I want to use a member of the INA210-INA214 family in one of my new projects.
i want to measure current with a shunt drops of 10mV full-scale (datasheet)
Lets take the 213, typical +/-5uV but the max. is +/-100uV
i want to measure high current AND LOW current with a range of 1000:1 (10 bit AD converter(1024)) meaning the LSB is 10uV (x GAIN)
now 10uV is above the typical 5uV but way below the max. 100uV, meaning a reading of 20 could mean 300uV (+100uV offset) or 100uV (-100uV offset), a huge error.
(always at least a 1% error full scale and much more with lower voltages +100%)
Am i doing something wrong?
Is the offset voltage constant on one IC initial and over time (constant temp), and if so is there an easy way to correct this?
BaWi,
In any application where you are measuring shunt voltage you will always have greater % errors at the lower input voltages because the offset of the INA21x will comprise a greater portion of the gained up output signal. You have to determine the minimum voltage that you need to measure and then determine the worst case error that you can live with, after which you can determine the size of your shunt resistor and then which shunt INA gain will work best for your application. If you are not converting current to voltage and are trying to measure voltage from the output of a sensor (as an example), you should consider using an INA such as the INA333 to do this.
If you would like to calibrate the offset and the gain error of your INA21x device, you will need a DMM with good resolution and use the following procedure:
(1) Input VinMin, measure VinMin, measure VoutMin
(2) Input VinMax, measure VinMax, measure VoutMax
(3) Calculate actual gain =
Gain_Actual = (VoutMax - VoutMin)/(VinMax - VinMin)
(4) Short the inputs to your nominal common mode voltage (i.e. 5V or 12V) and measure Vout
(5) Divide Vout by Gain_Actual to derive VOS.
*You can use Gain_Actual and VOS in all of your future readings so that the errors that they contribute can be removed from the readings
This way of correcting the offset was known by me and is usable but i was hoping for an even easier way.
Question about: Is the offset voltage constant on one IC initial and over TIME (constant temp), I assume it is constant as i can use the calculatied VOS for future readings and the datasheets mentions nothing about time.