Hopefully some seasoned electrical engineers will have some insight here. I am making a current sensor on a motor controller. This sensor will be made using shunt resistors in parallel (kelvin sensing will be used). I need to measure 0-70amps with at least 1% accuracy/precision and 10ma resolution.
I am using 0.01mOhm resistors (3 in parallel), these are 5W resistors. (we will only be measuring a MAX of 60A continuously, and I have very nice heat sinks, yes the resistors are designed for kelvin sensing)
The issue is 10mA is represented as 33.333uA with such small resistors and such a large range of current.
I am damn sure that my design will read with this resolution(24bit adc) and accuracy/precision right now, EXCEPT my voltage reference needs to be more precise. I am using a 2.048Vref with 0.02% MAX initial tolerance. This leaves me with a whopping 409uV max uncertainty of initial offset error!!! I cannot find a more precise voltage reference than the one I am using.
Finally~ I am sure that if I can CALIBRATE the board at assembly, it will have the readings I am looking for. Does anyone know of methods for doing this to fix the offset which is constant? Rather than look for a better Vref I would rather find a good calibration process. This could eliminate other offset error and parasitic problems as well, and fix and long term drift in the future.
Thanks for taking you time to help!
I am using 0.01mOhm resistors (3 in parallel), these are 5W resistors. (we will only be measuring a MAX of 60A continuously, and I have very nice heat sinks, yes the resistors are designed for kelvin sensing)
The issue is 10mA is represented as 33.333uA with such small resistors and such a large range of current.
I am damn sure that my design will read with this resolution(24bit adc) and accuracy/precision right now, EXCEPT my voltage reference needs to be more precise. I am using a 2.048Vref with 0.02% MAX initial tolerance. This leaves me with a whopping 409uV max uncertainty of initial offset error!!! I cannot find a more precise voltage reference than the one I am using.
Finally~ I am sure that if I can CALIBRATE the board at assembly, it will have the readings I am looking for. Does anyone know of methods for doing this to fix the offset which is constant? Rather than look for a better Vref I would rather find a good calibration process. This could eliminate other offset error and parasitic problems as well, and fix and long term drift in the future.
Thanks for taking you time to help!