Low Side Current Measurement

Alexandre Imbeault said:

Hello, I want to use a current shunt monitor (INA214) with a shunt resistor of 0.000167 ohms with a current passing through of -300A to 300A this correspond to a voltage drop of 50mV. Is it possible to use the current monitor on low side and read a bi-directionnal voltage from -50mV to 50mV?

Thank you

Hello Alexandre,

I'm not sure whether 0.0000167 ohm shunt is available.. seems to be a non standard value. Correct me if I'm wrong.

Why don't you consider Hall effect current sensors for your application ?

Regards,

JayantD.

Thank you for your answer Jayant,

If you look at Murata shunt resistor 3020-01102-0 you will see that it's a 0.000167 ohms resistor rated for 300A/50mV. It seems logical because 0.000167*300 = 50mV.

I have already consider Hall Effect and according to my research, I can't have the accuracy I need with these current sensor. For several days I looked for the best solution for my problem and I think shunt current sensor would be the best. Correct me if I'm wrong because I begin in the field of electric vehicule.

I need a precision around 100mA to evaluate correctly the State Of Charge of my batteries. And I don't need to be isolated that's why I though of shunt current sensor.

Could you help me out with this problem?

Since the shunt resistor is in the low side (ground-referenced) why not simply use a good instrumentation amplifier? It will give outstanding accuracy with a 50mV input and its gain is easy to set accurately.

Make sure that the shunt resistor is a Kelvin-sensing (4-wire) type!

Thank you for your answer Neil,

Do you have a good instrumentation amplifier tu suggest to me for my application? And will I be able to measure bi-directionnal current?

I'm not sure to understand how to proceed, could you please give me more information about this method?

Alexandre;

I've attached a chapter of my Instrumentation Amplifier Handbook for you; check section 7.2. Bear in mind that this is a draft copy-- it never was published although it can be found all over the internet, sometimes as an earlier enedited version.

If you use an instrumentation amplifier with bipolar power supplies, the output can swing + and - for bi-directional current measurement.

Neil, Thank you for your handbook, It is really useful for better understanding.

The problem is that I'm in an automotive case, so I only have single power supplies and I don't want to create a bipolar power supply only for this application. I would appreciate to find an instrumentation amplifier with a +5V single power supply.

Thank you for your answer Pete, sorry if it takes me a while to reply but I'm not sure to understand everything you said. According to what you told me, I won't be able to have a precision of +/-100mA on current measurement with the INA214. So, do you have any idea of how should I proceed? Should I use a instrumentation amplifier like Neil Albaugh suggest?

Best regards,   Alexandre

Thanks, Alexandre.

The IA shown in the Handbook is still a good one-- its common mode input voltage will go to zero and with a load of 20k the output will swing up to 50mV below the supply rail and down to within 100mV of ground.

There are more modern 5V CMOS instrumentation and difference amplifiers that can do better than this but the TI instrumentation amplifier parametric selection guide is such a mess that I gave up trying to find a good one. Maybe a TI employee can either fix the thing or struggle through it to make a recommendation.