VLT ® 2900 Series Load and Motor Constant torque (Constant torque) [1] Speed control, open loop (SPEED OPEN LOOP) [0] Variable torque low (torque: low) [2] Speed control, closed loop (SPEED CLOSED LOOP) [1] Variable torque medium (torque: med) [3] Process control, closed loop (PROCESS CLOSED LOOP) [3] Variable torque high (torque: high) [4] This parameter is used to select the configuration to which the frequency converter is to be adapted. This makes adaptation to a given application simple, since the parameters not used in a given configuration are hidden (not active).
Variable torque low with CT start (VT LOW CT START) [5] Variable torque medium with CT start (VT MED CT START) [6] Variable torque high with CT start (VT HIGH CT START) [7] Special motor mode (Special motor mode) [8] If Speed control, open loop [0] is selected, normal speed control is obtained (without feedback signal) with automatic load and slip compensation to ensure a constant speed at varying loads. Compensations are active, but may be disabled in parameter 134 Load compensation and parameter 136 Slip compensation as required.
CT = Constant torque This parameter enables a choice of principle for adap- tation of the U/f ratio of the frequency converter to the torque characteristic of the load. See par. 135 U/f ratio. Programming If Speed control, closed loop [1] is selected, better speed accuracy is obtained. A feedback signal must be added, and the PID regulator must be set in pa- rameter group 400 Special functions . If Constant torque [1] is selected, a load-dependent U/ f characteristic is obtained, in which output voltage and output frequency are increased at increasing loads in order to maintain constant magnetization of the motor.
If Process control, closed loop [3] is selected, the in- ternal process regulator is activated to enable precise control of a process in relation to a given process sig- nal. The process signal can be set to the relevant process unit or as a percentage. A feedback signal must be added from the process and the process reg- ulator must be set in parameter group 400 Special functions . Process closed loop is not active if a Devi- ceNet card is mounted and Instance 20/70 or 21/71 is chosen in parameter 904 Instance types . Select Variable torque low [2], Variable torque medium [3] or Variable torque high [4], if the load is square (centrifugal pumps, fans).
Variable torque - low with CT start [5], - medium with CT start [6] or high with CT start [7], are selected if you need a greater breakaway torque than can be ach- ieved with the three first characteristics. NB! Load and slip compensation are not active if variable torque or special motor mode have been selected. = factory setting, () = display text, [] = value for use in communication via serial communication port MG.29.A3.02 - VLT ® is a registered Danfoss trademark 19 101 Torque characteristic (TORQUE CHARACT) Value: 100 Configuration (Configuration) Value: Function: Description of choice: Function: Description of choice: