| Products > Test Equipment |
| Measuring ~ 400V on oscope - 10:1 OK or differential probes ? |
| (1/5) > >> |
| TomKatt:
I need to work on an old tube based scope and want to use my modern Siglent SDS1104X-E to view some signals. The tube scope has +400VDC and -300VDC rails. My measurements would be from a rail to ground (0V / chassis ground that is earthed) and not rail to rail (potential 700VDC). So the max signal amplitude should not exceed 400VDC. Question - I note the SDS1104X-E specs maximum input at 400Vpk. Would using 10:1 probes be within spec, or should I use a my Micsig DP10007 10X/100X that is rated to 700Vpk ? I'd be looking for distortion in my readings and I know the Micsig probe doesn't have the greatest CMRR, so I'd probably get cleaner measurements using a normal 10:1 probe. Wouldn't the 10:1 probe reduce a 400VDC signal to 40VDC, which is safely within spec? Thanks! Edit - My 10X probes are ProbeMaster 4900 series, rated at 600VDC |
| KungFuJosh:
Your probes are rated 50% higher than your target voltage, you'll be fine. You only need to worry about the scope's voltage rating when your probes aren't voltage rated (for example, using coax cable instead of a probe). You can also get higher rated passive probes, they don't have to be differential probes. |
| TomKatt:
Thanks. I get the probe capability part, just want to ensure I don't blow up my nice Siglent by overloading the front end or something. Edit - technically, 10:1 probes are simple voltage dividers so the scope should only see 40VDC when probing 400VDC... If the voltage was a bit less I'd just give it a whirl but since I'm at the edge of the scopes rated input I wanted to ask more experienced folks here. |
| KungFuJosh:
Unless the probe has some kind of weird catastrophic failure, you only need to pay attention to the probe's voltage. I use ProbeMaster probes rated at 600V, and probe stuff in the 400V range with no issue (tube guitar amps mostly, and my tube tester/tracer). I also have a PR2000B 2kV probe, and a DP10013 diff probe, but those almost never get used. |
| bdunham7:
Two thoughts: 1.) A 10X probe will just barely work, I say that because the real limitation isn't the rated input voltage on the front of the scope, it's the lowest vertical gain setting (most V/div) which IIRC is 10 V/div. So a 40 volt signal is 4 divisions, anything larger and you'll have issues keeping the whole signal on the screen. I use a 100X probe in these situations, and depending on which 100X probe you use, this may have the additional benefit of reducing circuit loading. 2.) The voltage rating is one thing, but you have to watch for the frequency derating as well--and this may or may not be explicitly stated. At those voltages I'd stay under 100kHz unless you have a reliable derating graph or table. |
| Navigation |
| Message Index |
| Next page |