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Forum Index : Microcontroller and PC projects : Mains frequency monitoring

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CaptainBoing

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Joined: 07/09/2016
Location: United Kingdom
Posts: 2170
Posted: 11:03am 14 Oct 2017
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That link above is new. I think NG are revamping their web and the link I used to have had a big 404 where the graph used to be.

British Telecom (BT) have reasonable presences in the US and mainland Europe, British Petroleum (BP) wrecked the gulf of Mississippi - as you rightly pointed out, they go where the money is. It's probably necessary in order to keep going today.

I can't keep track of the directions it moves in or who owns who.

Edited by CaptainBoing 2017-10-15
 
CaptainBoing

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Joined: 07/09/2016
Location: United Kingdom
Posts: 2170
Posted: 11:13am 14 Oct 2017
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  HankR said  

I would like to be more accurate (I believe by law the mains frequency may not be beyond 1% of spec).



In the UK I think you are right although without researching it I don't know what it is.

The Post Offices used to have mains powered clocks that simply plugged in a small mains outlet (so you couldn't plug the vacuum cleaner in it) and they both powered the clock and gave the time sync - with a high degree of accuracy. At that time the PO was part of the government so I am guessing the mains frequency was legislated to be pretty much spot-on.

Years ago, I had software clocks in Z80 systems that used the low-side of the mains transformer in the PSU right before the bridge rectifier, through an opto-coupler to provide a 50Hz interrupt and they never really needed tweaking - set them at power-up and that was it.

There are variances but if it drifts low, I notice there is a tenancy to drift high later so I think the average over a given period is fairly precisely 50Hz (uk)Edited by CaptainBoing 2017-10-15
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 12:07pm 14 Oct 2017
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I just hooked up my old HP5315A counter to a small transformer and measured 50.003974Hz

Dead easy and these counters are not that expensive.
There is one on e-bay right now.
https://www.ebay.com.au/itm/hp-5315a-opt-003-004-Counter-Frequency-Multimetro-Oscilloscopio-Frequenzimetro-/302485933532 ?hash=item466d910ddc:g:ZAcAAOSwM49Z38YB
Cheers,  Tony.
 
Herry

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Joined: 31/05/2014
Location: Australia
Posts: 261
Posted: 01:56pm 14 Oct 2017
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Cap Boing: You can't legislate for spot on because it depends on the load/supply balance which will always vary. British Post Office and Australian one (I think, at least it is depicted in the instructional books)had long case master clocks with compensated pendulum. Warp: far too expensive for me, I'm afraid. Blew my last birthday money on a DSO. But that has severe jitter (a Hertz at a time) so no go. Thanks again all. Some of this is above my head, but is appreciated all. I would like to get an analogue display rather than a graph or table.
Senior?!  Whatever it says, I'm a complete and utter beginner...
 
Herry

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Joined: 31/05/2014
Location: Australia
Posts: 261
Posted: 02:01pm 14 Oct 2017
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[URL=http://www.dynamicdemand.co.uk/grid.htm]

Had another look, and yes it does appear genuine. That is the sort of display I would likeEdited by Herry 2017-10-16
Senior?!  Whatever it says, I'm a complete and utter beginner...
 
HankR
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Joined: 02/01/2015
Location: United States
Posts: 209
Posted: 03:27pm 14 Oct 2017
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  Herry said   Blew my last birthday money on a DSO.


Which one pray tell did you get? And how do you like it aside from the jitter?

I went wild and just bought my first DSO. I've come to my senses now but it's too late to reverse this extravagant purchase.

It's brand new but still (usually buy used test equip.)
It was on sale but still.

Lesson learned is: think about what you're doing before pushing that buy button

Oh, did I mention how far it set me back?

Sad, but it was ................. $14!

Shipping included. Edited by HankR 2017-10-16
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 03:51pm 14 Oct 2017
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My very first DSO was also a thirty dollar e-bay job. The screen is kind of small, but its now installed permanently monitoring my inverter output waveform.

My next DSO was a mid 1980's Tektronix, very likely the very first commercial DSO on the market. Probably the first and last DSO made with a green cathode ray tube.

Its awful to use because at that time nobody really knew how to make a workable user interface for a DSO. So it has a million well hidden features, each of which you have to scroll through several menus deep to access.
The software wonks would love that, but I am a Neanderthal hardware knob twister and its like something out of an alien spacecraft to learn how to use.

The one good thing about it is its still repairable, with nice large through hole components, and the full service manual and schematics are available free online.
All the later DSOs are surface mount, with LCD displays, fewer features and with no schematics available or service manuals, and are essentially unrepairable when out of warranty.

Much prefer my Tektronix analog scope (with real knobs). But digital storage is still very good for very slow events, or capturing a one off event before the trigger point.
I very rarely use this DSO, but its still a very handy thing to have on rare occasions.
Edited by Warpspeed 2017-10-16
Cheers,  Tony.
 
HankR
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Joined: 02/01/2015
Location: United States
Posts: 209
Posted: 06:31pm 14 Oct 2017
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  CaptainB said  
  HankR said  
I would like to be more accurate (I believe by law the mains frequency may not be beyond 1% of spec).

