Damping

Damping

          When torque is applied in a system in a direction opposite to its motion, it is known as Damping. In case of coulomb damping, the opposition is constant and, thus there will be a constant difference between the input and the output under steady conditions. In the viscous damping provided by dashpot, the opposition is proportional to the relative velocity. As the relative velocity is zero in the steady state, the damping is also zero.

Overall Transfer Function

Overall Transfer Function

          In the previous topic, we have discussed the transfer function of a block. In this we are going to know the Overall transfer function of a control system. A control system actually consists of several such blocks which are connected in series. The overall transfer function of the series is the product of the individual transfer functions. Consider a block diagram of any control system represented by the three blocks as shown in Fig., 

Fig. Overall transfer function.

          Thus, if  are individual transfer functions of three blocks in series, then th overall transfer function of the system is given as 

Where       K = Constant representing the overall amplification or gain, and 

                  G(D) = Some function of the operator D.

Note: The above equation only true if there is no interaction between the blocks, that is the output from one block is not affected by its connection to the subsequent blocks.

Open-Loop Transfer Function

Open-Loop Transfer Function

          The open loop transfer function is defined as the overall transfer function of the forward path elements. Consider an open loop control system consisting of several elements having individual transfer function such F₁(D), F₂(D), F₃ (D)  as shown on in Fig.,  

Fig. Open loop control system.

 Thus

                                    = F1 (D ) X F2 (D ) X F3 (D ) = KG (D)

The simplified block diagram of the open loop transfer function is shown in Fig.,

Fig. Simplified open loop control system.