In an open loop system, a dual input into the controller logic does not depend on automatic control variable value feedback. It means the output value is predetermined and expected. Open loop control systems are simple and basic. Because there is no dependence on the system output, this control system does not need or can include feedback.
The actuator controls the process in this no-feedback control system. This system assumes that the output does not need to be measured or regulated and will work as desired. We buy a TV, use it till it breaks, and fix it.
Advantages of Open Loop Systems
Open Loop Systems have advantages over close loop systems. The system is simple because there is no feedback or correction. Installation is simpler and cheaper. Open loop systems work well for non-precision processes. Other systems take longer to commission and start up. These features have made open loop systems popular in many sectors for diverse operations.
Disadvantages of Open Loop Systems
Because they only respond to a given input and ignore a key variable, open loop control systems are sometimes less accurate and trustworthy than closed loop systems. This means that distorted input can cause sophisticated control systems to fail, especially in safety-critical environments.
2. Components of an Open Loop System
2.1. Input Device
The input device starts an open loop system. This device monitors output and compares it to fixed point. After this comparison, the input device tells the controller if the set point has been reached. Many input devices are employed, including thermometers, pressure gauges, and light sensors. Open loop systems are used when the system must only run under one condition, so the input device simply needs to check output to set point rather than alter the system.
Here, input and output devices are connected. The controller converts input device data, which the memory converts into output device positions and power. The controller synchronizes all open loop system operations.
Actuators in open loop systems include valves, motors, switches, relays, and solenoids. This system device responds to the controller. The controller continuously analyzes the system and regulates the actuator to determine if the input value is meeting expectations. Controlling open loop systems involves position or velocity control. The minor difference between the input and the output causes changes in the input values, making these systems open loop systems. If the input-output error is small, all the benefits are applicable and feasible.
2.4. Output Device
This is a typical Open Loop system using a block of flats’ heating system. Boilers heat system water. Flats’ flow and return pipes, usually beneath the stairs, contain thermostatic radiator valves (TRVs) and lockshield valves. The lockshield valve controls system water flow. The TRV stops flow when heating is off. Adjusting the TRV so that the thermostatic head senses room temperature and opens when heat is needed through the radiator maintains comfort.
What Is an Open Loop System?
An open loop system operates without feedback to assess if its output meets its purpose. A control signal is output based on input and predefined algorithms without testing for accuracy.
In an open loop system, the input device sends data to the controller. After determining the answer, the controller signals the actuator to engage the output device. Most importantly, the system does not verify that its response met expectations. It reacts mindlessly to input.
Since open loop systems have no sensors or feedback loops, they are cheap and easy to develop. They operate effectively in situations with few interruptions and rough output control. Their lack of input limits their accuracy and precision. Their faults and inability to adjust to environmental changes are also issues.
Common open-loop systems include:
Control fan speed manually. The fan does not validate its speed when you pick it.
A basic washer. It fills, agitates, drains, and spins on a timer without checking for cleanliness.
Timed traffic lights. The lights change at a set time without sensing vehicles.
Open loop systems are effective for controlling basic consumer product operations, industrial processes with few variables, and transportation systems with few variables. For precision and adaptability, a closed loop system with feedback is usually better.
Components of an Open Loop System
The input, controller, actuator, and output devices make up an open loop system. These components operate linearly to control the system.
The input device detects a process signal or condition to control. Possibly a switch, sensor, or transducer that measures temperature, pressure, flow rate, etc. The controller receives system status signals from the input device.
Open-loop controllers make decisions. The controller selects output based on input device signal. It might be a thermostat or PLC. The controller instructs the actuator to alter.
The actuator directly regulates a system element by transforming energy into motion. Valve, switch, relay, and motor are examples. The controller commands the actuator to adjust the process.
Actuator control signal results are shown on the output device. It checks if the actuator responded properly but does not tell the controller to correct. The output device could be a meter, alarm, or indication light.
Open loop systems are simple and cheap, but they lack feedback to remedy faults and disturbances. The output assumes suitable controller input and output devices and set points. To regulate complicated processes accurately and responsively, a closed loop system with feedback control is generally needed.
Open Loop Systems in Daily Life
Open loop systems are more frequent than you think. Many everyday devices and appliances use open loop control. Here are some familiar examples:
A typical example is an automatic washer. In the wash cycle, the machine fills with water, agitates and spins according to a program, empties, and typically spins again. The wash software doesn’t know if the items are clean—it just repeats the pattern. Only you can physically evaluate the load to determine if another cycle is needed.
Traffic lights are another example. The lights cycle from green to yellow to red without regard to traffic volume. Traffic studies may modify light timings, but each cycle is open loop.
Electric fans and other small equipment use open loop control. A fan stays at a speed you set until you turn it off. The fan spins at the selected speed without knowing if the room is at the correct temperature or circulation. Monitor the situation and adapt as needed.
Others open loop systems you see daily include:
- Timed automatic doors (not sensing whether someone needs to pass)
- Sprinkler systems (they cycle between zones on a schedule, not soil moisture levels)
- Open loop systems simplify our lives for many simple processes and appliances, notwithstanding their drawbacks. Learning how technology works can improve your usage of it.
Applications and Advantages of Open Loop Systems
Practical uses and benefits of open loop systems abound. They are perfect for easy operations that don’t require precise control or monitoring.
Industrial operations that involve repeated, high-volume production use it. In a bottling plant, the same steps are repeated to fill and cap bottles on an assembly line. This can be done without feedback with an open loop system with preset parameters.
Use is also prevalent in simple consumer gadgets and appliances. A programmed wash/rinse/spin cycle is used in your automated washer. An open loop system uses a timer to start each cycle. The washer lacks sensors to verify garment cleanliness!
Open loop control benefits transportation systems. Traffic lights automatically turn between red, yellow, and green at set intervals to keep traffic flowing. They run on a timer without checking for automobiles. For instance, your home electric fan blows at the speed you specify regardless of ambient temperature.
Benefits of open loop systems include:
• Easy and cost-effective implementation without sensors or feedback mechanisms. • Reliable for repetitive tasks or low accuracy.
•Easy to comprehend and fix. The fixed controls rarely change. •Fast response times since feedback is not processed before output adjustment. The device reacts instantaneously to pre-programmed commands.
Open loop systems are reliable and economical for repetitive activities, but they lack precision in complex applications. Their low cost and simplicity make them valuable in industrial and consumer settings. Choosing the correct control system requires knowing their strengths and weaknesses.
How Do Open Loop Systems Differ From Closed Loop Systems?
Control systems like open loop and closed loop work differently.
In an open loop system, the controller controls independently of output. No feedback loop exists—the system does not modify its output based on findings. The system assumes output matches expectations. An open loop system is like following a recipe—you input the components but don’t know how it will turn out until you taste it!
However, a closed loop system uses input to determine its success. Adjustments are made to remedy faults after comparing actual output to expected output. This would be like tasting the food as you cook and adjusting the recipe based on the outcomes.
Some important distinctions between the systems:
Closed Loop Open
No feedback, uses feedback
From cheap to pricey
Closed loop systems can handle changes and fix problems better than open loop systems, which are cheaper and simpler. Many real-world systems combine open and closed loop control to maximize benefits.
Here’s an introduction to open loop systems. We discussed their definition, operation, real-world examples, applications, and comparison to closed loop systems. As seen, open loop systems offer pros and cons depending on the situation. Although cheap and simple, they lack feedback, which can lead to errors. This should lay the groundwork for future learning! Remember that systems thinking applies to many fields, whatever your hobbies. Consider how feedback affects control loops and the world. An open, curious mind will lead to fresh discoveries. Try some systems yourself!