First, your Joulescopes are already calibrated. While we do provide a validation procedure in the Joulescope User’s Guide Section 16.1, I doubt that is the issue. Just for reference, here is your previous post on current ranges. However, let’s start there.
Let’s confirm that your Joulescopes measure the same static current. I am going to assume that you have a power supply (PS), Joulescope A (A), Joulescope B (B), and a 1 MΩ resistor. If you don’t have a 1 MΩ resistor, you can often use a multimeter or oscilloscope input, which typically have a 1 MΩ to 10 MΩ input impedance. Connect the following:
- PS.+ to A.IN+
- A.OUT+ to B.IN+
- B.OUT+ to 1 MΩ.+
- 1 MΩ.- to PS.-
Now, power on your supply to +1V and start two Joulescope UI instances. Using the Device menu, select A in one and B in the other. Select Current Range to auto for both. What is the difference between the measurements?
Now, set both Joulescopes to the 18 mA range, but don’t change anything else. What is the difference between the measurements?
Now, use this same setup, except replace the 1 MΩ resistor with your target device. Set both Joulescopes to Current Range auto. What is the difference between the measurements?
With the dynamic data, you have to be very careful to get the same activity, otherwise your measurements will naturally differ because you measure different things. It looks like your data has some pattern that repeats every 5 seconds. When comparing data, add dual markers to measure over an exact number of these patterns. Does that change the result?
If not, I think that we need to look into the accuracy you should expect for your specific measurement. I am happy to take a more detailed look at your specific data. Could you share two JLS captures, one with Current Range set to auto and one with Current Range set to 18 mA? You can post using your favorite file-sharing method. If you would prefer to not share publically, you can email support at joulescope.com with the links to the files and this post.