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| Gw Instek GDS2204E (200MHz 4 channel DSO) review |
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| nctnico:
--- Quote from: tautech on February 19, 2018, 11:47:42 pm --- --- Quote from: nctnico on February 19, 2018, 08:26:57 pm ---That depends entirely on how the input circuit is designed and it is not 200x but 5x (40V/8V full display range @ 1V/div = 5x). If the oscilloscope allows a large offset then the input circuitry should be designed to handle a signal which swings between the maxima of the offset. It seems the Rigol has a design flaw and thus has overdrive problems. --- End quote --- Yep, the devil is in the detail. For the new Siglent X-E series: Offset ranges 1x input. 500uV~118mV/div: ±2V 120mV~1.18V/div: ±20V 1.2V~10V: ±200V/div 2V/div will give sufficient offset for DougM's needs and using the minor divisions ~250mV resolution. --- End quote --- That only works if the Siglent doesn't have overdrive recovery problems just like the Rigol. Designing for a DC offset is easier than for a large signal swings. |
| DougM:
Even though my excuse for getting a better 'scope for home use has been undermined by finding that my Rigol works a lot better at 1x probe setting, I've read this entire thread and am being sorely tempted to get one of these scopes! Thanks for the detailed review and discussion. Doug |
| 2N3055:
--- Quote from: tautech on February 19, 2018, 11:47:42 pm --- --- Quote from: nctnico on February 19, 2018, 08:26:57 pm --- --- Quote from: 2N3055 on February 19, 2018, 07:27:24 pm ---For DS1000Z: Offset Range (Probe ratio is 1X) 1 mV/div to 499 mV/div: ±2 V 500 mV/div to 10 V/div: ±100 V As far as I could see, DougM wants to look at part of 40V P-P signal at better than 1V/DIV or less.. No digital scope I know of will have dynamic reserve of 200x of full screen sensitivity... And probably only +-8 to 10 DIVS... --- End quote --- That depends entirely on how the input circuit is designed and it is not 200x but 5x (40V/8V full display range @ 1V/div = 5x). If the oscilloscope allows a large offset then the input circuitry should be designed to handle a signal which swings between the maxima of the offset. It seems the Rigol has a design flaw and thus has overdrive problems. --- End quote --- Yep, the devil is in the detail. For the new Siglent X-E series: Offset ranges 1x input. 500uV~118mV/div: ±2V 120mV~1.18V/div: ±20V 1.2V~10V: ±200V/div 2V/div will give sufficient offset for DougM's needs and using the minor divisions ~250mV resolution. --- End quote --- Tautech, thanks for the info.. It is not about offset. That was mentioned in passing, not relevant for original question. It is a good reminder to the fact that all scopes are different, though.. For instance from 500mV to 1.2V Rigol has 100V offset compared to Siglent 20V. If that is of significance to anybody... But that is only relevant if you have a small AC component riding on top of a large DC component. In which case you can use AC coupling too. Most of the time, DC offset is simply used to move channels vertically on screen for visual separation. Problem is something else. If you have 10 vertical DIVs on screen... you put in 40V AC P-P, and put it on 5V/div you see nice +/-4 divs signal. Then you realize a small something, maybe 100mV anomaly at zero cross. So, you put it on 50mV/div so anomaly would be at least +/-1 div (2 div P-P) vertically so you can have a better look. At this point, full screen dynamic range of input is +/-500 mV (1V P-P).. You are overdriving it 40X... On top and bottom.. not where you are looking. Old analog CRT scopes had different circuitry, working on much higher internal voltages (even full solid state integrated ones). They had to actuate electrostatic plates on CRT tube. That gave them much larger linear dynamic range and also many times a more graceful clipping and recovery... They were better at this. Regards, Sinisa |
| rhb:
Heating of the input attenutator network, especially the capacitors, is a big deal. Someone at Tektronix derived an analytic solution which was held as a closely guarded trade secret for a long time. There was a reason "scope" and "Tektronix" were synonymous for a long time. I have an article about it in a book somewhere, but it was not in the ones by Jim Williams and Bob Pease where I expected to find it and my library is a bit too large to justify a search. As I recall it was a Bessel series expansion. I remember thinking when I read it the article what a tremendous amount of work (i.e. months) it must have been to derive. Each setting in the attenuator network is expecting a particular voltage range. So if you drop off the higher voltage attenuators the remaining stages get severely overdriven. Unlike analog scopes which had to generate the deflection plate voltages, a DSO reduces the voltage before feeding the signal to the ADC if it is above the ADC range. An amplifier is only needed for voltages below the ADC range and to buffer the input. Sadly despite the fact that component level repair would be much easier on a single board SMD DSO than something like a Tek 465, the tradition of providing proper service information to the user has died. As a consequence, few people are aware of the details of DSO circuit designs. Getting a believable presentation of something like high frequency ringing after a 40 V step is not easy. The only way I can think of to do that would be to apply an external bias, AC couple the scope and use an external comparator to switch the signal on and off. Otherwise the opposite swing would cause heating and non-linearity. This would be rather difficult to implement if the step had a fast rise time. |
| seronday:
For anyone who may be interested, it is possible to install a license file in the GDS-2000E series to upgrade the bandwidth. I have recently used an experimental license file generator created for the GDS-1000B series by EEVblog member, wgoeo , to upgrade a GDS-2074E (70Mhz) to 200Mhz bandwidth. The Info on the license file generator and how to use it, is in this thread :- https://www.eevblog.com/forum/testgear/possible-gw-instek-gds-1000b-hack/ When the license file is installed, an additional entry appears on the " Utility - System - System Info " screen. Also a new file called " OptionConf ", is created in the GDS-2000E file system under /home/dso . The option license can be removed by deleting or renaming this file. Note that in the current FW ver 1.34, ssh access has been disabled, so it is necessary to install an earlier FW version to gain access to the internal file system. The attachments show the additional info on the System Info screen and the frequency response before and after the 200Mhz license file installation. Regards |
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