VLT ® 2000 Series I Load and motor (group 1..) (continued) Closed loop control - PI controller: If closed loop control is required, the transmitter, tacho-meter or encoder should supply one of the analogue standard signals (e.g. 0-10 V, 0-20 mA, 4- 20 mA ) or a pulse signal frequency of max. 100 Hz, 1 kHz or 10 kHz (programmable). The reference signal can either be fixed internally (di- gital reference) or be a standard analogue signal or pulse signal. The feedback value should be 50-80% of the reference signal. It is not possible to select the same type of signal (voltage, current, pulse) for both the reference and the feedback.
At start the ouptut frequency is determined by the reference and the feed forward factor (parameter 119) and the f MAX and f MIN settings of the frequency converter. When a feedback signal is registered, the PI controller then corrects the ouptut frequency by comparing with the reference/feedback signals. At stop the output (integrator) is set to 0 so that a restart follows the normal start situation. The control possibilities of the VLT Control with closed loop Section 1 Section 2 Section 3 MG.20.B6.02 – VLT is a registered Danfoss trademark 53