Is Aussie mains frequency accurate for clocks?

Hi there,

I am building a nixie tube alarm clock (using 6 in-14's). I had originally picked out a DS1302 RTC to use with a (errr) atmega328 (And found a code library to work with it).

After doing more research I found that North America and Europe compensate/average the mains frequency so that it is long term accurate for time keeping yet I am struggling to find any reference to if this happens in Australia. Does anybody know if we do? My google-fu is failing

Thanks

 

http://electronics.stackexchange.co...s-the-frequency-of-the-ac-electricity-network

I've heard clock radios etc use ac as the clock signal, link suggests not. Clock modules are pretty cheap aren't they? I want to use GPS to time a clock, no timebzone problems then. Isn't there a radio frequency you can tune in to too?

yep, http://en.wikipedia.org/wiki/Radio_clock

 

Pretty Accurate over an extended period.., last time I was in a power station ~10 years ago now, there were 2 clocks on the wall, a stand alone clock, and a 50hz clock linked to the grid, part of the operators job is to adjust the rate of the turbines to keep them in sync...

 

I believe synchronous motors were used a long time ago for clocks to keep the speed.. Problem with radio clock would be that it adds cost to my build, which considering I already have a uC, all I would need to count mains frequency would be an optocoupler, diode and a resistor (which I am guessing would be cheaper than a radio module)

This seems positive

Thanks

 

The compensation is conducted here too, though there are circumstances where an area may go out of overall sync.

Also you have to ignore the controlled load activation/deactivation signals too.

 

an RTC is like 5 bucks http://dx.com/s/RTC.html?sort=Price it's your clock but if I was making one i'd want it to be unnecessarily accurate.

you got a build thread? I want to make a nixie clock one day but i know bugger all about HV and everything else about nixies too.

 

It would suck having to reset it every time there's a blackout.

 

Hmm I am slightly allured by the simplicity of using the mains frequency, I might have to run an experiment and see how accurate it is... It will take a few weeks for the pcb to be made/show up anyway The other aspect is a RTC clock would constantly drift off in one direction, yet the mains frequency may be inaccurate (by at a guess up to a minute for a day or two) but should average out even over long periods, which is what others in this thread are confirming for me

As for the supply, there are two methods: Using a switching/boost convertor, or a transformer (or 2). I will find the link, but some nice old mate has designs on the web for a max1771 based boost convertor for nixies, but I chose the simpler (guaranteed to work the first prototype option) of using two transformers:
240>12v -> 12v>240v -> bridge rectifer + Cap in parallel (and a 1M bleeding resistor). So in other words the secondaries are connected together to give isolated 240v ac. I built this into a wooden box, along with a fuse and a switch: http://www.jaycar.com.au/productView.asp?ID=PP4003

http://www.jaycar.com.au/productView.asp?ID=MM2006

I then have a current limiting resistor going to the anode of the nixie tube.

A 74141 equivalent (A decoder for nixie tubes) is then used to ground the cathode corresponding to the digit that wants to be displayed. These are easily found on fleabay, had 6 delivered for $10 bucks or so.

I'm controlling the 74141 with d-flip flops, but shift registers are probably a better option.

I will post some pictures and schematics.

For the nixie I chose IN-14's for being relatively cheap yet still a decent size (They are considered 'medium' sized). They are best found on eBay, although make sure you grab "New, old stock". The seller included a free 7th tube (albeit well used) which I have rigged up (see picture) for testing purposes. I think mine ended up being about $60 for six, including postage. I can refer you to the seller if you wish.

Overall I'm going to use a wooden enclosure to hide the power supply, and have all the digit logic on a PCB mounted on top of this box. Still figuring out how I'm going to attach the nixie's - Some type of socket would be awesome, I want to try and avoid soldering the tubes themselves if I can.

Click to view full size!
I will do some better picture tommorow

 

Nothing local.

The DS1302 has provision for a backup battery.

2.

 

Lots of micros have watch crystal clock inputs, that is just 1 component to add there.

