Chapter 7 Usage of Various Functions
7-30
Fig. 2.6 The system response when a short integration time given
c)
Derivative operation (D action)
(a)
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 proportioned with the change velocity (a velocity whose deviation changes at
every constant interval) in order to eliminate the deviation.
4
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.
4
D action can prevent the large changes of control object due to external conditions.
(b)
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.
(c)
The D action when a constant deviation occurred is shown as Fig. 2.7.
Fig. 2-7 Derivative action with a constant deviation
