When it comes to instruments for current measurements, you should always be able to find information about how accurate the measurements will be. You will find this in the terms of ±(gain error + offset error), ±(X% + Y), which means that your measurement value can be offset by an error of Y and have a percentual error X.
The accuracy for the main channel for low currents of Otii Arc is ±(0.1% +50nA). So, what does that mean when it comes to the real measurements? How does this affect the measurement accuracy? Let us compare the Otii Arc accuracy with another measurement instrument with a quite common accuracy of ±(1% +1uA).
Let say you want to measure a sleep current of 1uA.
When measuring with Otii Arc you can get the following result 1uA± 51nA (0.1% of 1uA is 1nA and then add 50nA = 51nA). If you use the other measurement instrument then the measurement can show 1uA ± 1uA (1% of 1uA is 10nA and then add 1uA = 1010nA). If you want an accurate measurement of the sleep current of 1uA and you measure between 0uA to 2uA it is obvious that this is not very useful.
To highlight this here is a table showing the absolute error (uA) together with the percentage error for different current measurements:
The accuracy for any instrument is usually specified for specific ranges of measurements. This means that you could get great accuracy for a small range of currents measured but also very inaccurate measurements for other ranges. Here is an example of the measurement errors across a wider range of current measurements, for a number of instruments on the market (the data is taken from the available datasheets):
So, you need to know your short and long-term needs when it comes to the accuracy in measurements. Consider all the ranges in the datasheet to understand how precise an instrument is. In some cases, you will need a precision instrument and will have to pay a lot for that one great feature. This is usually what traditional lab instruments offer. In other cases, reasonable accuracy works and you can go for instrument that offers great accuracy for a wide measurement range as well as more diverse features that can also help you in other aspects of energy optimization.
Having this in mind will help you pick the right tool for your development project and avoid yet another pitfall in getting that low current consumption of your device.
Products used in this article:
Power Analyzer, Log Sync & Power Supply in one Product. Otii Arc comes with the featured-packed standard Otii software (perpetual license).