Rexroth Tightening System 300 Power Supply Modules and Servo Amplifiers The VM300 power supply module is used to supply power to all the cards in the card racks or in the system boxes. One VM300 is required per card rack or system box. The digital servo amplifier controls the EC motor. The control parameters are digitally transmitted from the SE to the LT. An important factor for emergency-off is the integrated motor contactor.