That was me, but only quoting Herry.

  CaptainB said  In the UK I think you are right although without researching it I don't know what it is.

If you look at the almost real time UK grid load meter, you'll see the legal limit departure from 50 Hz marked for what looks like 1% over and 1% under.



 
Herry

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Joined: 31/05/2014
Location: Australia
Posts: 261
Posted: 08:02pm 14 Oct 2017
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DSO is a Hantek DSO 5102P. Haven't done much with it yet. It cost over A$500. Re the meter above. The scale is not linear so difficult to estimate the 'legal' points... But yes, it does appear to be real real time after all!
Senior?!  Whatever it says, I'm a complete and utter beginner...
 
isochronic
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Joined: 21/01/2012
Location: Australia
Posts: 689
Posted: 08:47pm 14 Oct 2017
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I saw an old photo once - a mains frequency meter - it had a number of
resonant steel strips, with a range of 49.5 - 50.5 Hz. A small electromagnet
tickled the lot, the appropriate strip then flickered up and down and the other strips were visibly still. Ah yes..the smell of cooking Bakelite..
 
Herry

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Joined: 31/05/2014
Location: Australia
Posts: 261
Posted: 08:50pm 14 Oct 2017
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Yes, the resonant reed based frequency meter was common in eg telephone exchanges.
Senior?!  Whatever it says, I'm a complete and utter beginner...
 
HardingJohn

Regular Member

Joined: 28/07/2017
Location: Australia
Posts: 78
Posted: 08:13pm 15 Oct 2017
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I use the Atmel ATM90E36A chip with the PIC32MX470 or PIC32MZ2048 chips to read 80 different AC values for an energy management and control solution. The chip is fairly easy to setup and talk to via SPI. It provides rms voltage and current measurement across three phases and even neutral current measurement if you wish and provides a heap of registers for instantaneous active and reactive power and energy accumulation as well frequency and harmonic distortion measurements. You can get under 1 second updated values for frequency with an accuracy of +-0.01 Hz.

Don't play around with live AC unless you really know what you are doing however. Full galavanic isolation is needed between this chip and the Micromite for SPI isolation and separate isolated power supplies.

A safer method is buy a cheap power meter with 2 wire RS485 Modbus RTU. It is very easy to read the Modbus registers using a Micromite COM port, COM enable pin and a RS485 driver chip. Grid frequency is nearly always readable from the Modbus Map for most cheap power meters. You can use a through current meter or a CT based meter and measure grid frequency without connecting anything to the load side of the meter or using any CTs. Just use an inline 100mA fuse on the active voltage sense wire for each phase.

John
Just know enough to get me in trouble, but not quite enough to get me out.
 
HankR
Senior Member

Joined: 02/01/2015
Location: United States
Posts: 209
Posted: 03:32pm 18 Oct 2017
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  Warpspeed said   My next DSO was a mid 1980's Tektronix, very likely the very first commercial DSO on the market. Probably the first and last DSO made with a green cathode ray tube.

All the later DSOs are surface mount, with LCD displays, fewer features and with no schematics available or service manuals, and are essentially unrepairable when out of warranty.

Much prefer my Tektronix analog scope (with real knobs).

Tony,

Could you mention what 3 models for the three scope descriptions you've mentioned?

1. 1980s Tektronix DSO
2. latest of your modern SMD DSO scopes
3. analog Tektronix scope

I vastly prefer knobs to menu systems and their soft buttons. That goes
for ham gear as well.

Hank
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 04:04pm 18 Oct 2017
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Tek 2430 Digital oscilloscope. The service manual was printed in 1986.
It was the very first digital storage oscilloscope Tektronix ever made after a lot of very expensive R&D developing it.

Tek analog oscilloscope 24xx this came in several different versions with various bandwidths and options.
Service manual printed in 1985. It was the very last analog oscilloscope Tektronix made, and arguably the best ever.
It has a lot of comprehensive digital on screen readouts and features, self test, self calibration, adjustable on screen calipers, and so on, but the whole vertical amplifier chain is still all analog right the way through to the CRT. What you see is what is really there !
There are four vertical channels.

The one I have is the 2445B which has four channels and is quoted at a very conservative 200Mhz bandwidth. Versions up to 400Mhz are available. All the features are pretty much the same throughout, the more expensive versions just have greater bandwidth.

All these oscilloscopes were quite large and heavy by todays standards, used the same excellent 400 Mhz green phosphor 14Kv CRT with internal graticule. All used full sized through hole components and the full service manuals are available on the internet.

All of these 24xx series oscilloscopes, both the digital and the analog versions continued in production together for many years more. At the end of that period Tek switched entirely over to digital, but in a much cheaper model with colour LCD, a very short plastic case, a much lower price, and more user friendly.
In many ways it was a backward step.
But Tek were being done to death from the cheap Asian and European competition, so they needed to develop much cheaper models to compete.

Edited by Warpspeed 2017-10-20
Cheers,  Tony.
 
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