Author Topic: EEVblog #589 - Voltech PM300 Power Analyser Teardown  (Read 18467 times)

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Offline EEVblog

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« Last Edit: March 12, 2014, 09:08:15 am by EEVblog »
 

Offline Bored@Work

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #1 on: March 12, 2014, 09:29:54 am »
From their web page
Quote
1995 Produced two low cost power analysers, the PM100 and PM300.

So an almost 20 year old, mid 90th design.
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Offline EEVblog

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #2 on: March 12, 2014, 09:35:22 am »
From their web page
Quote
1995 Produced two low cost power analysers, the PM100 and PM300.
So an almost 20 year old, mid 90th design.

Ah, didn't spot that. Sound right. My guess was lat 90's design, likely based on an even earlier design.
 

Offline senso

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #3 on: March 12, 2014, 09:52:54 am »
So how do they got the 250Khz bandwidth from the 50Khz ADC?
Did you measure the current shunt resistance?
 

Offline NiHaoMike

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #4 on: March 12, 2014, 10:51:44 am »
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.
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Offline TheGreatGooglyMoogly

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #5 on: March 12, 2014, 02:12:23 pm »
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)
 

Offline mpep

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #6 on: March 12, 2014, 05:54:57 pm »
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.
 

Offline German_EE

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #7 on: March 12, 2014, 09:02:20 pm »
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.
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Offline mikepa

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #8 on: March 12, 2014, 10:41:01 pm »
Would have liked to see it working albeit with a single phase ... or was the French aspect putting you off using it?
 

Offline Refrigerator

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #9 on: March 13, 2014, 02:19:12 am »
That top board is designed to swing over  :palm:, all you need to do is undo the two screws at the front and leave those at the back . :D
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Offline vanarebane

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #10 on: March 13, 2014, 04:33:20 am »
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
 

Offline c4757p

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #11 on: March 13, 2014, 04:54:51 am »
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

Go in the same room and turn on another large load (vacuum cleaner, toaster...) while watching the lights.
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Offline SeanB

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #12 on: March 13, 2014, 05:18:44 am »
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.
 

Offline jeroent

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #13 on: March 13, 2014, 08:38:35 am »
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.
 

Offline EEVblog

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #14 on: March 13, 2014, 08:44:45 am »
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.

Yes, turns out it does.
 

Offline EEVblog

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #15 on: March 13, 2014, 08:47:04 am »
Would have liked to see it working albeit with a single phase ... or was the French aspect putting you off using it?

It's a teardown video, not a show off it's capabilities video, you can read the manual for that.
 

Online tom66

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #16 on: March 13, 2014, 10:53:30 am »
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.
 

Offline EEVblog

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #17 on: March 13, 2014, 12:39:28 pm »
It's odd, to see such an ancient design still made in 2003

Not when it was released in 1995. An 8 year production life is not uncommon for gear like this.
 

Offline EEVblog

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #18 on: March 13, 2014, 12:42:04 pm »
It looks like Tek discontinued production though.... not sure what technology Voltech would have contributed unless it was some obscure patent.

A 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%?
 

Offline mjkuwp

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #19 on: March 13, 2014, 01:47:56 pm »
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

Diy?  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.

 

Offline Pillager

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #20 on: March 13, 2014, 05:06:43 pm »
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

Go in the same room and turn on another large load (vacuum cleaner, toaster...) while watching the lights.

Meaning 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.).
Greets

Tom
 

Offline hikariuk

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #21 on: March 13, 2014, 09:38:24 pm »
There's a PM100 on eBay UK atm, starting bid of £400.
I write software.  I'd far rather be doing something else.
 

Offline rs20

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #22 on: March 13, 2014, 10:24:44 pm »
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.

Just 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?
 

Offline nitro2k01

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #23 on: March 14, 2014, 12:23:17 am »
Just 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.
The 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, you are sampling 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 the full power signal 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.
« Last Edit: March 14, 2014, 12:25:18 am by nitro2k01 »
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Offline rs20

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Re: EEVblog #589 - Voltech PM300 Power Analyser Teardown
« Reply #24 on: March 14, 2014, 12:41:55 am »
The 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, you are sampling from the same waveform.

Let'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.
 


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