VLT ® 2900 Series Select the required gain limit. 20.00 - 999.99 ms (1000 = OFF) 100 ms The integral time determines how long the PID regu- lator takes to correct the error. The greater the error, the quicker the integrator frequency contribution will increase. The integral time is the time the integrator needs to achieve the same change as the proportional amplification. 20 - 500 ms Noise in the feedback signal is dampened by a first order lowpass filter to reduce the noise's impact on the regulation. This might be an advantage, e.g. if there is a great amount of noise on the signal. See drawing. 100 ms Quick regulation is obtained through a short integral time.
However, if this time is too short, it can make the process unstable. If the integral time is long, major de- viations from the required reference may occur, since the process regulator will take long to regulate if an error has occurred. 0.00 (OFF) - 200.00 ms 20.00 ms Function: The differentiator does not react to a constant error. It only makes a contribution when the error changes. The quicker the error changes, the stronger the gain from the differentiator will be. The contribution is pro- portional to the speed at which errors change. Quick control is obtained by a long differential time. However, if this time is too long, it can make the proc- ess unstable.
When the differential time is 0 ms, the D- function is not active. If a time constant (t) of 100 ms is programmed, the cut- off frequency for the lowpass filter will be 1/0.1 = 10 RAD/sec., corresponding to (10 / 2 x π ) = 1.6 Hz. The PID regulator will then only regulate a feedback signal that varies with a frequency of less than 1.6 Hz. If the feedback signal varies by a higher frequency than 1.6 Hz, it will be dampened by the lowpass filter. 5.0 - 50.0 It is possible to set a limit for the gain provided by the differentiator. Since the D-gain increases at higher fre- quencies, limiting the gain may be useful.
This enables obtaining a pure D-gain at low frequencies and a con- stant D-gain at higher frequencies. 5.0 0.0 - 999.0 V Parameters 423-428 are used when in parameter 101 Torque characteristic a selection has been made of par. 103 = factory setting, () = display text, [] = value for use in communication via serial communication port 48 MG.29.A3.02 - VLT ® is a registered Danfoss trademark 418 Speed PID integral time (SPEED int. time) Value: Description of choice: 421 Spe ed PID lowpass filter time (spe ed filt. time) Value: Function: Function: Description of choice: 419 Speed PID differential time (SPEED diff. time) Value: Description of choice: Description of choice:
420 Speed PID D- gain limit (SPEED D-GAIN LIM) Value: 423 U1 v oltage (U1 voltage) Value: Function: Function: