Power quality monitor -- cheap?

On a sunny day (Wed, 21 Feb 2007 12:13:59 -0800) it happened John E. wrote in :

A simple idea: Divide the main to .7V eff with 2 resistors. Feed into PC soundcard line input. Record a wave file at 8000 samples/second mono. Bit harddisk space should last a long time. When done enter recorded wave file in an audio editor, display waveform, and look for peaks, etc....

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Please! I h>On a sunny day (Wed, 21 Feb 2007 12:13:59 -0800) it happened John E.

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Otherwise its a good idea except for the safety issue. Get a step down transformer from "ma>On a sunny day (Wed, 21 Feb 2007 12:13:59 -0800) it happened John E.

NO! At least run the AC through a 120 - 12 volt step-down transformer first. Hooking AC directly to the input of a computer is a seriously bad idea.

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Interesting concept. I bet if you used a compressed format like MP3 the disk would last for a really long time. Any machine in the faster P1 or P11 class can compress on the fly.

I don't know of an inexpensive commercial solution for catching fast transients and harmonic distortion. The Fluke 189 will capture sags and surges if you set the log rate fast enough, and it will capture 250uS transients, although I don't recall how much it can do simultaneously. I have one, but I don't use it for that purpose. It stores 100 readings, and does have a com port for uploading data.

You might also consider a BMI 4800, generally available on eBay pretty cheap. It has a built-in printer which will print actual waveforms, and also had a communication option. It is old technology, and not the smallest physical package, but it does a good job on transients, and the price is right.

The other professional equipment that I use is definitely outside of your stated budget. You might start finding the Fluke 43 at a more reasonable price on eBay, since there are newer instruments now on the market. If you can get one, it works well for single-phase monitoring. It stores and displays locally, and can upload to a PC for further analysis.

The other option is to roll your own, as others have suggested. However, I will also emphasise isolation if you are connecting your PC to the power line!

Ben Miller

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Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com

Gaah, no! MP3 is a lossy compression--it would loose your spikes and dips! Just record it as-is... Disks are cheap.

And, yes, use an isolation transformer!

Ideal Industries has an interesting low cost product called the Voltage Performance Monitor. You cannot download data from it or see waveforms, but it does count events outside of the ITIC curve (update of the old CBEMA curve) and categorizes them based on type and severity. It is reasonably accurate in doing this characterization, not something that can be said of all meters, even more expensive ones.

Charles Perry P.E. Not an indorsement. I don't have a financial interest, etc, insert legal weasel words, whatever.

I'm not positive of this, but I believe some of the UPS systems that have cabled monitoring, i.e. hook to your computer via serial port or USB, will give a power line reading if queried. Don't ask me which ones. I know my TrippLite 1000VA unit has a front-panel display and I *suspect* it would tell the computer the line voltage if asked.

--
"Nowadays, security guys break the Mac every single day. Every single day,
they come out with a total exploit, your machine can be taken over totally.
I dare anybody to do that once a month on the Windows machine."
 -- Bill Gates, in an interview with Newsweek\'s Steven Levy

How about one of these?

Why should he?

It's the equivalent of use a "scope" probe to look at line voltage. The "danger" is at the probe tip but not at the end going to the scope.

There is a question of just how well a transformer will pass the transients. OTOH, without compensation it's possible that the "voltage divider" may not properly pass the transients. That's why scope probes were so expensive.

I do grant that a transformer makes it so that if you make a mistake (like forget to connect the "lower" resistor) you don't have a shock risk.

I have never done this.

I note that "they" now sell the equivalent of the input side of a sound card that's as big as one's thumb and plugs into the USB port.

Personally, I would like to be able to monitor start up current and voltage transients when my "heavy stuff" (heat pump and deep well water pump) starts up.

>

Fluke VR101S

JB

A cheap UPS? Mine can be queryed via a serial port and tells you line voltage and frequency (along with a lot of other things you probably don't care about).

Geoff.

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Now that you mention it, my PowerWare UPS does have this feature, and a program can record line conditions based on a polling interval. Probably nto the best solution however since I am sure short (single cycle) faults will be lost in this setup.

Another alternative is eBay. I see products like the Amprobe monitors (older, chart type) selling for about $100 or so. Hell, I'll sell mine for that!

On eBay:

and

both of which do what the OP wants. These units do require special chart paper which is not cheap, but are solid and dependable units.

Call the power company and see if they'll lend you one.

Good Luck! Rich

spikes

Right. It's only really good for trends. But sometimes faults follow trends. And it's a whole lot less data to process than, say, 600 Hz samples of line voltage over a week (362,880,000 samples to check).

--
"Nowadays, security guys break the Mac every single day. Every single day,
they come out with a total exploit, your machine can be taken over totally.
I dare anybody to do that once a month on the Windows machine."
 -- Bill Gates, in an interview with Newsweek\'s Steven Levy

No, it isn't. The designer of the scope will have at least contemplated what happens when you are examining a live circuit at 120 or 240 volts. Will the designer of the computer have done as much?

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Right! which reminds me some time back, I gave Helga some bad advice involving live electricity and a swimming pool. She hasn't posted since!

;-P

Homer J Simps>