Products > Test Equipment
Siglent SDS1x04X-E BodePlot II (SFRA) features and testings
mrprecision:
I have send an e-Mail to my Siglent contact regarding the -200/+200 scaling problem. They had also fixed my other bugs I had.
rf-loop:
--- Quote from: mrprecision on November 15, 2020, 05:23:33 pm ---
--- Quote from: torquil on May 04, 2020, 10:49:53 pm ---I have a Siglent SDS1104X-E that I use together with an SDG1062X, and the Bode Plot II function is very nice! But there seems to be a limit so that the y-axis cannot go beyond values in [-200,200], which is a bit troubling when using the BPII for impedance measurements with a linear y-scale.
I have made a small connection box for easily connecting everything required for an impedance measurement. One of the items I tested was a 3:1 transformer with a 100R load, so the input impedance will be beyond 200 Ohm. To get the impedance I provide voltage and current measurements to the Bode Plot II system, and use the Vout/Vin display (Vin represents current for this measurement) and a linear display on the y-axis.
These measurements work as expected, but since the input impedance is beyond 200 Ohm for the transformer, the graph disappears outside the plot area. I am forced to either manipulate the probe multiplication factor or use a logarithmic scale. I know I can get the CSV, but it would be nice to have an immediate and correct plot.
Anyone here know if this has been reported? I do use the newest firmware versions.
--- End quote ---
I have tried it with my connection box. I found the option to set the y-axis linear. You are right, there are limit of +/-200. That is not very nice. If you activate the table of the values, you can see the correct values. I will report this to Siglent.
How is your connection boy set up? Do you have a photo or a schematic? I have the Scope and an SDG2xxx frequency generator, all Scope probes and the generator is connected to earth. How did you solve this problem?
--- End quote ---
Because I do not understand fully this setup (bolded in quote) I only can "blind" ask... is it possible to solve or help this situation so that also set BodePlot for this real used impedance instead of default 50ohm. This is also adjustable in BP!
mrprecision:
The problem is not because of the impedance measuring. It is a bug in the BodePlotII function.
For example, if you make a Bodeplot of an amplifier with a gain for example of 300 and use in the Bodeplot a linear y-axis scaling, you should see the gain of 300 in the diagram. But the Diagram is limited to a gain of -200 to +200, so the curve is outside the diagram. In the list table the values a shown correct. The limit of -200 and +200 should be eliminated and the auto scaling of the linear y-axis should be fixed. The logarithmic scaling works fine, maybe there are also limits.
So it is not a problem with the impedance measurement over the frequency, witch works fine. I only saw that problem there yet, because I had no amplifier with this gain. I still prefere the double logarithmic scaling, so capacitors for example are a straight line.
Maybe we could discuss here the adaption boxes for impedance measurements to optimize that.
mrprecision:
--- Quote from: mrprecision on November 16, 2020, 09:06:22 am ---The problem is not because of the impedance measuring. It is a bug in the BodePlotII function.
For example, if you make a Bodeplot of an amplifier with a gain for example of 300 and use in the Bodeplot a linear y-axis scaling, you should see the gain of 300 in the diagram. But the Diagram is limited to a gain of -200 to +200, so the curve is outside the diagram. In the list table the values a shown correct. The limit of -200 and +200 should be eliminated and the auto scaling of the linear y-axis should be fixed. The logarithmic scaling works fine, maybe there are also limits.
So it is not a problem with the impedance measurement over the frequency, witch works fine. I only saw that problem there yet, because I had no amplifier with this gain. I still prefere the double logarithmic scaling, so capacitors for example are a straight line.
Maybe we could discuss here the adaption boxes for impedance measurements to optimize that.
--- End quote ---
Maybe we could discuss here the adaption boxes for impedance measurements to optimize that?
graybeard:
--- Quote from: khutch004 on January 10, 2020, 05:10:20 pm ---For really-high-quality audio power amplifiers, a bode plot of the range 0.1 Hz to, say, 100 Hz will enable a designer to accurately predict the audibility of artifacts coming from attempts to limit the vlf range by steep slope high pass filtering of subsonics.
People building bass guitar amps and high pass filters for them are interested in evaluating the very low frequency response. They often use an HPF to prevent the cone excursions from exceeding safe limits if subsonic information appears at the amplifier inputs. Bass cabs often walk a fine line between being able to generate a high output level at 30 to 60 Hz and blowing up when presented with low frequency noise and often some help from the amp or a filter in front of the amp is needed.
A better question to ask is the 10Hz low limit arbitrary or is it driven some important cost or reliability concern?
If it was just an arbitrary limit then why NOT extend it as far as possible?
People building filters for some scientific applications will want to test at sub 10Hz frequencies. There may not be terribly many such people but again if the limit is arbitrary then it should be removed.
--- End quote ---
I suspect the 10 Hz low frequency limit is due to the low frequency roll-off of the AC coupling on the scope since it always changes to AC coupling for the bode plot function. The AC coupled low frequency roll off -3dB point is speced at ≤2 Hz. For gain flatness you want to be at least a decade above that.
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