Best way to build HV probe/divider - Page 1
Forum section: electronics / testgear

author: 001
author_rank: Super Contributor
timestamp: December 16, 2018, 02:01:30 pm
content: Hi!Now I use simple 990M resistor in series with my DMM (input impedance is 10М) to measure 4kV voltageWhat way will be the best? I`m confused with a fact what DMM input impedance is a part of voltage divider. It looks unsafe for me

author: med6753
author_rank: Super Contributor
timestamp: December 16, 2018, 02:32:03 pm
content: Two words: DO NOT.If you value your life and your equipment I don't recommend trying to build up your own high voltage probe.If you REALLY have the need to measure high voltage spend the money on suitable high voltage probe with the characteristics to match the DMM you are using.Edit, here's an example. B&K Precision PR-28 suitable for 10MEG input DMM's.

author: tggzzz
author_rank: Super Contributor
timestamp: December 16, 2018, 03:35:30 pm
content: I hope this has nothing to do withatopic you started yesterdayhttps://www.eevblog.com/forum/testgear/where-i-can-read-iec-60601-standard/msg2041996/#msg2041996which is about medical equipment standards.001, you are getting a reputation, e.g.https://www.eevblog.com/forum/testgear/what-this-unit-do/msg2040466/#msg2040466to wit:Quote from: coromonadalix on December 14, 2018, 10:13:10 pm

author: joeqsmith
author_rank: Super Contributor
timestamp: December 16, 2018, 05:37:33 pm
content: Quote from: med6753 on December 16, 2018, 02:32:03 pmHigh voltage does not have to equal death sentence. I think my piezo gas grill starter measured over 10KV and I could take a direct hit from it all day long and not die. Still, not a bad stance to take. We have no idea what our friend who is 65 year old, living in antarctica, using words like suck, owning several Flukes and can't read their displays, is thinking. I am not not at all surprised that they are confused. It may be the first thing they have posted that makes some sense.QuoteIt depends what the requirements are. I posted that link the other day on making attenuators. Perhaps the video was too complex or long for you to follow?1) Wideband 1KV 100X voltage probes2) HV current probe used to look at ESD and other fast events3) Wideband 40KV voltage probeAlso towards right a discharge probe for the generators (LED is active above 20V or so). The is used to short out the generators when I am working on the setup. >20J at over a KV could be lethal.

author: james_s
author_rank: Super Contributor
timestamp: December 16, 2018, 05:47:42 pm
content: Building a reasonably safe HV probe is not rocket science, however it's hard to justify the effort of doing so when you can buy proper HV probes on the used market for reasonable prices. I don't remember what I paid for my Fluke HV probe but I think it was only about $50.

author: David Hess
author_rank: Super Contributor
timestamp: December 16, 2018, 05:51:54 pm
content: Quote from: 001 on December 16, 2018, 02:01:30 pmIt *is* unsafe and most autoranging DMMs have variable input resistance compromising accuracy.For safety, a shunt should be included as part of the probe.

author: Wolfgang
author_rank: Super Contributor
timestamp: December 16, 2018, 11:24:02 pm
content: Hi,Frankly, when its only 4kV I would buy one instead of building one. The major problem with homebrew HV probes is proper mechanics and insulation. For a few ten € you can get very decent used 4kV probe from Keysight or Tektronix.Of course its possible, but its quite some effort if it needs to be a bit wideband.Remember the old HV mantra: Your first error is your last error.Have fun, play safeWolfgang

author: james_s
author_rank: Super Contributor
timestamp: December 17, 2018, 01:21:55 am
content: Then again, 4kV is not too hard to contain, it's pretty easy to use a PVC tube with end caps or something of that sort as a housing. When it comes to hobby HV stuff the apparatus is often more dangerous than the test equipment. Either way, be careful.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 17, 2018, 02:04:22 am
content: You have to put high voltage resistors and dividers and provide very good insulation ....... not woth it if you play with your security and your life ?But if you're really sure of what youre doing ... well i did told myself that one time,, forgot to properly short and discharge an 35kv tv tube screen, my hand were a little moist, i saw a beautiful arc going into my hand, dropped everything on the floor, my heart did / was going bezerk for an hour.

author: Kean
author_rank: Unknown
timestamp: December 17, 2018, 11:04:15 am
content: OP's location is marked as Antarctica. While I strongly suspect that may not be real, it would explain his difficulty in just buying something off the shelf...

author: Hydron
author_rank: Super Contributor
timestamp: December 17, 2018, 05:23:49 pm
content: Maybe he left his kit bag behind in Christchurch and needs to probe a IceCube photomultiplier tube?