EEVblog #589 - Voltech PM300 Power Analyser Teardown - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: March 11, 2014, 09:56:21 pm
content: Inside the Voltech PM300 3 Phase Power Analyser.The Voltech power analyser division was sold to Tektronix in March 2013:http://www.voltech.com/News/NEWS3.aspxhttp://www.tek.com/voltech-pa-redirecthttp://www.voltech.com/Datasheets:http://www.westek.com.au/wp-content/uploads/2012/08/PM100-PM300.pdfhttp://www.analog.com/static/imported-files/data_sheets/AD7575.pdfhttp://www.avagotech.com/docs/AV02-0940ENhttp://www.ti.com/lit/ds/schs122j/schs122j.pdf!Private video

author: Bored@Work
author_rank: Super Contributor
timestamp: March 11, 2014, 10:29:54 pm
content: From their web pageQuoteSo an almost 20 year old, mid 90th design.

author: EEVblog
author_rank: Unknown
timestamp: March 11, 2014, 10:35:22 pm
content: Quote from: Bored@Work on March 11, 2014, 10:29:54 pmAh, didn't spot that. Sound right. My guess was lat 90's design, likely based on an even earlier design.

author: senso
author_rank: Frequent Contributor
timestamp: March 11, 2014, 10:52:54 pm
content: So how do they got the 250Khz bandwidth from the 50Khz ADC?Did you measure the current shunt resistance?

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 11, 2014, 11:51:44 pm
content: They're probably doing equivalent time sampling, just like a DSO. And likely some downsampling to get way more than 8 bits of resolution from the 8 bit ADCs.The design is a little similar to what I did for the power measurement part of my senior design project, except I used a modern dsPIC, 16 bit ADC for the current channel, and no built in isolation. The isolation was provided with a bunch of high value resistors for the voltage channel and a Hall sensor for the current channel.I wonder if it could be configured as 3 single phase power meters and if it could work down to DC. The latter would make it especially useful for testing efficiency of power supply circuits.

author: TheGreatGooglyMoogly
author_rank: Contributor
timestamp: March 12, 2014, 03:12:23 am
content: Dave,is it just me or in the video it looks like the Avago opto-isolators look mis-spaced and not seated flush? If so, beginners mistake (I have made it a few times with DIP chips)

author: mpep
author_rank: Newbie
timestamp: March 12, 2014, 06:54:57 am
content: Enjoyed the tear down.Next thing, does it work?I actually thought that the sampler circuits might be powered by the phase under test.Does sound like a convoluted way to power them as it is now though.

author: German_EE
author_rank: Super Contributor
timestamp: March 12, 2014, 10:02:20 am
content: The transformer isolation on the power bus is fascinating. Best guess on the need for twin transformers is that a single transformer would need two windings with lots of turns and this would have a risk of flashover.

author: mikepa
author_rank: Contributor
timestamp: March 12, 2014, 11:41:01 am
content: Would have liked to see it working albeit with a single phase ... or was the French aspect putting you off using it?

author: Refrigerator
author_rank: Super Contributor
timestamp: March 12, 2014, 03:19:12 pm
content: That top board is designed to swing over, all you need to do is undo the two screws at the front and leave those at the back .

author: vanarebane
author_rank: Contributor
timestamp: March 12, 2014, 05:33:20 pm
content: So this product helps to test other mains products?I have problem with my DIY reflow oven that, when operable, makes all the lights in the house flicker. I suspect that switching Solid State Relay in PWM mode, that it makes the mains voltage somehow off the standards.. With this tool, I would be able to find the problem of this flicker?Maybe there is a tech university nearby that can give a test with some similar tool to this...Great vid, Dave!Thanks

author: c4757p
author_rank: Super Contributor
timestamp: March 12, 2014, 05:54:51 pm
content: Quote from: vanarebane on March 12, 2014, 05:33:20 pmGo in the same room and turn on another large load (vacuum cleaner, toaster...) while watching the lights.

author: SeanB
author_rank: Super Contributor
timestamp: March 12, 2014, 06:18:44 pm
content: I guess the reason for the odd spare IDC connector is that the single phase unit uses it only, with a smaller display. The 3 phase probably was designed to use a plug compatible display, but this went obsolete and they did the extra shift registers to use pins on the interconnect instead of respinning the board and losing the ability to have a common board, and did a firmware upgrade.

