Power meter - Page 1
Forum section: electronics / testgear

author: NiaDebesis
author_rank: Frequent Contributor
timestamp: November 13, 2017, 09:48:46 am
content: Hello, I was thinking to buy a power meter, because it will be usefull, i don't need of the most expensive piece of equipment, but of good working device. A lab near me is selling a rhode schwarz 115-2 for around 160 euros, I don' t know if is right for me, i usually work on low power application, I know Rhode Schwarz as a very good quality brand, but I dom' t know this deviceAnyone can help me?See you soon

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2017, 10:27:18 am
content: I don't think anyone can help you, when they have no idea what kind of work you do.Did you mean the 8115-2? I don't know of a model 115-2.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 13, 2017, 10:28:10 am
content: Can't find your model number. If it is this one, 160 EUR would be quite a bargain:https://www.rohde-schwarz.com/product/hm8115-productstartpage_63493-44099.htmlEdit: This thing doesn't do much more than a 10 EUR plug adaptor from Reichelt, also called Power Meter, anyway, it's a proper lab instrument and this way still a bargain.

author: NiaDebesis
author_rank: Frequent Contributor
timestamp: November 13, 2017, 10:47:15 am
content: I usually do troubleshooting and project (now I am working to an valve amplifier) The model is a 8115-2 (missclick) if you have better options i will be very happy to know

author: capt bullshot
author_rank: Super Contributor
timestamp: November 13, 2017, 10:59:27 am
content: The HM8115-2 model is intended to be used at power line frequency and is quite limited in frequency response, so it would be a good choice to measure the power consumption of your amplifier, but such a thinghttps://www.reichelt.de/Energiemessgeraete/KD-306/3/index.html?ACTION=3&LA=2&ARTICLE=138036&GROUPID=5664&artnr=KD+306&SEARCH=%252Awill give you the same results.It isn't a good choice to measure an amplifiers output power. You should look for a wider frequency range.

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2017, 11:10:50 am
content: Quote from: capt bullshot on November 13, 2017, 10:28:10 amIts does a lot more than a plug adaptor, although it is pretty basic for a bench power meter. It:works accurately from DC to 1kHzhas isolated voltage and current signal inputs, allowing a lot of flexibility in attaching it to a systemhas real time analogue output, and gives regular digital reportsmeasures reactive power, apparent power and power factoroffers reasonable and well specified accuracy, although its accuracy is actually not that great for a bench power meter (0.8% +- 10 counts)Most plug power meters are pretty awful. A genuine Kill-a-watt does a pretty reasonable job on 50Hz or 60Hz mains measurement. However, most cheap plug power meters give horrible results on anything but a perfect power factor and clean voltage and current sine waves, and even then aren't very accurate. Many just measure RMS voltage and RMS current, and multiply the two. This makes no allowance for waveform distortion or poor power factor at all.If the OP is trying to measure power out of an audio amplifier this is not an appropriate instrument. If the OP is trying to measure AC or DC power consumption it could be a reasonable choice.I don't know how much these cost new, but they shouldn't be very expensive. $2000 or so gets you an instrument from people better known for supply power measurement, like Yokogawa or Chroma, which has a wider bandwidth (to capture more mains harmonics), will break down all the harmonics, and offer 0.1% accuracy.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 13, 2017, 11:24:28 am
content: Quote from: coppice on November 13, 2017, 11:10:50 amWell, that depends ...I've seen the ugly ones, but if you manage to buy one that incorporates a real "energy meter" chip, their results are surprisingly accurate - the one I mentioned is supposed to be such one, but I can't guarantee since models change to fast.

author: NiaDebesis
author_rank: Frequent Contributor
timestamp: November 13, 2017, 11:24:55 am
content: I was hoping for something that cost around 300 bucks, I have checked Chroma and the other brand, but they are far far from my budget

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2017, 11:29:01 am
content: Quote from: NiaDebesis on November 13, 2017, 11:24:55 amAre you trying to measure the power output of your amps, or the power consumption? Chroma, Yokogawa, Kikusui and most other respected makers of things simply called "power meter" only make meters suitable for power supply measurement. If you want to measure audio power you need to look for something specifically described as an audio power meter.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 13, 2017, 11:33:48 am
content: I've bought some time ago one of these:http://www.helmut-singer.de/pdf/clarke2330.pdfFor a price about your budget (don't know the exact number), working and tested, but not calibrated. Since accuracy was rather bad (around 1...2 % error) I had to find out the hard way (no documentation available) how to adjust it. It has enough bandwidth and ranges to measure the power consumption and also the power output of audio amplifiers, but doesn't do anything else.Edit: At least Yokogawa also has wide bandwidth power meters / analyzers, but I haven't seen them yet for less than 1000 EUR on the bay.

author: NiaDebesis
author_rank: Frequent Contributor
timestamp: November 13, 2017, 11:35:42 am
content: Ah..no, missunderstood, probably fault of my english..I need to measure the power consumption, the valve amp was an example of what project I do, an audio power metere will be pretty good, but I need to measure power consumption more often

author: capt bullshot
author_rank: Super Contributor
timestamp: November 13, 2017, 11:38:05 am
content: OK, the HM8115-2 will be a bargain then. You'll get a proper lab instrument, but remember, it isn't Rohde & Schwarz, it's still a former Hameg device (not the quality level of R&S).

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2017, 11:39:53 am
content: Quote from: capt bullshot on November 13, 2017, 11:24:28 amThere is nothing to stop a good AC mains power meter being sold for $10, and a few are. The snag is its a crap shoot, with an awful lot of crap in the market. There are perfectly good energy metering chips for 20 cents or so. Add a cheap MCU, LCD panel, and an RC supply and you have a workable meter. Actually bother to calibrate it during production, and you can have 0.5% accuracy over a wide dynamic range. For less than $1 you can get a fully integrated MCU with energy measurement, and the flexibility to perform a wider range of measurements. The snag is that you can do the crude multiplication of RMS measurements for a couple of cents less, and people regularly do. If you find one of the no-name devices is doing a proper job, when you order some more, they may have gone through a cost reduction.Some of the nastiest plug meters I have seen actually have fairly well known names on them. Those guys like long stable production runs, so they offer predictable nastiness.

author: NiaDebesis
author_rank: Frequent Contributor
timestamp: November 13, 2017, 11:44:20 am
content: Nothing found about the clark hessOnly thishttps://m.ebay.com/itm/Clarke-Hess-255-Power-Analyzer/232537563449?hash=item362451a139:g:J6sAAOSwu~ZZc7op

author: capt bullshot
author_rank: Super Contributor
timestamp: November 13, 2017, 11:58:54 am
content: Quote from: NiaDebesis on November 13, 2017, 11:44:20 amDon't buy this for this price. It's pretty old and crude.QuoteThat exactly matches my experience ...