Choosing Oscilloscope for Measuring Current

[Madhav Aggarwal]

Hello,

We are developing a wearable device with NRF52 as a Beacon with CR2032 coin cell battery. We need to measure current profile for the beacon and calculate corresponding battery life. For this we also referred to  Measuring current chapter in the nRF52 DK documentation. Now, in order to measure current profile as described in documentation, we are looking forward to purchase a digital oscilloscope with following configuration:

Hantek 6022BE: Bandwidth: 20MHz; Sample Rate: 48MSa/s; Vertical Resolution: 8bit

Can you please confirm whether it would serve our purpose as we are tight on budget to purchase expensive one. Or, maybe you can suggest some cheap alternative to it.

Thank you,

Madhav

[Madhav Aggarwal]

Hey,

Thank you for your prompt reply. I read the reviews on its HW and SW and they seem to be pretty good. Further below are its parameters: (kindly let me know whether to go for it or not as I am purchasing DSO for the first time)

Oscilloscope Features
Bandwidth	20MHz
Channel	2(Digital)+16(Logic)
Sample Rate	48MSa/s
Memory Depth	1M
Rise Time	17.5ns
Time Base Precision	±50ppm
Time Base Range	4ns/div-1h/div (Step by1-2-4)
Input Impendence	1MΩ 25pF
Input Sensitivity	20mV/div～5V/div
Vertical Resolution	8Bit
Vertical Position Range	20mV ~ 5V/div @ x1 probe; 200mV ~ 50V/div @ x10 probe; 2V ~ 500V/div @ x100 probe; 20V ~ 5KV/div @ x1000 probe
DC Accuracy	±3%
Bandwidth Limited	20MHz
Trigger Type	Edge, Alternative
Trigger Source	CH1, CH2

Thanks,

Madhav

[AmbystomaLabs]

Unless you happen to be really pressed for bench space or just require a portable solution, I would always choose a device with a built in monitor.  They boot fast and are always ready to go whether or not you happen to be looking up something on the web.

Plus the 48MSa/S rate of yours is pretty slow.  My scope is 1GSa/S and I consider it just sufficient.

My current scope is an old Agilent 2 channel.  But, if I were looking at scopes I would definitely get a 4 channel. Virtually all modern test equipment has ethernet and usb ports so you can easily capture screens and data on a PC.

Though I don't own a Rigol, I have seen them at the ESC conferences and it seems like a nice and very inexpensive machine with very good reviews.  If I were in the market for an inexpensive 4 channel it would be my top choice.  Only $349 at amazon.

www.amazon.com/.../B012938E76

[awneil]

I do own a Rigol and can thoroughly recommend it for this kind of work.

But have you looked at the Nordic Power Profiler Kit?

https://www.nordicsemi.com/eng/Products/Power-Profiler-Kit

[Madhav Aggarwal]

Yes, I have checked Nordic Power Profiler Kit, and it looks quite promising, but I am specifically looking for an inexpensive oscilloscope. I am in a fix now whether to go for 48MSa/s scope which is only $84 on Amazon and portable too, or shell out more money to get Rigol.

It would be great if you can please clarify me on trade off between the two. 

[AmbystomaLabs]

If your absolute limit on price is under $100 you should thumb around on Ebay first.  There are often a lot of reasonable quality devices like the Hantek that may have better specs.

I tend to think of all my tools as investments. Either I am saving time, money, fostering my career or all of the above.  I assume you will want to do more with this scope than measure BLE power consumption.

The problem you will run into with a 48MSa/sec scope is that even things at Pclk speeds (16MHz) will show up as a sine wave on it simply because the nyquist frequency is only 24MHz. Trying to get a scope to lock onto a sine wave is fraught with difficulty unless the amplitude is really steady.

However, on a reasonably fast scope such as the Rigol, a 16MHz signal shows up as a nice square wave since its nyquist region comfortably holds 31 harmonics of the signal.  Suddenly measuring the phase difference between two 16MHz signals is easy.  And frankly 16MHz clocks are pretty slow these days.  Likely you will soon want to work with faster signals and processors.

[haakonsh]

I agree with AmbystomaLabs. If you're short on resources you should invest in a more general tool. I cannot recommend the PPK to an engineer in your position, and you'll need an oscilloscope in the future anyways. 

The PPK is great for ease of use, but it is not as good of an investment as an oscilloscope.