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SDS800X HD Actual Use Cases

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mawyatt:

--- Quote from: joeqsmith on May 03, 2024, 05:08:14 pm ---Plan to buy a new low end one at some point just to try out.  The 800 has a smaller display than my tablet.  It's difficult anymore to see these small screens without glasses.   Doesn't appear the 800 supports an external monitor as well.   Does look like a nice scope otherwise and it's certainly affordable.

--- End quote ---

We are 76 and bad eyes (cataracts and such), but can read the DSO reasonably well. The remote Web server works really well and isn't too slow and we use this often.

Best,

joeqsmith:
Maybe tszaboo will make an attempt at the PDN project. 

Another subject that had recently came up again was measuring SRF of an inductor.  I show measuring it with the cheap VNA but then also with a scope.  Again a pretty good actual use case for this particular scope.  Even if you can't drive a sharp edge, you can certainly square it up easy enough.  Your only dealing with a single component and much easier to setup and measure.   

https://www.eevblog.com/forum/beginners/measuring-the-self-resonant-frequency-of-an-inductor/msg5112405/#msg5112405

I'll see if I can find a video review showing that remote interface.   

mawyatt:
Another use for this DSO and the Bode Function is for regulator PSRR measurements. This is a measure of the regulators ability to attenuate unwanted signals/fluctuations from the input to the output.

We have a couple popular +-5 volt linear regulators, the 78L05 and 79L05 respectively.

The setup is rather simple with a series R (10 ohms) for the input power source and shunt C (0.1uF) for stability connected to the regulator input. Also a larger coupling C (100uF) from the regulator input to the Bode Signal source AWG output, this C provides DC isolation for the AWG. One could also use a coupling transformer common for use in closed loop measurements, but pay attention to the DC thru current as it can saturate the transformer core.

The regulator output is loaded with a shunt R (1K) and shunt C (0.1uF) for stability.

Bode connections are CH1 to the Regulator Input and CH2 to the Regulator Output. This will produce a dB ratio of output to input voltage and thus a negative dB representation. PSRR is generally specified as a + dB term, so one can swap the Bode inputs either physically or thru the Bode Configuration if necessary, however we prefer the negative connotation as this indicates an output less than input more of a Gain type display.

Anyway, here's couple plots showing the 78L05 (+5V) #2 and 79L05 (-5V) #3 PSRR. Note the inferior rejection of the negative 79L05 wrt the positive 78L05, both setups were identical except for polarity. The "response peaks" are partially attributed to setup (Protoboard), altho the 79L05 still appears worse in that respect.

For those interested the PSRR is influenced by input-output voltage differential and load current, so one could create a "family" of curves if desired.

Edit: Added a 78L15 #4 and 79L12 #5.

Best

mawyatt:
Now that we've got the Regulator PSRR, how about taking a look at the Regulator Output Impedance Z as a function of Frequency. We can apply the Bode function for this as well!!

Configure the Regulator setup with decoupling C on Input and Output, use a large value (100uF) for the Input and small for the Output (0.1uF) so we can view the Regulator Output Z as a function of Frequency.

Attached the AWG output to the load Resistor (1K) normal Ground end and DSO CH1 to same end, then DSO CH2 to Regulator Output which connects to the load R.

If we call the AWG output as V2 and the Regulator Output as V1, then:

Z (Regulator Output Impedance) = V1/I, where I is the R load current.

I = (V2-V1)/R

Z = V1/((V2-V1)/R), or R(V1/(V2-V1))

If V1 is << V2, implying R is >> Z, then,

Z ~ R(V1/V2)

Since Bode is in dB, and Y axis is 20Log(V1/V2)

Then Z is R* 10^(Bode Display)/20

Does it work??

Yep sure does :-+

Here's a plot #6 of a 78L05 output Z using a 1K load. Just add 20Log R (60dB) to Y axis, and then it's in dB ohms.

So at 100Hz the 78L05 Output Z is 13.8 milliohms, and 69.5 milliohms at 100KHz. Note the inductive nature (+ Slope) of the output Z beginning at ~10KHz.

Plot #7 is the 79L05 negative Regulator, 11.5 milliohms at 100Hz and 4 ohms at 100KHz  :o

Anyway, this seems like another useful capability of these new "Entry Level" DSOs!!

Best,

Performa01:

--- Quote from: mawyatt on May 14, 2024, 06:01:37 pm ---Since Bode is in dB, and Y axis is 20Log(V1/V2)

--- End quote ---

It is worth mentioning that Bode Plot doesn't have to be in dB. It can also use Vpp and Vrms.

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