The Schneider Electric VW3A3E408 is a resolver encoder interface module for the Altivar drive range. It accepts resolver feedback and converts it to a digital speed signal the drive can close the loop on — critical for position-regulated axes or low-speed torque control where an incremental encoder would drift. The module supports selectable transformation ratios of 4:1, 3:1, 2:1, and 1:1, so it matches resolvers with different primary-to-secondary turns ratios without an external scaling transformer.
Excitation and feedback parameters
Excitation voltage is adjustable between 1.25 and 5.6 Vrms, with a maximum excitation current of 50 mA — enough to drive most standard resolvers up to 200 m of cable. The excitation frequency is field-selectable at 4, 8, or 12 kHz; the 4 kHz setting suits longer cable runs where capacitive losses would otherwise attenuate the carrier, while 12 kHz gives a faster update for high-speed spindle applications. Secondary voltage is fixed at 1 Vrms, which is the resolver's output at the rated transformation ratio.
Speed resolution and pole matching
Speed feedback resolution is 12 bits (±1 bit), giving 4096 counts per revolution at the maximum pulse count. The module supports motor pole counts of 2, 4, 6, or 8, and automatically pairs the encoder pole count (2, 4, 6, or 8) with the motor poles to keep the electrical angle aligned. Maximum shaft speed depends on the pole combination: 7500 rpm with 2 motor poles and 4096 pulses per revolution, down to 1875 rpm with 8 motor poles and 512 pulses per revolution. This pole-matching logic is what lets the drive compute rotor position without an external cam or hall sensor.
Connection and wiring
Electrical connection is via screw terminals accepting 0.2 mm² to 1 mm² (AWG 24 to AWG 17). The maximum cable distance between the module and the resolver is 200 m, provided the cable capacitance and the excitation frequency are within the drive's guidelines. For a 12 kHz carrier, keep the cable under 100 m to avoid signal degradation; 4 kHz allows the full 200 m.