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51
Test Equipment / Re: Using a AWG and a Scope -> ADC inaccuracy?
« Last post by HendriXML on Today at 06:54:27 am »
Here're the graphs of different symmetries: the time's are different, the Y values exactly the same.

I don't think its a dac issue anymore. It drops with a offset and I don't thnk the AWG has an extra dac for offsetting, but I might be wrong.

My guess would be that it is an "calculation error", however if the ramp was calculated at the AWG the vertical position was likely to change as well doing changes in the symmetry of it. I think it uses an arbitrary wave, which is scaled and has an offset, played at a certain sample rate(?). The wave sample data would then contain the glitch.

The error might well be that there a lot of samples are played double. Slopes up have namely a sudden drop, and slope downs have a sudden rise at the same level (at 50% symmetry). It might also be the same sample data but played in reverse for going down.

For me it is time to enter the territory of creating my own ramp and upload that and see what will happen.

However the documentation is sparse / non existing. I know of the wave editor that can be downloaded, but I'd like to create my own binary file. Trust is good control is better.

So does anybody know if there is some documentation on the file format?
52
I'm afraid I don't understand what you mean by  "sampling gate".  Would you mind providing a more complete description?  Both of my current units are covered with heat shrink tubing for mechanical and ESD protection.  IIRC it's a clock chip, MCU w/ USB interface and the laser driver plus the obligatory passives.

My understanding of the circuit is the 10 MHz clock is driving the the modulation input of the laser driver which dumps the output straight into the connector via a blocking capacitor. The Maxim part provides the slew rate for the sharp edge.  The MCU varies a digital pot to set the output voltage.  But that's only a rough guess.  I've never spent any time analyzing it.  It is so much faster than the 1.5 ns unit I built 30 years ago it's not even funny.

I've got a pair with 1 MHz clocks in place of the 10 MHz on order which makes them more useful for general TDR work.
53
General Chat / Re: What did you buy today? Post your latest purchase!
« Last post by blueskull on Today at 06:53:21 am »
Noctua?

2 Noctua 120mm fans running at 75% duty cycle for cooling all PXI cards, 1 Noctua 60mm fan for cooling the PSU, 1 Noctua 60mm fan for cooling the scope module.
ATM the two 60mm fans are running at 100% duty cycle, but I will dumb them a bit down with a resistor for each. Too bad they don't have PWM support.

I used a PSoC board to tap into the SMBus of the chassis, and I can control the 120mm fan speed in a home brew software.
The fan project turned out to be a fun project. The original 120mm fans were very noisy, and anyway one was dead on arrival, so I replaced both.
Since last time I sold my desktop PC part by part, I had some leftovers, which include 2 Noctua 120mm fans, and I finally found a use for them.

The fan controller spits a fake tachometer output to prevent the chassis from powering off automatically (the Noctua fans' RPM is not enough), and it reads in the real tach output from the fans.
If the real tach falls below certain value, it stops the fake tach output to allow system to be powered off automatically to prevent over heating.

I then added I2C support to set RPM protection threshold and speed for the 120mm fans, and I am going to add close loop control based on temperature, tach input and PWM output.
Simple 2 loop system, with the outer loop being an inverse P controller, regulating reference RPM based on temperature, and the inner loop being a PI controller, regulating PWM based on RPM input and RPM reference from the outer loop.

I finally had a chance to use my full bag of leftover LMT01 sensors as a bonus.
54
Thanks, it was fun.
I Added platform to the bottom.

Is one needed on the top for the machine?
Or does it mount directly to the top rails?
55
The conclusions in the video may be too fast.  It may still be just marketing / fake phases, but without actually looking at the board, it could still be true 8 phases.  As Warper showed with the picture, there are actual chips to double the phases, possibly combined with gate drive. So there is a very real option to use a 4 phase controller (running at twice the speed) and use 4 phase doubling gate drivers to get 8 real phases.

Those MOSFET chips sometimes have more than one MOSFET in a case - so the high side switch could actually contain two MOSFETs. Those are used only with a smaller duty cycle and thus produce less heat than the low side FETs. So one could get away with the 2 FETs in one case here.

So without really looking at the chips and MOSFETs it's a premature conclusion.
Did you actually watch the video? All of that is completely in parallel - mosfets, inductors. And particular controller chip discussed in the video cannot be used with doublers.
56
Test Equipment / Re: rise time
« Last post by ruggb on Today at 06:44:20 am »
new (last month) 1054Z with all upgrades and SP4 firmware.
When viewing the cal signal - as I change the time base, the displayed rise time changes.
The signal does not change so why does the displayed rise time change?

Because all calculations on a DS1054Z are done using the "on screen" data. You get most accurate numbers when you zoom in.
Thanks, so for sample shown the 3.00┬Ás is the closest, except that is most affected by the sample rate so it varies a lot
If the sample rate is 1Gs/S, what variation should I expect? It seems like it varies more that the sample rate would indicate. What else affects it?


57
Test Equipment / Re: Test Equipment Anonymous (TEA) group therapy thread
« Last post by wch on Today at 06:43:06 am »
You know you need to have one now.



arrghhh... i hate you! i've been wandering around for the last six days looking for a bargain 53310A, have a e-stack of manuals, and a saved ebay search. do i need one? of course not! but i didn't need the TDS420A and that's in my basement, next to my bench this morning, too (that's another story...)   |O

hey, i have an idea!  wanna trade one of yours for an oscilloscope? i have a lot of oscilloscopes right now.     ;D
58
Metrology / Re: Getting very low temperatures with TECs
« Last post by David Hess on Today at 06:41:14 am »
Stacking TECs absolutely works and is necessary for larger temperature drops but quickly reaches diminishing returns.  Careful consideration of insulation and condensation needs to be made.
59
The conclusions in the video may be too fast.  It may still be just marketing / fake phases, but without actually looking at the board, it could still be true 8 phases.  As Warper showed with the picture, there are actual chips to double the phases, possibly combined with gate drive. So there is a very real option to use a 4 phase controller (running at twice the speed) and use 4 phase doubling gate drivers to get 8 real phases.

Those MOSFET chips sometimes have more than one MOSFET in a case - so the high side switch could actually contain two MOSFETs. Those are used only with a smaller duty cycle and thus produce less heat than the low side FETs. So one could get away with the 2 FETs in one case here.

So without really looking at the chips and MOSFETs it's a premature conclusion.
60
Beginners / Re: Best Oscilloscope for complete beginner?
« Last post by Gyro on Today at 06:36:20 am »
I'm not sure what to think about a USB scope.  Sure, my AD2 is USB based and the UI isn't horrible.  I don't know how the VDS1022I UI works.  I watched a short video but I can't say I was impressed.  So, in the near future, I'll buy one just to test it out.  They're cheap enough and I have an application so why not?

Operation becomes a lot easier once you start using the, mostly undocumented, shortcuts.  ;)

http://www.eevblog.com/forum/testgear/owon-vds1022i-quick-teardown-(versus-the-hantek-6022be)/msg827103/#msg827103

Don't forget to expand the image, which highlights the items numbered in the list.
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