author: jeroent
author_rank: Newbie
timestamp: March 12, 2014, 09:38:35 pm
content: Perhaps the PM100 has a different (less pixels) LCD module as compared to the PM300, and could this explain the pin count difference on the ribbon cable connectors on mainboard and PM300 interface board.

author: EEVblog
author_rank: Unknown
timestamp: March 12, 2014, 09:44:45 pm
content: Quote from: jeroent on March 12, 2014, 09:38:35 pmYes, turns out it does.

author: EEVblog
author_rank: Unknown
timestamp: March 12, 2014, 09:47:04 pm
content: Quote from: mikepa on March 12, 2014, 11:41:01 amIt's a teardown video, not a show off it's capabilities video, you can read the manual for that.

author: tom66
author_rank: Super Contributor
timestamp: March 12, 2014, 11:53:30 pm
content: It's odd, to see such an ancient design still made in 2003, but I guess it's a case of them not selling many a year, so re-engineering it would be too expensive for any savngs they'd make from lower cost components.For example, you could pretty much replace that whole front end with a power meter IC, e.g. ADE7783, which costs £1.50 in volume. Add in a modern MCU (any ARM with an FPU springs to mind, e.g. STM32), a single-rail DC/DC for each channel and you're done.It looks like Tek discontinued production though.... not sure what technology Voltech would have contributed unless it was some obscure patent.

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2014, 01:39:28 am
content: Quote from: tom66 on March 12, 2014, 11:53:30 pmNot when it was released in 1995. An 8 year production life is not uncommon for gear like this.

author: EEVblog
author_rank: Unknown
timestamp: March 13, 2014, 01:42:04 am
content: Quote from: tom66 on March 12, 2014, 11:53:30 pmA couple of complete production ready products, with all the firmware, hardware and circuit design etc done. Do those all-in-one power chips do 0.01%?

author: mjkuwp
author_rank: Unknown
timestamp: March 13, 2014, 02:47:56 am
content: Quote from: vanarebane on March 12, 2014, 05:33:20 pmDiy? You may be able to run really slow pwm. On mine I only run at 1hz. And probably could go slower. I use zero-crossing SSRs which also may help.

author: Pillager
author_rank: Unknown
timestamp: March 13, 2014, 06:06:43 am
content: Quote from: c4757p on March 12, 2014, 05:54:51 pmMeaning that your oven probably draws a considerable amount of current on startup (switching on), just like a vacuum cleaner or power tools without soft start feature.Drawing a high current means a higher voltage drop in the wiring in your house (Ohm's law), so you will effectively have a lower voltage on other power points (lights, etc.).

author: hikariuk
author_rank: Unknown
timestamp: March 13, 2014, 10:38:24 am
content: There's a PM100 on eBay UK atm, starting bid of £400.

author: rs20
author_rank: Super Contributor
timestamp: March 13, 2014, 11:24:44 am
content: Quote from: NiHaoMike on March 11, 2014, 11:51:44 pmJust to define the term for everyone, Equivalent Time Sampling is when you take advantage of the fact that a waveform repeats, so by sampling 10 different cycles of the same waveform at 50kHz with slightly different offsets on the ADC timing, you can recover a signal sampled at 500kHz. This only works if every cycle of the signal is identical, though.And this got me thinking, the high frequency noise injected by a switch mode supply is very unlikely to be phase-locked to the mains frequency, so this assumption seems completely invalid, doesn't it? The phase of the switch noise with respect to mains phase will be different each cycle. On the flipside, any harmonics will be just fine (judging from the PM100 manual, harmonics are very fundamental [no pun intended] to what this meter does), and if you just wanted to measure the RMS non-harmonic noise, I guess you could just take the RMS of all the recorded values (minus the 50Hz fundamental) -- perhaps you don't really need the points to form a meaningful curve.Does seem a bit dodgy nevertheless though, right?

