I have negative voltage rail of -2v. will js110 will measure the power for -2v?

Technical Discussion
1

I have negative voltage rail of -2v input . will js110 will measure the power for -2v?

2

i have connected external power supply of -2v to IN of JS110 and OUT of JS110 is connected to DUT. while in GUI oscilloscope measurement I see -1.5V instead of -2v. I measured the voltage at joulscope IN/OUT terminals its exact -2v, but why its showing -1.5v in GUI?

3

Hi @pushpa and welcome to the Joulescope forum. The first-generation Joulescope JS110 has always been a (mostly) 1-quadrant instrument measuring +current and +voltage. Here are the specs from the Joulescope JS110 User’s Guide:

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image1111×395 73.1 KB

While the measurement range does extend slightly negative, it is definitely not symmetric. Also, the JS110 only contains fast autoranging in the +current direction. While negative saturation varies slightly from instrument to instrument, -1.5 V is pretty typical.

The second-generation Joulescope JS220 is a full symmetric, 4-quadrant instrument with fast autoranging for both +current and -current. From the Joulescope JS220 User’s Guide:

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If you need fully symmetric measurements, please consider upgrading to the JS220!

4

Hi,

Thank you for your response. Can you also please clarify below.

  1. So can I also give -4V as input using js220?
  2. will same GUI work for js220 as well?
  3. Can you give connection diagram to drive input to joulscope from external supply(vary the voltage) and connecting its output to DUT. I want to measure voltage,current and power all 3.
  4. Can you also confirm if JS220 v+v- and I+I- is same as JS110 in+in- and out+out- ?

Regards,

Pushpa

5

Hi @pushpa

Yes. Anything from -14.5 V to + 14.5 V.

Yes, the Joulescope UI and Joulescope Python packages support all Joulescopes (JS110 and JS220 as of 2025-09)

From the Joulescope JS220 User’s Guide, currently revision 1.10 on page 22:

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The JS110 shorts together V+ and I+ on the instrument:

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The JS220 allows you to wire voltage and current separately, which means you can make 4-wire Kelvin connections. Look at the start of section 9 on page 18 for more details.

6

Hi,

I have to connect JS220 in between header pin 1 and pin 2. Can you please draw connections to JS220 please. I made a connection but power i am reading in nW. so wanted to confirm my connections.

pin 1 and pin 2 of jumper i shorted and connected to = V+ of joulscope

ground pin of jumper i connected to = V- and I+.

Note: its -3.5V rail

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image868×381 8.33 KB

Regards,

Pushpa

7

Hi @pushpa - Are pins 1 & 3 the same and 2 & 4 the same? I am guessing you duplicate them to achieve some current rating specification. In normal operation, I am guessing you short 1 & 2 and 3 & 4 using a jumper.

Your JS220 measures the current flowing from I+ to I-, and the voltage across V+ and V-.

I am going to call your jumper J1 and the Joulescope JS220 JS220.

First, remove the jumpers you normally install

  1. J1.1, J1.2
  2. J1.3, J1.4

Here are the connections:

  1. J1.1, J1.3, J220.I+, JS220.V+
  2. J1.2, J1.4, JS220.I-
  3. J1.GND, JS220.V-

You want to wire together (short) all endpoints indicated in each line.

This measures the current flowing from J1.1 & J1.3 through the Joulescope and back into J1.2 & J1.4. It then measures the voltage from J1.1 to J1.GND.

Does this make sense and measure what you care about?