Manually Controlled Closed Loop System

Example of a Manually Controlled Closed Loop System: 

As an example of a manually operated closed loop system we take the case of driving of an automobile. The block diagram of the closed loop system is shown in Figure.
Manually Controlled Closed Loop System
The route, speed and acceleration are determined and are controlled by the driver. The driver observes traffic, running details on road. Accordingly he operates the accelerator, breaks, clutch, gears, steering wheel, lights etc. If the driver wants to maintain a speed of say 50 km/h, which is the desired output, he will apply that force on the accelerator pedal required to maintain the speed constant.

He also holds the accelerator pedal constantly with the same pressure. The speed of the vehicle will be constant as long as there is no gradient or other problem of traffic. Normally no vehicle on road could go at a constant speed. The road conditions, traffic on road will have their effects on the speed of a moving vehicle.

The speed of the vehicle is indicated by the speedometer. The driver views the speed in it and regulates it. He mentally calculates the speed shown by the speedometer with the desired speed. So he will regulate the speed by changing the pressure on the accelerator pedal. This is done using the foot [muscular power]. The sequence of all these operations can be represented in a diagram. This is called a closed loop system of the manually controlled type. The instantaneous speed of the vehicle is observed by the driver who reacts suitably and maintains the desired speed. Hence the driver performs the important role in this control loop.

Disadvantages of Manually Controlled System:

1. In a complex fast acting system the system response may be very rapid. Under such conditions the operator may fail to operate or control the system.
2. The operator must possess extremely high skills.
3. Failures are expected due to human errors in spite of good skills.
4. In certain applications such as in defence the systems are self destructive. No operator should be employed in such systems.
5, Elimination of human interference is economical, accurate, error free and efficient.

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