author: nitro2k01
author_rank: Frequent Contributor
timestamp: March 13, 2014, 01:23:17 pm
content: Quote from: rs20 on March 13, 2014, 11:24:44 amThe way I understand EST, and correct me if I'm wrong, is that you have lower-rate ADCs sampling at a 360/n degree offsets. So you might have a 100 kHz clock driving two 50 kHz ADCs at offsets, giving every second clock pulse to each respective ADC. In other words, youaresampling from the same waveform.But unless they've overclocked the ADCs (or come up with a way to disprove the Nyquist-Shannon theorem :p ) that won't get them anywhere near the claimed 250 kHz bandwidth. Actually, looking closer at the datasheet, what is claimed is that thefull powersignal bandwidth of the ADC is 50 kHz, which I guess means there's a roll-off above that frequency? The conversion time of the ADC is 5 µs, giving an effective sample rate of 200 kHz if run at the maximum speed, or for two running in parallel, 400 kHz, giving a crusty 200 kHz effective Nyquist bandwidth. Not quite 250 kHz, but we're starting to get into the plausible territory.

author: rs20
author_rank: Super Contributor
timestamp: March 13, 2014, 01:41:55 pm
content: Quote from: nitro2k01 on March 13, 2014, 01:23:17 pmLet's not get too bogged down in nomenclature, but the "equivalent" in Equivalent Time Sampling is talking about finding equivalent times in different cycles. I googled "Equivalent Time Sampling", and the first two results are notes from Tektronix and Agilent explaining how Equivalent Time Sampling can't do single-shot (at the ETS sampling rate) for this very reason.Yes, many oscilloscopes use multiple physical ADCs clocked at different phases to effectively produce a single ADC operating at a higher sampling rate. This is different from Equivalent Time Sampling, and it can't be what's happening inside the PM300 because the PM300 only has one physical ADC for each of its 6 channels (6 channels being v1, i1, v2, i2, v3, i3). Assuming each chip is single channel.

author: JackOfVA
author_rank: Unknown
timestamp: March 13, 2014, 01:55:25 pm
content: The A/D data sheet says the sample rate that can be realized is slew rate limited, up to the 200 KS/s maximum based on the recommended clock speed and number of clock cycles for conversion.Opportunity for some games here by reducing the voltage applied to the A/D's input S/H stage (thereby reducing the slew rate) and also reducing the A/D voltage reference to maintain the dynamic range?

author: vanarebane
author_rank: Contributor
timestamp: March 13, 2014, 02:52:01 pm
content: Quote from: c4757p on March 12, 2014, 05:54:51 pmThe lights only got a bit less darker. What does this tell you?

author: delmadord
author_rank: Regular Contributor
timestamp: March 13, 2014, 02:53:19 pm
content: Dave,I would also like to see that puppy in action. At this point, I can only imagine it is doing the dishes :-D Will there be quick review please?

author: c4757p
author_rank: Super Contributor
timestamp: March 13, 2014, 02:56:07 pm
content: Quote from: vanarebane on March 13, 2014, 02:52:01 pmI was hoping it would tellyousomething. The lights willalwaysdim when loads are switched, you're not going to get around that. It has more to do with your wiring than with the device connected to it.Try slowing down your PWM a bit to see if it makes it less annoying. Or speed it up so you can't see the flicker, but then power dissipation in the switch will increase.

author: vanarebane
author_rank: Contributor
timestamp: March 13, 2014, 03:08:11 pm
content: Quote from: c4757p on March 13, 2014, 02:56:07 pmYes I was already editing my first post when you already answered.I followed the DIY reflow oven instructions here:It uses PWM to turn on and off the power to the heater and has no soft-start or such, so yes, this makes the power jump up and down causing the flicker effect. This was my initial though also.Changing the PWM would change the heating properties yes, but the oven is doing the reflow nice now and I'm afraid that changing PWM would make it not work on the reflow part. The flickering is not that annoying, I can turn some lights off or leave the room while reflowing, but I'm afraid of damaging other nearby more sensitive mains devices. Two laptop chargers already have started to act weird (laptops run in the lowest CPU speed when plugged and full power when on battery, 2 chargers, 2 laptops with same responses)Would it help if the mains voltage is stored in some sort of cap or inductor?I guess I could start a new thread on that instead of sidetracking it here.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: March 13, 2014, 03:40:12 pm
content: Quote from: c4757p on March 13, 2014, 02:56:07 pmI would fully expect that in a 120V country (*recalls Dave's story about the copying machine he tried to use in the US and sniggers and giggles*) but not so much in a 230V country. I live in Sweden, a 230V country where the wiring is typically properly installed, and I never really notice any flicker when turning on heavy appliances like a vacuum cleaner, microwave oven or a toaster, even when the lamp is connected to the same phase as the appliance.I would guess vanarebane's mains wiring is simply underdimensioned. As a short term solution, I would recommend getting an extension cable that you connect to the power outlet with the shortest path to the fusebox, and route that to the room with the oven and use that for the oven. Make sure the extension cable is rated for the current the oven is using, of course. As a long-term solution, I would get the mains wiring checked out by an electrician and maybe replaced, if I were you.

