Comparison between armature controlled and field controlled DC servo motor : Field controlled DC servomotor Armature controlled DC servomotor 1. Field is excited by control voltage Armature is excited by control voltage 2. Armature current kept constant Field current kept constant 3. Required low power amplifiers are simple to design Required high power amplifiers 4. Efficiency is poor Efficiency is better 5. It has large time constant It has small time constant 6. Cost is low Cost is high 7. It is open loop system It is close loop system Comparison between ar