Power Grid Change May Disrupt Clocks in USA

Ken Nadvornick · Jun 24, 2011

AP EXCLUSIVE: Power grid change may disrupt clocks
By Seth Borenstein, Associated Press Science Writer, via Yahoo! News, June 24, 2011

Uh oh...

There goes all of those Gralab 300 synchronous timers. Mine was manufactured during the Eisenhower administration. It's still so accurate I use it to periodically adjust the real time setting on my solid state Zone VI Compensating Development Timer.

Ken

ic-racer · Jun 24, 2011

20 minutes over a year predicted change. This is unlikely to affect any darkroom equipment to any noticeable degree. Even my Wejex sensitometer with a stepper motor would only be off by 0.002283105 seconds.

DWThomas · Jun 24, 2011

Probably half the clocks here run on battery power. Not sure if my enlarger timer runs off line frequency or not, but having worked in a power station years ago, I can assure you that while there may be drifts over a long period, there won't be sudden changes. Connecting an alternator onto the grid that hasn't been perfectly synchronized in frequency and phase results in loud rumbling, shaking buildings and a circuit breaker the size of a house tripping out!

It's interesting to contemplate -- not too far from here is the Ephrata Cloister, home of a very strict religious sect in the 18th century. They had clocks -- but only with an hour hand -- minute precision was considered unnecessary.

removed account4 · Jun 24, 2011

i use the sun, not the clock

BetterSense · Jun 24, 2011

I have one of those older shelf clocks with the mechanical flippy numbers that I got at a garage sale. Ever since I put it in the garage I've been impressed with how accurate it's been and how easy to read the mechanical numbers are. I would like to get another one for the darkroom. I'm pretty sure those things use the mains as a time source.

PeteZ8 · Jun 24, 2011

I somehow doubt that digital clocks that run off of regulated DC power supplies are going to be affected by a slight change in the grid frequency, or even a huge change in grid frequency.

The only clocks that would be affected are old, 100% analog AC wall clocks, and I honestly cannot remember the last time I saw one in use. Your VCR, DVD player, coffee maker, stove, alarm clock, electric toothbrush and anything else with a digital clock on it should not be affected.

Leigh B · Jun 25, 2011

The 20 minutes/year error is only 0.004%, hardly significant for enlarger timers or similar applications.

Anybody who needs precision time now uses GPS, with errors on the order of 0.000000000001%.

- Leigh

Chirs Gregory · Jun 25, 2011

Crystal clocks (quartz and the like) use an oscillator where the frequency is determined by the size and shape of the crystal itself, not voltage or current. Likewise, the venerable 555 timer IC's oscillation frequency is based on the ratios of resistors and capacitors, and as long as the voltage supply is enough to get the thing working the frequency should stay constant. Another way of doing timing stuff would be a microcontroller of some sort, but those generally also have set clock frequencies that are pretty much entirely independent of current and voltage. And all of those components rely on DC, which unlike AC really shouldn't have a base frequency at all, as it's just a constant stream of electrons from negative to positive. (At least that's my understanding of how it all works; I've been getting my soldering iron wet with some photo-related circuit design lately and I've begun to both love and hate the 555 with equal passion.)

The thing I'd be worried about is a slight change in voltage screwing with the brightness of the enlarger bulb. Before I got a timer (and a brain I guess) my Omega was plugged into a power strip along with a little radiant heater thing, and any time the thermostat would switch the thing on my enlarger would dim for about a half-second. A power conditioner would take care of that problem, but my solution was to just put them on two different circuits.

Steve Smith · Jun 25, 2011

Hammond organs have tone wheels driven by synchronous motors. These might now be slightly out of tune (more than normal!). The organ was designed using motor technology Hammond developed for electric clocks.

http://en.wikipedia.org/wiki/Hammond_Clock_Company

Steve.

ic-racer · Jun 25, 2011

Actually there are many darkroom items that can be affected, but as pointed out the effects will not be detected.

Some examples: The ECU1840 controller for the Durst L1840 times off the mains and the power supply needs to be set to 50 or 60 Hz for proper operation. The signal is carried through the ribbon cable on one of the outermost wires, so if the enlarger runs over the cable, the timer can go out (ask me how I know...). Also, zero crossing detectors are used for timing in the main lamp regulation circuit but small frequency shifts should not make any difference to that circuit. The Omega D5500 uses a 6MHz crystal for timing so it would not be affected.

