Sensor status blinking red - not covered in manual

I just received my JS220 Rev B two days ago: manufactured 26 July 2023, serial 001841. Everything worked fine for two days, but now the sensor status is blinking red and the device will not accept any current. It does read voltages. There is no mention of the sensor status light in the manual. The rear panel light is a steady green.
Mousing over the fuse icons gives a message about a fuse being enabled and active, but does not explain which color means enabled: green, or gray? I can turn fuses 1 and 2 from gray to green by clicking on the icon that perhaps represents pulling a fuse, but this seems to make no difference. A careful microscopic examination of the board doesn’t reveal any obviously blown elements.


Hi @hthalljr and welcome to the Joulescope forum! Sorry to hear your Joulescope is not behaving as expected.

A slow red blink indicates that you have disconnected power. Is the power indicator blinking in the UI sidebar blinking?

A fast red blink indicates that the fuse has enabled. Is the fuse indicator in the UI sidebar blinking?

I am away from a computer now, but I will be back in about an hour. If you post more about what you see in the UI, I will take a look and respond then.

Here is the how the UI should look when functioning properly:

You can reset to defaults if you want. Select FileClear config and exit. You can then unplug and replug your Joulescope, although that should not be necessary. Then restart the UI.

Do you still see a flashing red Sensor Status LED?

Thank you for your prompt and informative reply. The light was flashing about once a second. I had made a newbie mistake and failed to note the change in status of the “lightning icon.” Everything is working well again.

I’m a bit confused about the “fuse” terminology. To me a fuse is a piece of metal that permanently melts (fuses) to open a circuit and must be physically replaced, and that was what I was looking for at first when I examined the circuit board.
Do I understand correctly that the Joulescope “fuses” are actually circuit breakers, which automatically reset themselves some time after “tripping?”

Thanks again for your help.

Tracy Hall Jr.

Hi @hthalljr and great to hear that you are back up and running!

Your Joulescope emulates a traditional melty metal fuse. Actually, it implements four different fuses simultaneously, and if any engage (trip), your Joulescope disconnects Current + from Current -.
Once the fuse engages, it stays engaged until you reset it. Those buttons in the UI allow you to reset the fuse allowing current to flow again.

As you already found out, your Joulescope can disconnect Current + and Current - under software & hardware control. It also has the ability to very accurately measure current with high bandwidth. The JS220 implements the fuses by running an algorithm on the captured current samples. If too much current flows through the JS220, the fuse will engage and stop current from flowing.

You Joulescope uses two of the four fuse channels to protect itself. The other two are optional, user configurable fuses that you can set for lower thresholds to protect your connected equipment.

You can read more about the details in the Joulescope JS220 User’s Guide in the Fuse section, currently section 12 on page 31.

Does this make sense and answer your question?

Yes, thanks. You’ve been very helpful.

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