budget but still reasonable PC USB scope with isolation - Page 1
Forum section: electronics / testgear

author: deandob
author_rank: Newbie
timestamp: December 23, 2014, 11:57:04 pm
content: Hi,My Hantek DSO-2100 gave up the ghost after too many shorts to earth while debugging a power over Ethernet solution (48v) as it isn't isolated, and after a couple of years working with crappy to use software that won't install on x64 (so have use a virtual machine to run in 32bit), noise on CH1 etc. its time to get better more up to date scope. I'm a hobbyist with occasional use so don't have a lot of budget (below USD$200 if possible) and definitely want a USB scope as I have a PC on my workbench and don't want to use extra space (and money) for dedicated scope, and like the versatility of using a PC for measuring (eg. storing snapshots for comparison, playback etc.). I will also be doing a number of PCBs with power over Ethernet with a non isolated design which means a non isolated scope is a problem (yes, I could use a laptop on battery but would prefer not to have the extra bother of recharging, separate screen and so on).There are several reasonable scopes in this price range but the only isolated one I can find that has modern and functional software (x64 support on Win8, at least 100M sample rate, usable UI, good basic functionality like record, snapshot, spectrum analyser, scroll in the time domain) is the OWON VDS1022L ($140 AUD on eBay). OWON seem like a reasonable manufacturer but there is limited info/reviews about their USB scopes on the 'net.Having spent several hours on this website and others I can't locate anything else suitable in the price range. Do I have any other options? Thanks for the input.

author: zapta
author_rank: Super Contributor
timestamp: December 24, 2014, 03:03:49 am
content: What kind of voltage levels do you need to isolate? For low voltages one option is to use a non grounded computer, for example a notebook (running on battery or an isolated power brick). Not suitable for non safe voltages.

author: deandob
author_rank: Newbie
timestamp: December 24, 2014, 03:40:23 am
content: Up to 56v for Power over Ethernet (PoE), and the switcher design is non isolated with output earth at -53v so I can't measure voltages due to the ground reference of the probe and the PoE switch I'm using is earth referenced as well. Have tried and got lots of sparks and dead ICs.....I will need a bandwidth of about 25Mhz (micro clock frequency). The OWON VDS1022L looks ideal although its memory buffer is only 5K (more bandwidth would be good but it does sinx/x interpolation which will be sufficient to measure clocks).

author: electr_peter
author_rank: Unknown
timestamp: December 24, 2014, 01:33:15 pm
content: You can try using USB scope with USB isolator. USB isolators based based on AD ADUM1200 work well. Isolation is up to 2.5kV or 5kV depending on a device.There are few caveats with USB isolation:they can only provide USB low-speed (1.5 Mbit/s) or full-speed(12 Mbit/s) (no high-speed 480Mbits/s). Depends on your scope requirements. Newer USB scopes probably use higher speedsUSB isolators provide only 400mA isolated power. There are models with external power input (external powermustbe isolated).Other option - buy expensive USB->USB fibre-optic cable. These should support USB 3.0/3.1. They have been introduced recently. Downsides - high price and you must provide separate isolated supply.By the way, these USB isolators do not solve scope channel to channel isolation problem. Grounds of all probes are at the same potential.

author: deandob
author_rank: Newbie
timestamp: December 25, 2014, 01:12:25 am
content: Thanks.USB isolators are an option but an extra hassle / cost. Will look at buying the OWON VDS1022L USB scope with built in isolation, it has all the features I'm looking for except a small buffer at 5K. I assume as the data is being streamed to the PC for display that the software can do the buffering (to move back in time to analyse a digital waveform) so the on board buffer shouldn't be a restriction.