Question

I have some question about PID applied Cruise Control within Simulink.

First of all, am a bit confused about the the property of PID applied feedback system. According to the following figure, the use of a PID controller is to minimize or eliminate the difference between SP and PV. However, since a transfer function has been applied to the loop which is the process block in the following diagram then how the difference could be possibly erased?   

  

Here is the classic block diagram of a process under PID Control. Disturbances(s) Controller Output Process Variable (PV) Setpoint (Sp)PID CONTROLLER PROCESS Measured Process Variable SENSOR What' s going on this diagram? The Setpoint (SP) is the value that we want the process to be. For example, the temperature control system in our house may have a SP of 22°C. This means that "we want the heating and cooling process in our house to achieve a steady temperature of as close to 22°C as possible" The PID controller looks at the setpoint and compares it with the actual value of the Process Variable (PV). Back in our house, the box of electronics that is the PID controller in our Heating and Cooling system looks at the value of the temperature sensor in the room and sees how close it is to 22°C.

For example, in the following diagram, i have produced a simple no control open loop diagram which will transfer the input force to the certain output velocity. As a result, in this case, if i wish to regulate the output velocity then how am suppose to add in a PID controller to make it a closed loop controlled system? If following the statement in figure 1 then no matter where i place the PID controller, it will always be the comparison between the input force and the output velocity which has got no physical meaning.  

Thus, as my questions:

1. whats the difference between the stated example in diagram 1 and 2? why one example has two equivalent physical parameters but one has not?

2. where should i add in the PID controller in my second example so that output velocity block could display the regulated velocity and why?  

Answer 1

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