Hi Jan, and welcome to the forum! Thank you for considering a Joulescope for your application. I took a quick look at your website. Cool projects!
The Joulescope JS110 is mostly a 1 quadrant device, +current and +voltage, with some measurement range extending into the other three quadrants. The Joulescope JS110’s fast current autoranging only works in the +current direction. It will still autorange on -current, but not quite as fast. Based upon your high-voltage DC regulator work, I am going to assume that you want to measure 2 kV DC currents.
The JS110 should work just fine measuring currents up to 3A sustained. If you want to measure voltage so that you can also measure power and energy, you can select a suitable high-voltage divider circuit. Check out this post for details. If you only want to measure current, connect IN- to IN+ and leave OUT- open.
That Intona USB isolator looks good, and 500 mA is enough to power the Joulescope JS110. The Joulescope JS110 sensor-side is also electrically isolated. For details, see page 27 of the Joulescope JS110 User’s Guide. However, our standoff voltage is further limited by the aluminum case and spacing between the USB chassis ground card rails and the sensor electronics. The JS110 also does not have any safety certification for higher voltages and is only rated for low-voltage ±48V DC. For your work, I definitely recommend a second isolator like you have selected.
Consideration 1
With two isolators, the working voltage will split somehow across them. You likely want to deliberately force Joulescope’s host-side ground to be close to the sensor-side. The JS110 components are not rated for this stand-off voltage, so you really want the majority of the working voltage drop across the Intona isolator. You could add a very high-value, high-voltage rating resistor across the JS110’s isolated plane split. I would guess that the best place would be near the transformer away from the sensitive analog components. Assuming the resistor is not too thick, you could bridge the isolated gap on the backside by scraping away some solder mask and soldering the resistor there. If you order from the Joulescope store and make a note “Send dead bare-board” on your order, I will include a dead bare-board with your order so you can practice. You can also order from our distributors, but I don’t have a way to include a bare-board.
Consideration 2
High dV/dt is also a concern. All isolators allow some coupling, especially for fast transients. We have had reports of JS110’s resetting on ESD events, even on the sensor side, likely due to coupling to the host side. I have not done enough testing to know whether this is through ESD directly leaping to the USB chassis ground or through the isolation components. While USB is a somewhat differential bus, the common-mode voltage range is very small, only 0.8V to 2.5V. While it’s very hard to know definitively, we believe that many of these reset events are caused by coupling that causes ground bounce which violates this constraint causing USB errors and eventually a host-initiated reset. With a higher input voltage range on the sensor side, your setup has the possibility to have higher dV/dt events that may cause this issue. However, if your voltage ramps at reasonable rates and is mostly stable, this should not be an issue.
Consideration 3
Joulescopes use MOSFETs to selected the shunt resistors and disconnect IN+ from OUT+ when the JS110 powers off or you set Current Range to off. If this ever happens in your system, then the JS110 will see your full voltage drop across IN+ and OUT+ which will definitely fry the 10A & 2A selection range MOSFET. I recommend that you add two diodes, one in each direction, across IN+ and OUT+. While these diodes may cause a little bit of unmeasured leakage current, they will help prevent you from blowing up your Joulescope. You want to select diodes that handle your current with minimal leakage at up to 25 mV forward or reverse bias.
Safety First!
Joulescope’s aluminum enclosure, screws, end panels, and exposed USB chassis ground will all be at or near your operating voltage. Good engineering practice is to limit the chance of accidental contact. You may want to wrap the enclosure or 3D print guards.
The proposed setup has the possibility to inadvertently operate the Joulescope JS110 beyond its rated limits. Please be sure to follow all safety practices including having a quick emergency shutdown and fire extinguisher, just in case.
Does this answer your questions?
What do you think?