| Products > Test Equipment |
| SainSmart DDS120 & DDS140 USB Oscilloscope |
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| doctormord:
Hmm, no AD adc anymore, but a chinese "pin compatible" MXT2088. |
| bianchifan:
--- Quote from: doctormord on February 17, 2016, 11:44:46 am ---Hmm, no AD adc anymore, but a chinese "pin compatible" MXT2088. --- End quote --- The only datas I could find are telling 8bit ADcv 100MSPS, 90mW 1Vpp..I cannot read chinese and I'm too lazy translating those fuc...datasheets via google. I do not think it causes the told probs. |
| doctormord:
Well, they state +-500mV FS while the AD is +-512mV. Maybe a translation error as most of their data is same as AD, even in the order. For the voltage error have a look at the gain stage resistors. If the error is same in percentage for different ranges, I'd check the ref voltage/s at the ADC. Maybe the MXT2088 isn't that linear at the top end. |
| bianchifan:
--- Quote from: doctormord on February 17, 2016, 12:26:04 pm ---For the voltage error have a look at the gain stage resistors. If the error is same in percentage for different ranges, I'd check the ref voltage/s at the ADC. Maybe the MXT2088 isn't that linear at the top end. --- End quote --- I did a few quick checks only, all seemed ok. ON Sainsmart's HP I found an older version of DDS140.exe (v 1.2) inm Analyzer/Generator sections offered as The Newest Version ;) 1. It displays 16 MHz same known shit but it displays. 2. Slew rate / steep curves same bullshit, even 100 Hz rectangles show rounded edges. 3. Loupe same crap, use with care, no side shifts 4. No more "Out of Range" with 5V, all signals were shown and sometimes they were triggered too. With AC selected, Voltage is fine, 4.93 V differed between 4.89 and 4.97 V, triggerpoint is the middle vertical line. Rising/falling seems fine, trigger level is a little mystery, only no trigger was working. Zero adjustment has an offset of .5V, thumb ruled. With DC selected I didn't notice any "out Of Range" too. Depending on the selected V/div it was too high, i.e. 5.8V in 2V/div and 5.6V in 1V/div thumb ruled instead of 4.93V. Rising/falling seems fine, trigger level is absolutely mystery, maybe for selecting the voltage area, a signal have to cover completely. With the "T"-LIne you can mark an area froom Zero to "T", all curves staying between these lines are displayed, "normal" and "single" will do. |
| doctormord:
So you'll check the resistor values at the range switch "CD40xx", maybe they aren't in the 1% or better range. You may also check if the voltage levels are changing vs temperature. As far as I remember the code, there's no 2 point calibration at all, just offset calibration for the zero line. |
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