoint display) 0017. 2 (temperature display) Hysteresis: The ambient temperature of room is controlled by the heater and a fan. The heater is standard commercial unit which operates on 220 VAC and it is switched by relay output Q1. The fan is a standard brushless motor fan which also operates on 220VAC and it is switched by relay output Q4. On the input side we have two switches which are used for selection of working modes, as well as to turn the system on or off. Sensing is done by the analog temperature sensor which provides signal ranging from 0 to 10 V with 255 bits of resolution.
For the setpoint analog input we use a potentiometer which enables the user to set the reference value of temperature. System has a hysteresis of +2 and -3 degrees of C regarding setpoint value. 9 Software Zelio Soft 2 is a comprehensive multilingual application designed to help us program the Zelio Logic smart relays. There are eight module categories, each displaying a picture and a full description of the characteristics such as power supply, discreet input/output, clock, language, screen keyboard, and reference, which makes them very easy to identify.
This program offers a simple way to configure the modules that are written in Ladder Diagram, Function Block Diagram, or both. When programming, we can set a wide range of parameters dealing with counters, winter/summer functions, timers, auxiliary relays, fast counters. We can also set the date format, time zone, and so on. In case of an error alarm, we can define the type of message that will be displayed, when to send a message and who will receive it via telephone or e-mail. We can also enter one or more users that can send control commands.
Analog-digital hybrid computers There is an intermediate device, a 'hybrid' computer, in which an analog output is converted into digits. The information then can be sent into a standard digital computer for further computation. Because of their ease of use and because of technological breakthroughs in digital computers in the early 70s, the analog-digital hybrids were replacing the analog-only ...
Both the user interface and the simulation languages can be switched into English, Spanish, German, Italian, or French. This program can be downloaded and used free of charge. Start window in Zelio Soft 10 Selection window which allows user to choose which module he wants to work with 11 There are two possible ways a user can write a program in Zelio Soft : ? ? Ladder logic diagram Function block diagram A basic example of Ladder logic diagram 12 A basic example of Function block diagram 13 Conclusion This project has been a very useful experience, because we learned plenty of concepts regarding automated control systems.