Yokogawa CW-10 or Wattman HPM-100A - Page 1
Forum section: electronics / testgear

author: djacobow
author_rank: Super Contributor
timestamp: February 28, 2014, 05:15:20 am
content: Has anybody had experience with either of these units? How they perform, accuracy wise, with small loads < 10W?A lot of my work is in energy efficiency and I would like to have a decent instrument for measure the power consumption of AC devices. I have a few Kill-A-Watts and they are fine as far as they go, but they are pretty inaccurate. I have units that differ by more than 5%. Also, they are not very helpful for very small loads like the "vampire" loads of many standby power supplies that have relatively high crest factors.In a prior job I had access to a lab with some beautiful power measurement equipment, including some multi-channel Yokogawa machines that could do thee (or more!) phases, work with or without CTs, etc, all with many digits of precision.I don't have access to that gear today, but would love to have something that Didn't Suck and could still do decent measurements.Is there anything else out there under $500?-- dave jPS -- I haven't tried rolling my own, but I have tried using a two channel oscilloscope with one channel connected to a CT, the other measuring voltage, and using the math function to multiply. Pretty sketchy setup, but kinda works. But scopes have 8b or less resolution, so it's not a great solution.PPS - Anyone have any idea how to get a hold of an HPM-100A in North America? They don't even appear on E-Bay

author: djacobow
author_rank: Super Contributor
timestamp: February 28, 2014, 07:08:01 pm
content: Just bumping here.Really, nobody here has an AC power meter they want to talk about??

author: skipjackrc4
author_rank: Regular Contributor
timestamp: February 28, 2014, 07:17:21 pm
content: I've not found anything, so I built my own. There was a really old Yokogawa on eBay a few months ago for <$200. I doubt it's still up.

author: djacobow
author_rank: Super Contributor
timestamp: February 28, 2014, 07:54:29 pm
content: Skipjack,I'm definitely interested in how your built your own. What kinds of ADCs did you use, how fast, what precision, etc. Also, how did you calibrate it?I made a power meter a couple of years ago using an AVR and its 12b ADCs, a CT for current and a resisitive divider and clamp for the voltage. Put the AVR ground on neutral and powered it with a battery.It worked, but not great.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: February 28, 2014, 08:58:26 pm
content: I used RMS to DC converters, and then just used a 12 bit ADC to read the DC value. This gives about 0.5% accuracy for the RMS conversion (at reasonable crest factors). Instantaneous power was measured by an analog multiplier and averaging circuit. Not the most high tech method, but it is reasonably accurate. Calibration was done by comparing the measurements with DMMs for the voltage and current measurements and by confirming that the multiplier and averager work well with controlled input signals (from a function generator). It's no Yokogawa, but it's good enough for what I use it for. Current sensing was done with a hall effect for the 20A range (I wanted to be able to see DC, so no CT) and a shunt resistor for the 3A and 0.3A ranges.

author: mos6502
author_rank: Frequent Contributor
timestamp: February 28, 2014, 09:58:03 pm
content: How about the Metrahit Energy?Granted, it's a bit above your budget.

author: EEVblog
author_rank: Unknown
timestamp: February 28, 2014, 10:17:56 pm
content: I just got one of these PM300's:http://www.westek.com.au/wp-content/uploads/2012/08/PM100-PM300.pdfHaven't use it yet though.Owned by Tek now, and discontinued.My mate Doug Ford likes the Prova 8500:http://www.triotest.com.au/shop/en/ac-power-sources/2088-prova-8500-electric-energy-saving-tester.html

author: djacobow
author_rank: Super Contributor
timestamp: February 28, 2014, 10:20:29 pm
content: Oh, the Metrahit Energy looks perfect. I'd love to own that, as its a nice DMM in itself. But in the US it seems to be > $1200. Maybe if I hadn't already bought an 87V and 34401A.This is frustrating. I guess because it's such a specialized need, these guys can charge a lot, because fundamentally measuring power is not rocket science.I think I will try to see if I can get the Korean unit on Fleabay. It claims capability of doing low power measurements accurately. The clamp-on YEW is really meant for motors and other high power stuff.

author: djacobow
author_rank: Super Contributor
timestamp: February 28, 2014, 10:21:18 pm
content: Thanks for the extra leads, Dave!