author: hikariuk
author_rank: Unknown
timestamp: March 13, 2014, 04:08:38 pm
content: Quote from: nitro2k01 on March 13, 2014, 03:40:12 pmAssuming his flag is accurate, vanarebane is in Estonia, which is also 230V.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: March 13, 2014, 06:04:22 pm
content: Quote from: hikariuk on March 13, 2014, 04:08:38 pmIndeed. The first paragraph is for c4757p and the second one is for vanarebane .

author: kriebz
author_rank: Newbie
timestamp: March 13, 2014, 09:20:30 pm
content: Quote from: Dawgie on March 12, 2014, 10:10:01 amOoh, I've actually seen setups like this only much larger, for total isolation. I'm not so good at theory, but as I understand, the low-turns inner segment is at a lower voltage, which means higher current. The inductance of the windings resists current change, i.e. in the case of transients, giving a much cleaner output, at the cost of a fair bit of loss. There might also be a fusible link in the inner circuit. I'll see what else I can find out about this type of circuit.

author: tom66
author_rank: Super Contributor
timestamp: March 13, 2014, 11:10:00 pm
content: Quote from: EEVblog on March 13, 2014, 01:42:04 amYes. We use similar ADE-chips at work and they go through an extensive calibration rig which can get accuracy down to about 0.1%. I'm sure if we tried harder and used a more accurate cal rig, we could do better.

author: vanarebane
author_rank: Contributor
timestamp: March 14, 2014, 04:55:41 am
content: Quote from: hikariuk on March 13, 2014, 04:08:38 pmQuote from: nitro2k01 on March 13, 2014, 03:40:12 pmYup, both right, 230V mains here and you can probably see from that far that house wiring is a bad crows nestAll thanks to my dad, who built this house and did the wiring himself. The oven is quite far from the fusebox and has many shitty crowsnest in between.I went to the fusebox today and the oven performed without flickering other lights. So your hunch was right.Is there any component that I can work into the oven to compensate the flicker?Thanks!

author: calexanian
author_rank: Super Contributor
timestamp: March 14, 2014, 05:34:38 am
content: Not that it would matter but the devices across the current shunt, D13 and D14 kinda smell of TVS's Just a gut feeling looking at the partial part numbers and either an impending stroke or my spidey sense.

author: Pillager
author_rank: Unknown
timestamp: March 14, 2014, 08:29:53 am
content: Quote from: vanarebane on March 14, 2014, 04:55:41 amThis really could have made it's own threadYou can install a soft-start-circuit, but that will likely throw off your oven's performance a bit. You would have to test it and compensate for the changes.Using a separate extension cord from the fuse box is another way, but it shouldn't be permanent. You could put in a new power line from the fuse box to your oven, or let an electrician do it. Do it yourself ONLY IF YOU KNOW WHAT YOU'RE DOING! Mains power is not to be underestimated! Make shure the power is OFF, and you should have another person there, just in case something does happen.

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 15, 2014, 08:55:25 am
content: That's a damn nice instrument.I've got a PM100 (single phase) and it basically tells you everything you'll ever need to know.I also scored a 100:1 current clamp and a 1000:1 shunt all for $50!Hang onto it Dave. I certainly would.Dick

author: EEVblog
author_rank: Unknown
timestamp: March 15, 2014, 11:15:38 am
content: Quote from: Richard Head on March 15, 2014, 08:55:25 amI plan to. I need a good meter like that for the lab. Not easy to come by, or come by cheaply.

