Oscilloscope for Recording Transients

[Laplacian]

What is a decent resolution for recording transients created by closing in power factor correction capacitors; for example?

Also, what probes would best be used for connection? Voltage leads on a CT secondary, or clip on Hall-effect type probe?

I'm seeking a good hand-held type scope for troubleshooting nuisance trips and general power quality issues at one of our facilities. What bandwidth and sample rate would be best suited for power quality? Thanks in advance.

 

[jbartos]

Suggestions:
1. Resolution: Visit

http://www.laboratorytalk.com/news/gou/gou105.html

for: SVGA resolution

http://www.engineering.co.kr/test_homepage/main/main_frame/product/01_directory/pdf/DSeries.PDF

for: A/D resolution: 8bit .39%
2.
A probe type depends on an application and transients.
3.
Visit

http://www.tti-test.com/products-resale/tek/tek-ths700.htm

for:bandwidth, and harmonics up to 31st

http://www.ferret.com.au/articles/0d/0c01000d.asp100MHz

etc. for more info

 

[DougMSOE]

Been there, done that.
An oscillograph works the best but it is an analog type (read old) piece of equipment.
Astro-med has some great recorders that as well if not better than the old O-graph.

Digitally, a point every 10 to 100 micro-seconds. A digital oscilloscope should do the job, then dump it to Excel if you wish.
Suggest a Hall effect clamp on type. With some care it will provide accurate results.
I would be very careful with measuring the Vdrop on a CT. If it opens, your equipment is gone. Also you might inadvertantly cause a ground in the system.
I would look at the Fluke Scopes. They will hold up in some very bad environments. Mine is 100MHz

 

[ScottyUK]

Tektronix make a range of handheld 'scopes, one of which is designed for power engineering applications. They are more expensive than the Fluke-Philips offerings, but IMHO are a better product. HP, or Agilent as they now call themselves, and LeCroy are the only manufacturers who seriously rival Tektronix in the oscilloscope market. Neither HP nor LeCroy make a hand-held so far as I know. Fluke's products are good for the money, but fall short in the absolute performance stakes.

If you are measuring current, use a Tektronix AM503 series current probe and amplifier. The bandwidth is high enough not to matter (50MHz), and it will not introduce any phase error at frequencies of interest to a power engineer. Most CT's have lousy bandwidth and introduce phase and amplitude errors so don't use them unless you are backed in to a corner. The AM503 probes are expensive - rent one!

You could consider a Hall-effect probe from, as a suggestion, LEM-HEME. I have mixed feelings about these instruments. They are very good in the right environment, but I have also had some awful experiences with high dv/dt signals being capacitively coupled in to the output. Sometimes when a signal just looks 'wrong', you have to remember that the transducer isn't always blameless. The AM503 probes have never suffered this problem in my experience, but the absolute maximum ratings are just that. No tolerance, just a dead probe if you exceed the limit.

Your local instrument distributor should be able to get you a demo or loan instrument. See which feels best to you - much of value of an instrument is in the user interface, not the spec sheet.

 

[jbartos]

Suggestion: Visit

http://www.abletron.com/Oscilloscopes.htm

for an Oscilloscope selection and parameters

 

[IRstuff]

One factor to consider is how much waveform memory is available, particularly if the trigger signal is offset in time from the actual event.

TTFN

 

[ScottyUK]

IRstuff has picked up on very good point.

Have a really good play with the triggering facilities and make sure you can capture what you wish to see. Triggering on irregular waveforms and single-shot triggering was a nightmare with the early Philips Scopemeters (now part of Fluke). The later models are better. The Tek instruments were always good.