author: mos6502
author_rank: Frequent Contributor
timestamp: February 28, 2014, 10:25:03 pm
content: Quote from: djacobow on February 28, 2014, 10:20:29 pmIt's $912 here:https://www.valuetronics.com/detail/New-gossen-metrawatt-metrahit-energy-m249a.cfm

author: EEVblog
author_rank: Unknown
timestamp: February 28, 2014, 10:25:21 pm
content: I also have one of these kits (older style, you've seen in a few videos):http://www.altronics.com.au/index.asp?area=item&id=K46000.01W resolution

author: EEVblog
author_rank: Unknown
timestamp: February 28, 2014, 10:26:20 pm
content: $808 or best offer:http://www.ebay.com/itm/NEW-PROVA-8500-Energy-Saving-Tester-Meter-TES-/300721823694?pt=LH_DefaultDomain_0&hash=item46046adfce

author: mos6502
author_rank: Frequent Contributor
timestamp: February 28, 2014, 10:36:42 pm
content: Quote from: EEVblog on February 28, 2014, 10:26:20 pmA nice unit I'm sure, if you need the features, but the Metrahit Energy is way more accurate: 0.4%+20 counts vs. 1%+0.5W ... at a 5W load, that would be already a 0.55W or 11% inaccuracy, whereas the Metrahit Energy would be only 40mW or 0.8% inaccurate.

author: Lightages
author_rank: Unknown
timestamp: February 28, 2014, 10:40:08 pm
content: I have the Uni-T UT71E.http://uni-trend.com/UT71E.htmlIt is ok, but I was disappointed with its out of the box accuracy, mine was 0.4% not 0.25%, and the input protection is such that it really should be connected to mains in any way. Other than that it is a full featured meter that can measure power and do computer logging with the included cable and software. This ebay seller seems to have a good deal right now:http://www.ebay.com/itm/UT71E-39999-counts-True-RMS-Digital-Multimeter-Power-Meter-USB-interface-/251244783745?pt=LH_DefaultDomain_0&hash=item3a7f5b2881I can't say that I recommend the UT71E, I am just showing one of the options.

author: Frost
author_rank: Regular Contributor
timestamp: February 28, 2014, 10:48:01 pm
content: Quote from: mos6502 on February 28, 2014, 10:36:42 pmIf accuracy at low loads is important, then the LMG95 from ZES Zimmercould be the right device.http://www.zes.com/english/products/single-phase-precision-power-analyzer-lmg95.html

author: EEVblog
author_rank: Unknown
timestamp: February 28, 2014, 11:17:37 pm
content: Quote from: mos6502 on February 28, 2014, 10:36:42 pmYep, haven't looked at the specs, no idea about the Prova at low loads.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 28, 2014, 11:32:46 pm
content: Quote from: djacobow on February 28, 2014, 10:20:29 pmThe Metrahit Energy is actually cheaper in the US. Just over $900.https://www.valuetronics.com/detail/New-gossen-metrawatt-metrahit-energy-m249a.cfm#.UxEb6mBfr4YThere is a cheaper alternative still, if you are patient, the discontinued Metrahit 29S comes up once in a while on eBay Germany, for about half of that price.

author: Frost
author_rank: Regular Contributor
timestamp: February 28, 2014, 11:43:26 pm
content: Quote from: Wytnucls on February 28, 2014, 11:32:46 pmBetween 250 and 300 EuroGossen charges 133 Euro plus shipping for the DAkkS recalibration.

author: djacobow
author_rank: Super Contributor
timestamp: March 01, 2014, 05:48:33 pm
content: >If accuracy at low loads is important, then the LMG95 from ZES Zimmer> could be the right device.>http://www.zes.com/english/products/single-phase-precision-power-analyzer-lmg95.htmlYes, that is the primary aim, measuring and analyzing standby power.I'm so glad this thread came alive. I have a lot of units to check out now!

author: djacobow
author_rank: Super Contributor
timestamp: March 01, 2014, 05:57:30 pm
content: Ooh, the Prova 8500 also synthesizes the test voltage at whatever voltage and frequency you like, so you can make sure all your DUTs are getting 240.0 exactly, or whatever.That is a feature I had written off because I expected it was crazy expensive. Our old power lab had a machine, I forget what kind that could do that. It was really helpful for characterizing power supplies taking out mains variability.

author: quarks
author_rank: Frequent Contributor
timestamp: March 01, 2014, 06:45:11 pm
content: If I need to measure below 0.2 Watt I use my Gossen MetraHit Energy or an ELV EA8000Picture shows standby power of a 230V/USB adapter

author: djacobow
author_rank: Super Contributor
timestamp: March 02, 2014, 12:07:09 am
content: Wow, the price of the EA8000 is certainly in the range. Too bad it's 200-240V only what with me stuck here with wimpy US mains power.

