Running a scope from an inverter - Page 1
Forum section: electronics / testgear

author: G7PSK
author_rank: Super Contributor
timestamp: May 23, 2013, 06:11:48 pm
content: I need to run a scope in the field and by that I mean a field. Would it be safe for the scope to run it from a small inverter, the inverter produces square wave power my scope has a switch mode power supply.https://www.eevblog.com/forum/Smileys/default/confused0024.gif

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 23, 2013, 06:18:53 pm
content: I'm not sure. The SMPS itself should have no problem dealing with a square wave, after all after the bridge rectifier it will look the same. But if there is a lot of high frequency stuff (a real nice square wave) would it be able to cook the input filter? I guess it depends, if the input of the SMPS starts with a choke it would not do much harm.Well, that wasn't really helpful

author: andrewkirkby
author_rank: Contributor
timestamp: May 23, 2013, 06:19:48 pm
content: I'd be careful if you're mains earth referenced.. Might need to shove a ground spike into the field and tether that in to the inverters earthing point.On the side of the square waves I'm not sure.. I guess a digital scope's probably more likely not to be affected but it would really depend on the circumstances..

author: Skimask
author_rank: Super Contributor
timestamp: May 23, 2013, 06:21:08 pm
content: People much smarter than I on this subject will chime in with better, more technical info, but...I ran my Tek 2246A in my truck, with the truck running, off the cigarette lighter, thru a cheap 700 watt inverter. Bad, ugly 150V pk-pk square wave output.Other than a bit of faint whining from the 'scope's PSU, it seemed to work fine.

author: andrewkirkby
author_rank: Contributor
timestamp: May 23, 2013, 06:22:45 pm
content: This is one of those cases where when you upgraded to the latest model if you kept the old one it would be it's time to play huh..Someone else posted about keeping his rigol 1052e the other night.. Now's it's timeI'd offer to try mine and run some tests in my car but I'm on a sine wave inverter..I guess you got a really hot square wave test source too.. but again, watch out for that mains earth reference!!

author: kfitch42
author_rank: Frequent Contributor
timestamp: May 23, 2013, 06:42:51 pm
content: Do you have budget for a new scope? There are some actual battery powered scopes out there, e.g. the Fluke ScopeMeter Dave played with a while back.Or a USB scope plus a laptop?

author: Unknown
author_rank: Unknown
timestamp: May 23, 2013, 08:03:57 pm
content: I wouldn't be too worried about the square wave, assuming the scope uses a SMPS (impossible to tell since the scope brand and model were thoughtfully omitted, but very likely if it was made in the past ~twenty years). I would be worried about grounding. A grounded scope used in the proximity of grounded metal surfaces (eg. a desktop computer) is safe, since it's always at ground level. A floating scope used in the absence of any grounded surfaces is somewhat safe, since no significant current can flow from a person to ground. A floating scope in the presence of grounded equipment is a safety hazard. Does the inverter provide a solid connection to earth?Manuals of battery powered scopes without isolated channels will usually state that you should run a separate grounding wire when used with voltages above 30 V or so. If you clip the ground lead of your scope probe to something at a dangerous potential to ground, then the floating scope also gets raised to this voltage. Touching one of the BNC jacks, USB ports and even poorly insulated knobs can shock you.

author: G7PSK
author_rank: Super Contributor
timestamp: May 23, 2013, 09:21:08 pm
content: What I will be testing is a power plant that is running of grid, and cant easily be moved, I could take a portable gen-set with me that way I would be sure. The scope is a 2004 Iwatsu and has a swps. What I aught to do is get a portable scope but it is not usual for me to have to work in the field as I can normally drag the stuff to the workshop but this one is both big (175KVA) and 3 miles down a muddy track.

author: nctnico
author_rank: Super Contributor
timestamp: May 23, 2013, 11:22:55 pm
content: It will probably run fine as long as you don't run stuff with a motor in it from the same inverter. A motor can induce spikes and the inverter won't be able to dissipate those as good as the real mains does. Perhaps you should put a surge protector between the scope and the inverter just to make sure.

author: G7PSK
author_rank: Super Contributor
timestamp: May 24, 2013, 09:15:56 am
content: The problem is solved now without any testing required. All down to thick farmers. What was happening was computer controlled ventilation was shutting down in chicken sheds, they had decided to install a Hydrovane compressor which they would turn on and off as required to blow down equipment (chicken sheds are very dusty) in the past they had been using a diesel driven one but some one had decided that an electric one with a 30 hp motor would be a good idea, when they turned the compressor on there is big enough blip in the power to cause the computer to drop out, I could see the lights dim when they turned the thing on. Any way a couple of ups systems solve the problem without having to look any further or upgrade the genset. I dont have to do any work and can still send my bill in, can't be bad.