Thread Starter

Danielle Singh

I wish to control a servomotor using a 4-20mA output from a PLC. does anyone have a circuit that can control the motor using the 4-20mA signal. the servo motor has 5 pins : 2 motor power (+ ,-) and the other 3 are connected to a feedback potentiometer

Shantanu Apte

1) You should have a PLC with analog input and analog output CARD . Also should have High Speed Counter Module to process feedback form Encoder. 2)Because of the sturdiness of Resolver , most of the popular servo motors come with integrated resolver . 3) Connect the PLC's analogue out (configured as +/- 10 V or 4 - 20 mA) and connect it as COMMAND to Servo Drive . 4) Connect Resolver signal from Motor end to the Srvo Drive . Most of the servo drives have built in circuitary to convert that signal in Digital compatible form . This signal to be fed at the high speed counter module of the PLC.Thus your PLC will see as if Encoder is connected. 5) Now , you have completed this feedback loop. Take care of HOME,End Limit and other inputs and build ligic. Make U V W connection from Servo Drive To Servo Motor . 6) Most of the Drives come with tunning parameters software, try to put all relevent information and try playing with P I D gains . REMEMBER TO RUN THE MOTOR WITHOUT LOAD ! once satisfied start putting load . Refer to manufacturers data sheets and work carefully. 7) In above mentioned steps 1-5 , you have closed : Current Loop : Drive Velocity Loop : Drive Position Loop : PLC 8) If position accuracy is atmost important then PLC may not be RIGHT choice . Try for some good programmable multiaxes controllers like Delta Tau make PMAC . I have used it and is great ! In case of any doubt . Get back to me . Shantanu