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Trying to use frequency counter to read WFM/s from MSO5000. Need help.
ballsystemlord:
Hello,
Recently, Dave made a video about the KS HD3 oscilloscope and compared it to the R&S MXO 4 series. I wanted to replicate his test to see how my MSO5000 scope compares in it's WFM/s rate to the above two scopes. During my testing, I observed some odd behavior. I thought about asking how this works in the HD3 thread, but I didn't want to hijack the thread so I'm spinning up my own.
--- Quote ---
--- Quote ---@Dave (I said), I just thought about this, but doesn't the HD3's reading it's own trigger invalidate the WFM/s test?
Like, if the scope is in it's "dead time" it's neither reading the trigger pulse nor outputting it. Therefore, according to the scope, it's trigger rate is always 1M+ WFM/s.
Maybe I'm not understanding something?
--- End quote ---
I used the frequency counter function, not triggerign from it's own trigger output. (Dave replied.)
--- End quote ---
Now I setup my MSO500 to use it's own frequency counter. In the photo below, you can see my setup (I did try it with an official Tek 50 terminator. That doesn't change anything.) I get the result of 41.75Khz. According to my calibrated GW Instek 9061 DMM, that's dead wrong. The update rate is actually ~19Khz. I also got roughly the same result with an out-of-cal BK precision 391A. So this isn't an artifact of the GW Instek meter.
I tried turning the counter off and on, setting the scope back to default settings, and I found that the frequency that the scope reads is either the above 41.75Khz, or ~15Khz, seemingly randomly switching between the two. I tried turning channel 4 on, but that just resulted in the counter not working at all; even after turning off and then back on the frequency counter.
To be clear, I'm fully aware that the HD3 and the MSO5000 are totally different beasts. But I'm still really lost here as to why this isn't working on the MSO5000 but apparently works just fine on the HD3.
Can anyone explain what's going on?
Thanks!
PS: I'm happy to perform any further tests as you see fit to narrow down what's going on, provided it's within my capabilities to do so.
PPS: If it helps, the trigger output of the MSO5000 is 3.3v logic. With a 50ohm terminator attached the voltage falls so far that my GW Instek 9061 cannot read the frequency. It's capable of reading up to 1.2Mhz accurately (oscilloscope wave gen into DMM). It makes no difference if the terminator is feed-through or a 50ohm load attached to a BNC tee.
Someone:
You really need another scope to check the "trigger" (acquisition) out waveform. It is usually pluse trains with inconsistent frequency, that will confuse many "frequency" measurements, and unscrupulous manufacturers use the peak rate of the pulses as their spec.
ballsystemlord:
--- Quote from: Someone on September 22, 2024, 01:26:51 am ---You really need another scope to check the "trigger" (acquisition) out waveform. It is usually pluse trains with inconsistent frequency, that will confuse many "frequency" measurements, and unscrupulous manufacturers use the peak rate of the pulses as their spec.
--- End quote ---
When setting the "Gate time" of my DMM I did notice that. I've seen others, on YT, use dedicated frequency counters to do the same measurement I'm doing with my DMM. So, I assumed my DMM was good enough for the job.
Unfortunately, I have only one oscilloscope at this time. Although I could go for one of those really cheap handheld scopes from china, I think I'm better off waiting till I could afford better equipment.
Sensorcat:
Use the frequency measurement from the measurement menu instead. It offers several parameters to customize the measurement and address the issues you see with the counter. This includes the possibility to average, which is useful because you don't want the peak rate, as Someone pointed out. But it's definitely possible to measure this with the instrument itself. I have done that, at least for some instrument settings.
ballsystemlord:
--- Quote from: Sensorcat on September 22, 2024, 01:43:10 am ---Use the frequency measurement from the measurement menu instead. It offers several parameters to customize the measurement and address the issues you see with the counter. This includes the possibility to average, which is useful because you don't want the peak rate, as Someone pointed out. But it's definitely possible to measure this with the instrument itself. I have done that, at least for some instrument settings.
--- End quote ---
I tried what you suggested before, but thought I'd post a picture so you can see what happens. What happens is that I don't get any frequency reading at all.
I set the persistence to 1s, so you can see that what I'm getting is only part of the square wave. In the picture, I'm using the default/auto memory setting.
I tried changing the memory setting from 1Kpts through 100Mpts in increments of 10x per step with the hope of changing the update rate to something the scope could read. I also tried changing the span from 100ns to 50us, without effect (again, tried playing with the memory settings.) I also tried panning the span back and forth without effect.
I'm not trying to say that you're wrong, just that I can't imagine how to do this correctly, in the sense that I get a sane result, or in this case, any result.
EDIT: Forgot to attach photo.
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