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 16, 2014, 02:13:23 pm
content: Meant to say 1000:1 CT.

author: rsjsouza
author_rank: Super Contributor
timestamp: March 17, 2014, 03:26:18 pm
content: That was a very good teardown; growing in the eighties I have a weak spot for discrete logic, despite knowing that one or a few CPLDs/FPGAs could replace the entire set.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 17, 2014, 03:30:57 pm
content: Quote from: vanarebane on March 14, 2014, 04:55:41 amSwap the lamp ballasts for a good quality inverter type with active PFC. (PFC doesn't really do good for home use, but active PFC is also a voltage regulator.)

author: Pilot3514
author_rank: Contributor
timestamp: March 20, 2014, 03:38:45 pm
content: I was wondering why the design uses a shunt instead of a current transformer.My only guess is that the power meter could be used to measure DC power as well.I am interested in building a device to measure and log the voltage, current, and frequency of a two phase generator. I may also want to raise an alarm if the values go outside of set parameters.Any advice to "young players"?

author: SeanB
author_rank: Super Contributor
timestamp: March 21, 2014, 09:02:30 am
content: Shunt likely is cheaper to get trimmed to good accuracy over a wide frequency range than a CT. Ct will have difficulty getting that wide range from 50Hz to 50kHz with sub 1% error without complex compensation or frequency dependant calibration.

author: turbo!
author_rank: Regular Contributor
timestamp: May 06, 2014, 12:19:48 pm
content: This looks like a reasonable low cost design. This one is the same concept as the plug-in type cheap but very accurate kWh meter. They're cheaply built to be within ballpark figure range and calibration is pushed into the Flash ROM. This relies on calibration constants set-in and the difference is in how good the calibration constant stays constant over time and temperature change.The ranging circuits are like your every day DMMs. I think the most expensive component of this instrument is the R&D expense for the program software algorithm in that thing labeled U40. I'm pretty sure Tek bought them, because they wanted the intellectual property behind the software algorithm.The two channels are integrated mathematically in the CPU and accumulated digitally. Big problem with this type of integration is that pulses that slips out of sampling or display refresh will slap past you.

author: turbo!
author_rank: Regular Contributor
timestamp: May 06, 2014, 01:16:19 pm
content: Quote from: Richard Head on March 15, 2014, 08:55:25 amWhat's the software version in yours? Does yours let you change ranges manually or use long integration? I could use new firmware.bin.

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 06, 2014, 02:14:30 pm
content: TurboI haven't used it in a little while so I can't answer you now.I'll power it up later and check the software version.I also have some PM300 units available to me at work. They are housed in the same enclosure as the PM100 but are 3-phase units. I think it's the one Dave did the teardown on.Dick

author: PTR_1275
author_rank: Frequent Contributor
timestamp: November 06, 2015, 11:44:39 am
content: I know I am digging up an old thread, but how easy are the service manuals to find for the Voltech gear? I am trying to find a copy for one now, but keep going around in circles.-Chris

author: bittumbler
author_rank: Contributor
timestamp: September 22, 2016, 01:34:11 pm
content: Hi,sorry for replying to such an old thread, but i just now watched the video.Regarding the "dual ring core transformer" setup, i think this is a form of (electrostatic) shielding.A normal isolating transformer has a capacitance between primary and secondary windings of a few nF.This dual transformer setup reduces the capacitance to a few pF.Both "middle" windings are designed for low voltage/high current (low number of turns) to minimize electrostatic transfer between windings (low voltage means low electrostatic fields).However typically one of the middle windings should have a center tap to ground. That seems to be missing.Another approach to solve the same shielding problem is using coax cables as transformer windings. Then you need only one ring core.The center of the coax will be your normal conducting winding wire. The shield of the coax will be your electrostatic shield to minimize capacitance between primary and secondary.For this device such a shielding seems to be important, because it has multiple separate low impedance ground connections:the power supply that powers it, and the measurement circuits. You want them isolated as much as possible.Best RegardsMatthias