author: quarks
author_rank: Frequent Contributor
timestamp: March 02, 2014, 10:11:46 am
content: maybe these are also worth to have a look at:Metrix PX110 / 120InfratekChauvin ArnouxHameg HM8115-2andhttp://geoffg.net/energymeter.html

author: Wytnucls
author_rank: Super Contributor
timestamp: March 02, 2014, 10:32:14 am
content: There is also the 50,000 count CEM DT-9974, but I haven't seen a price quoted anywhere for it.http://www.cem-instruments.com/en/pro/pro-865.html

author: EEVblog
author_rank: Unknown
timestamp: March 02, 2014, 11:33:55 am
content: Quote from: quarks on March 02, 2014, 10:11:46 amYes, mine has that new firmware.

author: The Electrician
author_rank: Frequent Contributor
timestamp: March 21, 2014, 01:41:12 am
content: Quote from: djacobow on February 28, 2014, 05:15:20 amA low-cost solution to your problem occurred to me. The Kill-a-watt has an internal shunt consisting of a short piece of manganin wire. I bought another Kill-a-watt at Fry's, removed the shunt and measured it. It's a 2 milliohm shunt. I then replaced that shunt with a .2 ohm, 2 watt 5% wirewound resistor, choosing the most accurate one from a bunch of them. Now the modified Kill-a-watt has 100 times the sensitivity. I was able to measure the no load draw of a modern wall wart at .077 watts. The maximum power measurable is now 18 watts. I compared the reading with my high sensitivity, low power factor Yokogawa wattmeter, and it was very close.For the final accuracy check, I just set the modified Kill-a-watt to measure current with a small load, and compared that to the simultaneous current reading meaured with a DVM. The modified Kill-a-watt reads 2% low. A person could trim the .2 ohm shunt, or just add 2% to the reading. To trim, I would start with a .2 ohm resistor that measured high with full length leads, as measured with a 4 terminal ohmmeter, and then you could solder in the resistor with near full length leads, and then shorten them as a method of trimming. Or, solder in a .22 ohm resistor and solder in an additional resistor in parallel to trim.You probably don't need exceptional accuracy for vampire loads, and this solution is well within your budget.

author: djacobow
author_rank: Super Contributor
timestamp: March 21, 2014, 01:46:46 am
content: I've already got two Kill-A-Watts so this seems like a reasonable hack to try. Thanks!

author: JayF
author_rank: Newbie
timestamp: April 07, 2014, 10:02:03 am
content: There are a few power analyzers out there designed for accurate low-power standby measurements.Yokogawa WT310http://tmi.yokogawa.com/products/digital-power-analyzers/digital-power-analyzers/wt300-series-digital-power-meters/Tektronix PA1000http://uk.tek.com/power-analyzer-series/pa1000as well as ZES LMG95 belowQuote from: djacobow on March 01, 2014, 05:48:33 pm

author: JayF
author_rank: Newbie
timestamp: April 07, 2014, 10:06:34 am
content: There are a few power analyzers out there designed for accurate low-power standby measurements.Yokogawa WT310http://tmi.yokogawa.com/products/digital-power-analyzers/digital-power-analyzers/wt300-series-digital-power-meters/Tektronix PA1000http://uk.tek.com/power-analyzer-series/pa1000]http://uk.tek.com/power-analyzer-series/pa1000as well asZES LMG95belowQuote from: djacobow on March 02, 2014, 04:48:33 AM>If accuracy at low loads is important, then the LMG95 from ZES Zimmer> could be the right device.>http://www.zes.com/english/products/single-phase-precision-power-analyzer-lmg95.htmlYes, that is the primary aim, measuring and analyzing standby power.I'm so glad this thread came alive. I have a lot of units to check out now!

author: pol098
author_rank: Newbie
timestamp: February 07, 2015, 10:09:22 pm
content: Quote from: The Electrician on March 21, 2014, 01:41:12 amFor anybody coming to this oldish thread:This has been discussed in another (older) thread here, with some oscilloscope measurements:https://www.eevblog.com/forum/projects/measuring-standby-power/30/I also made a note of other URLs a while ago, haven't looked recently and don't remember details:http://ecorenovator.org/forum/appliances-gadgets/3597-hacking-kill-watt-very-low-power-measurements.htmlHTH