AUTOMATIC LIQUID LEVEL MONITORING & CONTROLLING USING PLC
Jyoti M Shettar & Ekta Maini
Assistant Professors, IT department, DSCE, Bangalore
ABSTRACT:
The goal of this project is to design a prototype module of PLC to meet the industrial requirements. Basically the system consists of 3 level tanks and one main storage tank to control the levels according to the PLC programming sequencer and tank levels are sensed by a level sensor called float switch. If any of the tank level goes down to a minimum level of set point the PLC automatically detects the level of the tank and switch ON the motor to adjust the maximum levels in order to maintain the desired level in all the 3 tanks. Once the level reaches the maximum levels of all the 3 tanks the PLC automatically turn OFF the motor . All the control operations, levels of each tank, status of the motor and solenoid control valve positions are indicated by the LED’s in the front panel of the automated level monitoring and control system.
- INTRODUCTION
The monitoring and control of liquid level is a common requirement in a broad range of industrial, processing and plant management systems. In many situations, it is only necessary to ensure that a liquid does not overflow a container or that the liquid level does not drop below a prescribed minimum level. Applications include boiler low level cut-off protection and feed water level control, pump interlock and control, food and cooking equipment, dairy monitoring systems, steam cookers, water dispensing systems and moisture (leakage) detection. There are a wide range of measuring techniques available, including ultrasonic, hydrostatic pressure monitoring, optical and simple conductive measurement. The type of measurement is often dictated by the type of fluid being monitored. Highly caustic or corrosive materials often preclude any direct contact with the liquid, necessitating indirect measurement using ultrasonic’s, radiometric or other non contact techniques. Control is the key function of automatic control that does not rely on human interference. To fulfill a task, the controlled system variables are sensed and fed back, generating control signals which are applied to the system. Control is a physical concept as the results of control are usually seen in changes in some physical variables. Feedback control was used in early human history as humans learned to make tools and change their environment. One example is the float regulator mechanism used to control the liquid flow rate in a water clock or the liquid level in a liquid tank.
- BLOCK DIAGRAM OF PROPOSED SYSTEM
Fig.1. Block diagram of proposed system
- SYSTEM COMPONENTS
Programmable Logic Controller (ABB PLC)
24V DC Solenoid Control Valves
5/12V DC Submersible Pump
Level sensors (Float switches)
The PLC or programmable logic controller can be classified as a solid state member of the computer family. A programmable logic controller is an industrial computer in which control devices such as limit switches, push buttons. Proximity or photo electric sensors, float switches, provide incoming control signals into the unit called an input.Inputs interact with instructions specified in the user ladder program, which tells the PLC how to react to the incoming signals. The user program also directs the PLC on how to control field devices like motor starters, pilot lights, solenoids. A signal going out of the PLC to control a field device is called an output.PLCs have been gaining popularity on the factory floor and will probably remain predominant for some time to come. Reliable components make these likely to operate for years before failure.
A solenoid valve is a combination of two basic functional units:
• A solenoid (electromagnet) with its core
• A valve body containing one or more orifices
Flow through an orifice is shut off or allowed by the movement of the core when the solenoid is energized or de-energized. Valves have a solenoid mounted directly on the valve body. The core is enclosed in a sealed tube, providing a compact, leak tight assembly.
Fig.2. Solenoid Valve
The magnetic float switches are made of plastic or stainless steel have build-in magnets and are used to magnetically actuate a reed switch(es) in liquid level sensors. Float-type sensors can be designed so that a shield protects the float itself from turbulence and wave motion. Float sensors operate well in a wide variety of liquids, including corrosives. When used for organic solvents, however, one will need to verify that these liquids are chemically compatible with the materials used to construct the sensor.
A special application of float type sensors is the determination of interface level in oil-water separation systems. Another special application of a float switch is the installation of temperature or pressure sensors to create a multi-parameter sensor. Magnetic float switches are popular for simplicity, dependability and low cost.
Fig.3. Magnetic float sensor
- FLOW CHART
Flowchart of the proposed system
- LADDER DIAGRAM FOR PROPOSED SYSTEM
Fig.4. Ladder logic program for the liquid level monitoring and control system
- RESULTS & CONCLUSION
Table.1.Status Table for the minimum and maximum liquid levels of 3 tanks in the front panel
Many types of tank gauging systems have adequate reliability in liquid measurement applications, a range of level control systems and methods are used in industry. Systems may be based on the use of floats or even more sophisticated technology. A modulating level control system consists of a float sensor and appropriate controller, which provides a modulating output signal, typically 4-20mA. This output signal may be used to affect a variety of devices including:
- Modulating a control valve
- Operating a variable speed pump drive.
- Because the float and controller only provide a signal to which other devicesrespond, rather than providing the power to operate a device, there is no limit on the size of the application.
- Steady control of level within the tank.
Many different types of control systems are used in industry, covering a wide range of processes. Some processes will be concerned with media other than liquids, such as dry powders and chemical feedstock.
A float rises and falls according to the change in liquid level and operates switches at predetermined points in the range. Hence many systems are available to serve this wide range of applications.
- REFERENCES
1.Bryan, L.A. and Bryan, E.A., Programmable Controllers: Theory and Implementation, Industrial Text Co., 1988.
2.Swainston, F., A Systems Approach to Programmable Controllers, Delmer Publishers Inc., 1992.
3.Batten, G.L., Programmable Controllers: Hardware, Software and Applications, Second Edition, McGraw-Hill, 1994.
4.Bolton, w., Programmable Logic Controllers: An Introduction, Butterworth-Heinemann, 1997.
5.Filter, R., Leinonen, G., “Programmable Controllers and Designing Sequential Logic”, Saunders College Publishing, 1992.
6.Kirckof, G., Cascading Logic; A Machine Control Methodology for Programmable Logic Controllers, The instrumentation, Systems, and Automation Society, 2003.
7.Boucher, T.O., “Computer Automation in Manufacturing; An introduction”, Chapman and Hall, 1996.
8.Authors
i) Jyoti. Shettar
Asst.Prof, IT dept, DSCE
Bangalore
Email:
ii)Ekta Maini
Asst.Prof, IT dept, DSCE
Bangalore
Email: