uCurrent Meter Question

[Cigarsnob]

Bought a couple of uCurrent the other week and they recently arrived.

I'm working on a device that is low power (microcurrent in the standby state) until you tell it to turn on and generate a waveform pattern. The device has a current output port, 0-3mA, through some restive load. At some frequency let's say 1kHz and up to 10kHz. This is my DUT.

The image below is my two attempts to measure the current of this DUT. The output of the uCurrent is connected to the scope. I expect the waveform from the uCurrent to match that of the DUT's output waveform along with all rest of the board's current draw. But I don't.

https://imgur.com/a/GaHARh4

I gotta be doing something wrong here. What am I not understanding here or messing up?

Thanks!

[sokoloff]

Other than "didn't work", could you be more specific? Give us a screenshot of the scope (if digital) or at least a trace of the expected and observed waveforms.

[JohnnyMalaria]

Based on my experience with the uCurrent, both the input and output -ve terminals are connected to ground (referenced to the power supply). I didn't realize this and couldn't understand why what was a perfectly functioning system without the uCurrent turned into a system that shorted the voltage I was supplying to my DUT. In my situation, I used an external supply rather than the battery. So, I'd expect Method 1 to fail. I don't know about Method since you have the uCurrent on the low side of the DUT. However, you shouldn't assume that the voltage waveform and current waveforms would be the same anyway. You may have capacitive/inductive effects going on with your DUT that would certainly affect the appearance of the waveforms. Without seeing example 'scope traces, it's impossible to say. Another point - are you actually measuring your DUT output voltage or are you assuming what it should be?

(My memory is a bit sketchy on this since I managed to overcome the problem and move on with my project The uCurrent is a great device)

[Cigarsnob]

Below is a scope pic of the output across a 1kohm load.

https://imgur.com/a/oF9cxAz

I expected my ucurrent to somewhat show a familiar trace to this. Not a complete copy, but something. Instead I just saw what appeared to be noise. I unfortunately didn't get a picture of the uCurrent output on the scope.

I'll try again though and maybe use a power supply this time.

[sokoloff]

One other tip, your scope can probably save screenshots directly to a USB drive. Knowing that is less for our benefit, but I find it handy to get in the habit of screen capping key things during projects and if I can do that from the scope, I find I'm more likely to do it than to pick up my phone and take a snap.

Not sure your model, but here's the instructions from another B&K scope:

To save waveform images to USB flash drive, follow the steps
below:
1. Select the screen image that you want.
2. Press the “SAVE/RECALL” button to enter
“SAVE/RECALL” menu.
3. Press the “Type” option button to select “Picture”.
4. Insert a USB flash drive to the USB host port of the
oscilloscope and wait until the oscilloscope has initialized
the USB flash drive (about five seconds).
5. Press the “Print Key” option button to save the
screenshot image to the USB flash drive

[JohnnyMalaria]

Have you tried averaging the signals with your 'scope?

For my application, direct viewing of the uCurrent output was quite noisy. Because I capture the voltage and current signals into a computer, I can apply a digital filter and get nice current traces. One limitation of the uCurrent I ran up against was the fact that the three ranges are factors of a thousand apart. So, you might have a load that is just beyond the full range of one setting and so you have to go to the next. As a result, you may only be one percent or so into the full range of that setting. Hence, you'd probably see weak, noisy output. My solution to this was to add more shunt resistors in parallel and use a mechanical DIP switch to select the desired shunt.

www.eevblog.com/forum/beginners/how-to-use-the-ucurrent-gold-with-a-voltage-divider/msg1430921/#msg1430921

[JohnnyMalaria]

Something else I remember regarding external power supply. I ended up using a 9V battery and a buck down converter. It gives long battery life and is easier to change because of how my device is buried away. I original tried a 19V source from a laptop supply + converter which powers everything else I need including a couple of RF power amps. Hence, I used a battery. I'm sure I could have just used another adapter + down converter but this was easier. It seems you have to keep the power to the uCurrent isolated from the rest of your system. You can operate the uCurrent  up to 5.5V (which is why I chose to use a different source) which gives you a wider full range. I use 5V just to be safe.

[Cigarsnob]

to Sokoloff...Yeah I know. I just didn't have a thumb drive with me.

[rmeldo]

Hi,

I am new to this forum. I hope it is ok to ask a question mildly related to the discussion.

I am trying to buy a ucurrent gold but everywhere I look I find that it is either discontinued or out of stock.

Does anyone know whether this is temporary or it out of production for good?

Any suggestion on where I can find one
Thanjs