I have some experience with digital circuits and microcontroller programming but no prior experience with or knowledge of industrial equipment like motors/pumps. All in all, a newbie.
To continuously monitor the current drawn by a water pump connected to a 3-phase AC induction motor and if the current drops below a certain threshold, trip the motor. Need to figure out a simple, elegant and cost-effective way to accomplish this task.
My research results:
I found two ways to implement AC current sensing:
1) Current transformer
2) Hall-effect sensors
Both provide DC voltage proportional to the sensed AC current which can be measured in a digital circuit. I have decided to go with hall sensors for reasons of size and accuracy.
To connect the three phase wires to hall sensors. The sensors will produce voltages proportional to the sensed currents. These voltages will be fed to a microcontroller via ADC and the controller will operate relays based on the voltage reading i.e. it will trip the motor if sensed current is below a pre-defined value for the motor.
I understand that I could do away with the controller and get my work done with comparators that drive those relays, but I want to keep the "threshold" configurable, so going with a controller instead. And also there is the scalability factor.
- Is the choice of hall sensors over current transformers justified, given my requirements?
- Does the decided approach pack promise?
- Is there a better, more generally accepted way of doing this that i am oblivious to?
- Can the duo of input hall sensors and line tripping relays be replaced with a single such device which can not only measure the current but also break the circuit?