Get one of these
http://www.ebay.com.au/itm/2-PCS-FE...d-Oscillator-Programmable-10MHZ-/221200987009

I own a non working one of these, HP5061A Cesium Beam Frequency Standard - http://www.flickr.com/photos/eevblog/sets/72157632737905949/

 

If it helps my wall timer?.. Having a mind blank, unit that you plug into the wall, then plug in light, and you can set what times and what days it turns on/off. It has lost two and a bit hours over the space of 1.5 years. Now turns on/off at 4:45am/pm instead of 7 o'clock. I'm assuming it uses the mains frequency to keep time, but I may very well be wrong and might not even apply to your area anyway.

 

Rod seems to think so. http://sound.westhost.com/clocks/motors.html

I remember one of his articles suggesting a test of a mains frequency synced clock against some known standard over, say, a week. Can anyone in Aus help the OP with this?

 

I run a GPS based clock that is sitting under 10nS RMS error.
I'd just need a synchronous clock to compare it with.

2.

 

Most definitely. Any grid operator, will always be playing a game of upping and lowering the frequency based on demand, unplanned events (ie Power Plant going offline) and minimising Accumulated Time Error. In Australia, it looks like this responsibility falls to AEMO (Australian Energy Market Operator). There are standards for what do to when and how etc but AEMO has the final say.

So if something very bad happens they might decide "screw it, time error is zero as of now". But this would be a very extreme event (and most likely your clock would be inaccurate because it lost power).

Back to your original question, there are a few differences in standards for the mainland and Tasmania (cause power to/from Tasmania goes through an undersea cable which complicates things).

To quote the standard on frequency:

For time error:

Note: FCAS = Frequency Control Ancillary service. Basically all the tools at the grid operators disposal for frequency control. (ie power plants in stand-by, cutting power to certain services like hot water etc.)

Bottom line: If you are on the mainland, your clock is within 3.5 seconds. If it's lagging now, it will at some point, speed up to compensate.

Sources:
[1] http://www.aemo.com.au/Electricity/...cy/Frequency_Report_Reference_Guide_v2_0.ashx
[2] http://www.aemo.com.au/Electricity/.../SystemOperatingProcedures/SO_OP_3715v54.ashx

If you are interested there are monthly reports on "Frequency and Time Deviation Monitoring":
http://www.aemo.com.au/Electricity/...Documents/Frequency-and-Time-Error-Monitoring

Edit: grammar

 

Nice work Blue_Yoda.

The GPS clock sounds awesome 2xCPU, that is some serious accuracy.

 

Most power stations in Australia are connected to a grid and the grid is kept in long term sync with an atomic clock. So short term accuracy is not good but long term is as good as it gets. In reality it's more than good enough for domestic clocks.

If you want better short term and long term accuracy it gets tricky. There's the option of receiving WWVH but that too has a problem with changes in the propagation path length causing cyclic errors over a 24 hour period as the height of the ionosphere changes. You can run your own precision clock and compensate that over the long term based on the offset between it and WWVH. The other advantage of the WWV broadcasts is they carry encoded UTC time data which the mains frequency doesn't give you. The other complication is you need a pretty decent aerial to get WWVH here and the receivers to decode the data are complex.

Then there's GPS receivers but the only good ones I've seen were 1RU units.

For any domestic clock the 50Hz mains frequency is more than adequate and the power failure issue is easily dealt with.

 

Thank you very much! Much appreciated! Thanks for taking the time to do that!

So I have rigged up an arduino to run as a test, and it is holding time. (using my phone as a reference.)

 

WEOW!
very informative post! Thank you!

 

The Trimble Thunderbolt is a lot smaller than 1U (in width at least)

Yeah, it's not bad. When I get around to moving the antenna to give it a better view of the sky, it should improve too.

I've never seen a Thunderbolt E offered second-hand, but the old model is available surplus.

2.

 

Interesting discussion...
The Tempo on my wifes Yamaha keyboard has always seemed a little out from my pc recording software. I've always wondered if it was a dodgy 60 -> 50hz conversion.

120bpm on both always fell out of sync in the space of a song....