Method and apparatus for monitoring motor current for an electric valve positioner

A method of controlling a field device in a control system including a controller and a threshold current level stored in a memory device, the method comprising:

• detecting an occurrence of an event trigger;
• sending, by the controller, a control signal to a motor to actuate the field device in response to detecting the occurrence of the event trigger;
• monitoring, by a current sensor, an electrical current provided to the motor;
• comparing, by a comparator, the monitored electrical current provided to the motor to the threshold current level;
• providing, by the comparator, a state signal to a gate coupled between the controller and the motor, wherein the state signal provided to the gate places the gate in a first state enabling the control signal sent by the controller to pass to the motor when the current sensed by the current sensor is less than the threshold current level, and wherein the state signal provided to the gate places the gate in a second state preventing the control signal sent by the controller to pass to the motor when the current sensed by the current sensor is equal to or greater than the threshold current level.

A control system for controlling a process, the control system comprising:

• a field device coupled to the process and arranged to control a process condition;
• a motor coupled to the field device and configured to move a portion of the field device;
• a controller including a processor and a memory, the processor being operatively coupled to the motor for controlling the motor to move the portion of the field device;
• a current sensor coupled to the motor and arranged to monitor electrical current drawn by the motor;
• and
• a control module coupled to the controller and capable of regulating passage of control signals transmitted to the motor for moving the portion of the field device, wherein the control module includes:
• a gate having a first state and a second state, the gate including a control input and a control output, wherein the control input of the gate is coupled to a control output of the controller, and
• a comparator coupled to the current sensor and the gate, the comparator including a threshold current level and being capable of providing a state signal to the gate in response to a comparison of the current sensed by the current senor and the threshold current level, wherein the state signal provided to the gate places the gate in the first state enabling a control signal sent by the controller to pass to the motor when the current sensed by the current sensor is less than the threshold current level, and wherein the state signal provided to the gate places the gate in the second state preventing the control signal sent by the controller to pass to the motor when the current sensed by the current sensor is equal to or greater than the threshold current level.