Chapter 15 The PID function of K200S MASTER-K
15-6
15.2.3 Derivative operation (D action)
1) When a deviation occurs due to alteration of SV or external disturbances, D action
restrains the changes of the deviation by producing MV which is proportional with the change
velocity (a velocity whose deviation changes at a constant interval) in order to eliminate the
deviation.
- D action gives quick response to control action and has an effect to reduce swiftly the
deviation by applying a large control action (in the direction that the deviation will be
eliminated) at the earlier time that the deviation occurs.
- D action can prevent the large changes of control object due to external conditions.
2) The period of time from when the deviation has occurred to when the MV of D action
become the MV of P action is called derivative time and represented as Kd.
3) The D action when a constant deviation occurs is shown as Fig. 15.7.
Figure 15.7 Derivative action with a constant deviation
4) The expression of D action is as following ;
dE
TdKpMV ×=
5) Derivative action is used only in PID action in which P and I actions combine with D
action.
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