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Tightened up the Measured Current Value

A project log for Computer Control for an old Electronic Load Box

Adding utility to a piece of 1970's test equipment.

bharbourBharbour 01/06/2024 at 17:150 Comments

As mentioned in the details section, the measured current value did not track either the set current value or an externally measured current value very closely.

Data from the software that I wrote to capture externally measured current, and internally measured current at many different current control DAC settings was used to calculate better slope and offset values for the INA230 measured current values. The INA230 measures the voltage dropped across a sense resistor (5 milliOhms), and that value gets turned into a current value: measured_current = (Sense_Voltage * measured_i_slope) + measured_i_offset.

Before messing with the slope and offset values, I plotted the difference between the calculated current and the externally measured current at multiple values of current. The difference was a relatively straight line with a small vertical offset. This showed me that the error was linear enough to correct easily.

The default value for the slope was calculated from Ohms law. The errors were small enough to attribute to part tolerances. After a few iterations, the measured current value is within 10mA at 7.000 amps.

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