I have connected two of the Joulescope JS220 devices to a power supply, and so I’m receiving incorrect values from both devices. The devices sometimes shows significant noise. Could this be due to a firmware issue? Both devices have been used for an extended period without any problems until now.
Thank you in advance,
Stefan
Hi @kunf and welcome to the Joulescope forum! Sorry to hear that you are having issues with your Joulescope, and thank you for sending the pictures. It looks like you have V+ and V- connected, but you left I+ and I- open.
The JS220 intentionally omits the pull resistors, typically 10 MOhm, found in other test equipment. While this allows excellent leakage performance, it does mean that you need to keep V+ and V- within 15 V of I+. The easiest way to do this is short V+ to I+, like this:
See page 20 of the Joulescope JS220 Users Guide.
Does this fix the issue for you?
Hi @mliberty,
Yes it did, thanks a lot for your help. Here, we have a classic case of RFM (Read the fu*** manual) ;). I usually measure the voltage and the current, so I have never noticed this effect. Funnily, it can be observed in my case that the noise only occurs when the laptop is connected to the power supply (and the DUT is wired incorrectly). At first, I didn’t understand why the measurement suddenly became noisy, but I probably just plugged my laptop into the power supply. I only suggest adding a corresponding note on the front panel of the Joulescope because of how the labels for “Voltage” and “Current” are now; one could easily assume that the measuring instruments operate independently.
Hi @kunf - I think that it is pretty common that the Joulescope JS220 just works and people don’t have to think about this. This issue does not normally occur unless measuring voltage only.
We do have the ±15 V spec on the front panel. This actually means both ±15 V differential and ±15 V common mode from Current + (or -). We don’t have a lot of room for text on the front panel.
The quick start guide says "The voltage between any current and voltage sensor port must never exceed ±15V. It does not say that they have to be connected relative to Current +. We could add, “When measuring voltage only, connect Voltage + to Current +”. Would that help?
Hello @mliberty,
We discussed the issue within our research team, especially considering the students, as we provide the devices to them. The devices are very compact, intuitive to use, and still allow precise measurements, making them ideal for our students.
A note in the quick start guide would be beneficial. Is the quick start guide also available online as a PDF? I couldn’t find such a document. With the students in mind, it would be great if one could send them the quick start guide (of course, we expect the students to read the entire user guide before using the device, but you know how students are 
).
Additionally, an adjustment on the front panel might also be helpful, such as:
Such a note doesn’t need to be fully self-explanatory. Still, it provides a hint to study the manual or serves as a reminder to make the connection, especially since the new JS220 front panel design envisions independent measuring instruments for current and voltage, as also presented in the Theory of operation in the guide:
Hi @kunf - Great to hear the Joulescope JS220 is a great fit for your students! I just posted the JS220 Quick Start Guide.
Thank you for your feedback. In general, not accounting for the input stage leakage currents is undesirable as the apparent input voltage drifts. This was a concious design choice with the Joulescope JS110 and JS220 as it does give the lowest possible input leakage current. Most customers never even notice that it is an issue since they hook up their Joulescopes. However, if we could have zero voltage drift for zero cost and zero leakage current, we would do that
The JS220 design is done. While we may have one or two more lot builds, we are now focusing on designing the third generation products. Unfortunately, this also means that we will not be making any modifications to the JS220 front panel or quick start guide.
Have you considered printing small stickers to add to the front panel or the top of the instrument?
We are considering options to improve this for the next generation products, such as PhotoMOS / OptoMOS SSRs. We will certainly look to incorporate your feedback into the next generation products!
