Review of the Cleverscope Frequency Response Analyzer

[rbola35618]

The view is a video review of the Cleverscope Frequency Response Analyzer's capabilities. The Cleverscope is a lower cost alternative to more expensive FRAs. I show its capabilities and some of its limitation and how to work around them to get accurate measurements of the control loop response.

The Cleverscope's software has been improved and I show its improvement in the low frequency measurement and compare them against a far more expensive FRA.

[Mark_O]

The Cleverscope's software has been improved and I show its improvement in the low frequency measurement and compare them against a far more expensive FRA.

Thanks, Robert.  It looks like it's now tracking the Venable very closely, from 10 Hz to beyond 20 kHz.  Both in amplitude AND phase.  That's a pretty significant improvement.

I like the Cleverscopes, especially the power that having the analysis/display running on a PC provides.  However, it's the $1200-2200 price tag, coupled with the max 100 MSa/s limitations that keep me away.

OTOH, if you need something specialized, like the FRA capability that approximates a $30k instrument, then the price tag on the Cleverscopes is effectively quite low.  However, even there, I'd like to see better automation capability.  And it wouldn't surprise me if they got there.

[rbola35618]

Hi Mark,

I agree with your comments. In todays economy, you need to have enough justification to make a big purchase. In my case, I design power supplies and I have a home lab. My needs were that I wanted to take my prototypes home to test and needed a FRA to perform loop response. I couldn't check out the Ridley or the Venable from work and take them to my home. I therefore found the Cleverscope who's capabilities have been significantly improved. For those that do not have a FRA, you can do the Poor man's FRA as shown in the link below by using your function generator and a scope.



The Auto function does work. I will probably do a video showing how it works. Since I was using an injection transformer and has a 20dB attenuation and I think if slow it done. I think hooking directly with out the injection transformer the Auto function should work better; I will try to verify this.

Best regard
Robert

[mswhin63]

For a USB scope it specs are quite nice, maybe a bit limited in refresh rate but for the PC based scope not bad at all.

Still standalone scope are still a good preference and a lot of them now have USB connectivity, the faster waveform update and the ease of controlling the scope is much better than a PC based one.
After a difficult marriage that ended many year ago i lost all my test equipment and was locked out of getting anything till about a year ago. My first scope to get me by was a PC based scope and although control were good for a PC scope it still doesn't come close to the standalone unit which I have now at a fraction of the cost of the Cleverscope.

[Alextsu]

Hi, Robert,
What do you think about the capabilities of some virtual software instruments based on PC Sound Card  Measurement System, for instance, this one:
http://www.virtins.com/multi-instrument.shtml
Another one is ARTA STEPS software http://www.artalabs.hr/download.htm
How do you think, are they suitable for carrying out FRA measurement for SMPS?
Or the signal-to-noise ratio would be poor there?
The VIRTINS Multi-Instrument softare has a feature of Bode plot (Gain/Phase) measurement, but it is based on a white-noise (broadband source) excitation technique.
Regards,
Alexey

[rbola35618]

Hi Alexy,

I saw the multi-instrument software. It looks interesting. Someone would have to test it with power supply and see how well it works.

But keep in mind that the Cleverscope has an isolation function generator. This means that you do not need an injection transformer as other FRAs such as the Ridley and the Venable. In edition, the Cleverscope has a capability of varying the amplitude of the injection signal as it sweeps the frequency. Normally, you need about 3 Volts peak to peak from 1 to 1000 Hz, but then you have to lower the amplitude to about 100mV once you get to about 100KHz. The feature makes it possible to take very stable open loop plots without noise showing up in the plots. Overall, I am very happy with my Cleverscope. Bart has continued to update the software and has implemented an  LCR features as well. I hope this helps.

Robert

[Alextsu]

Thanks for comment, Robert.
I saw that You've been using the Jensen VB-1BB IsoMax Isolator transformer in Your test setup.
What is the purpose of using it, when You say that we do not need an injection transformer because the Cleverscope has an isolation function generator?
What is the main function of this particular transformer when working with FRA?   

[rbola35618]

Hi Alexey,

Those are very good questions and I might do a follow up video to clarify those questions.

A year or so ago I approached Bart in implementing an FRA feature into the Cleverscope. He had already been able to do frequency response bode plots on passive components. I asked him to try it on a power supply and I advised him to use an injection transformer to isolate the function generator from the power supply voltage. So he used a Jenson transformer. We got good results at high frequency about 100Hz but the lower frequency around 1 to 10 Hz were not too accurate. Some colleague of mine advice Bart that if he could design an isolated function generator, then we could do away with the injection transformer and greatly improve the low frequency response of the Cleverscope. About 3 months later, Bart came out with the isolated function generator. I bought the first isolated function generator. So this was a great improvement that was implemented.

The second big improvement was adding the ability to reduce the amplitude of the function generator as the frequency is swept to higher frequencies. The problem that arises is that at low frequency the power supplies generally have a lot of gain. And since you are injecting a signal in the feedback path by means of a 10 ohm resistor, the generator is connected to across the 10 ohm resistor which means that you need an isolation transformer or an isolated function generator. The probes of the Cleverscope are then connected across the 10 ohms resistor i.e.  Channel 1 to the high side and channel 2 to the low side of the resistor. At low frequency around 1 to 10Hz, because of the high gain in the power supply, the injected signal gets greatly attenuated. So you must inject as much signal as possible without saturating the power supplies error amp. Now as the frequency is swept to higher frequencies, the gain of the power supply will start to drop and you do not need as much injection signal from the function generator. In fact, if you do not lower the signal, it will start to saturate the power supplies' error amp. So the need to be able to reduce the injected signal is important.

Bart implemented this by making a table where you can fill the frequency and the amount of amplitude signal for the function generator to put out. This second improvement really helps in getting a good loop response.

I might do a detailed follow up video and explain that the Cleverscope is the only FRA in the market that I know of that you do not need an injection transformer.

Questions and comments can be posted here or sent to rbola35618@aol.com

Robert