Joulescope : autoranging and dynamic range

Technical Discussion
1

Hello,

I’ve recently discovered the joulescope, and I am trying to understand if it offers the performances I need for some measurement.

Basically, I want to measure a current profile similar to the one below

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  1. The device in in Idle for several ms, current consumption is about 15mA.
  2. There is a 200us peak, with a max current value around 100mA (Could go as high as 140mA)
  3. Following the blink, device goes to sleep and current consumption is down to less than 10uA.

Does a jouloscope has sufficient dynamic range and resolution to perform such measurement ? I’m particularly interested in the Peak to sleep phase that is very quick, and I wonder if the measurement will be fast enough to display the peak.

I suspect the device may not be able to measure the 200us peak with spike at 100+mA with a sufficient resolution. Is the 250KHz bandwidth sufficient for such measurement ?

Also, the current goes from 100+mA to <10mA within one ms. Does the joule scope has sufficient resolution to provide such current profile ?

The first table page 11 of the user manual makes me think that the joulescope cannot measure both current around 100+mA, and current within 10uA accurately (as the resolution for the 180mA range is 15uA).

It sounds like there is an auto-ranging feature allowing the device to switch between different current measurement range. Will this auto-ranging be fast enough in my case knowing that the blink is only 200uS ?

Thank you very much for the help,
Kind regards
Yves

1 Like
2

Just for information, this is the table I am referring to:

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1 Like
3

Hi Yves (@YBdecawave)! Welcome to the Joulescope forum, and thank you for considering Joulescope for your application.

What sets Joulescope apart is its fast autoranging. Joulescope autoranges to higher current ranges in less than 1 µs (typical). However, it can take up to 5 µs after autoranging to measure the correct value. This introduces a brief time of measurement uncertainty that can affect the accuracy when measuring very short pulses. The specs are further down on that same page:

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The Joulescope software applies a filter on current range switching events, and you have full control over it. Here is what the filter settings look like:

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The 250 kHz bandwidth can observe a pulse of about 1/250kHz / 2 = 2 µs. Although application requirements vary, you normally want a ratio of about 5x to 10x from your measurement bandwidth down to your signal bandwidth.

In your application, is 200 µs the width of the ~50% level of the pulse (the time above the thicker white line)? If so, a Joulescope would be great for your application. Otherwise, would you let me know the approximate duration that the pulse is above the thicker white line in your plot?

If that pulse is very short, you do have another possibility of using two different configurations with Joulescope. To accurately see the pulse and iterate on that part of your measurement, put Joulescope in the fixed 180 mA range. As you noted, the offset accuracy will not be good enough in that fixed range for accurately measuring sleep current. Then, when you want to measure full current/energy consumption, reduce your signal bandwidth by adding capacitance to your target, and put the Joulescope into autoranging mode. This will allow Joulescope’s autoranging to work more accurately. Joulescope 180 mA range uses a 0.11 Ω shunt, so if you want to reduce the bandwidth to 50 kHz you would need:

f = 1 / (2 π R C)
C = 1 / (2 π 0.11 50000) = 29 µF

4

Hi mliberty,

Thanks for the quick answer.

The thick white line corresponds to the trigger at 30mA.

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The pulse lasts 266us above the trigger, as you can see with the markers on the graph above.

So according to you, the joulescope should suit my application well and measure such a blink accurately, as well as measuring the sleep current correctly ?

Also out of curiosity, how long is the delivery time for the joulescope at the moment (USA or Europe?)

Thank you very much,
Regards
Yves

5

Hi Yves,

Thanks for the additional information. Based up that plot, a Joulescope should be a great fit to measure the active current, that pulse, and the sleep current. You just need to leave the Joulescope in the default autoranging mode. It will also be much less expensive and easier to use than your existing equipment :wink:

If you place an order on the Joulescope store by 3 pm EST USA (UTC-5), your Joulescope will ship today. Orders ship from the US, and typically arrive in the EU within 2-3 business days if you select UPS worldwide express. If you need the business quote/PO/invoice, we can do that, too. DM me here or use the contact form.

Let me know if you have additional questions!

  • Matt
6

Hi Matt,

Thanks for the additional info.

My manager has ordered one (customer is Decawave), I let you know if we have any feedback !

Thanks again,
Yves

1 Like
7

Hi Yves (@YBdecawave),

Great! I see the order, and your Joulescope will ship today. I hope that it helps you build even better products, and I look forward to your feedback!

All the best,

  • Matt