My background:
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.
My requirements:
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.
Decided approach:
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.
My questions:
- 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?