As mentioned the Wejex sensitometer uses a stepper motor, as do the Graylab 300 series timers.

BetterSense · Jun 25, 2011

. Another way of doing timing stuff would be a microcontroller of some sort, but those generally also have set clock frequencies that are pretty much entirely independent of current and voltage

All microcontrollers I know of have either crystals or RC resonators to get them going. In both cases the supply voltage doesn't matter, it just has to be enough and not too much.

Does anyone know anything about Technics turntables? The one in my avatar has a strobe light that you can use to adjust the platter speed, but I don't know if it syncs off the mains or not, and I also don't know if the mains frequency changing would cause the turntable speed to change.

MattKing · Jun 25, 2011

BetterSense said:
All microcontrollers I know of have either crystals or RC resonators to get them going. In both cases the supply voltage doesn't matter, it just has to be enough and not too much.

Does anyone know anything about Technics turntables? The one in my avatar has a strobe light that you can use to adjust the platter speed, but I don't know if it syncs off the mains or not, and I also don't know if the mains frequency changing would cause the turntable speed to change.

I bet the Technics turntable has different speed synch marks for 50 Hz and 60 Hz power, so I would guess that it does synch off the mains.

ic-racer · Jun 25, 2011

Many turntables just have a simple neon lamp for setting the speed of the platter. This blinks with the mains frequency. I notice on my Technics, the light is RED rather than neon orange, but either way, it blinks with the mains frequency.

Crashbox · Jun 25, 2011

I'm not at all happy about this tolerance loosening- I have two old IBM/Simplex school clocks circa 1960 which (because of accurate frequency regulation) are indeed very accurate. Granted, NIST atomic clocks put these in the dust, but I like them

BetterSense · Jun 25, 2011

Many turntables just have a simple neon lamp for setting the speed of the platter. This blinks with the mains frequency.

Well, see this is where I'm going. If the neon strobe blinks with the mains frequency, and the turntable's speed itself is proportional to the mains frequency, then if the mains frequency changes down say 10%, then the strobe will strobe 10% slower and then maybe the turnable itself will spin 10% slower so I will not actually be able to tell except the music might sound funny. I doubt I would actually be able to tell because I used to have a much cheaper Marantz turntable with a synchronous motor, and it was 4% slow, and you really couldn't tell.

ic-racer · Jun 25, 2011

BetterSense said:
Well, see this is where I'm going. If the neon strobe blinks with the mains frequency, and the turntable's speed itself is proportional to the mains frequency, then if the mains frequency changes down say 10%, then the strobe will strobe 10% slower and then maybe the turnable itself will spin 10% slower so I will not actually be able to tell except the music might sound funny. I doubt I would actually be able to tell because I used to have a much cheaper Marantz turntable with a synchronous motor, and it was 4% slow, and you really couldn't tell.

Yes that is correct, but the deviation in mains frequency is only going to go up to 0.004% in some parts of the country. Only the vinyl audiophiles with oxygen-free hookup wire neatly arranged at right angles will be disturbed by the news. (they won't be bothered by this if they don't know about it ).

Most DVMs should have a frequency counter. I just checked my mains and I get a steady 122.7V and 60.00 Hz.

There is already a similar thread to this one on "audiokarma.org" http://www.audiokarma.org/forums/showthread.php?t=377658&highlight=mains+frequency

Nicholas Lindan · Jun 26, 2011

The strobe on turntables is usually a neon bulb syncing to the line frequency. However, the turntable itself, if it is modern, would run off a quartz crystal. When the table was designed the line frequency strobe was a check on the operation of the crystal and motor - now the table's crystal and platter motor are a check on the operation of the power grid...

The article states a 20min/year error, but also a 14 seconds / day error. The daily error is about 0.02% - and quite irrelevant for any photographic purpose. An untrimmed bog-standard quartz microprocessor crystal can have an initial tolerance of 30ppm or 0.003% - about the same as the proposed sloppy power line timing.

I would say, though, that the 14 minutes a year is a pain in the but when it comes to resetting clocks, but then power failures mean the clocks need resetting several times a year anyway. Old analog electric clocks will be a bother, but I only have one of those left.

Steve Smith · Jun 26, 2011

Nicholas Lindan said:
The strobe on turntables is usually a neon bulb syncing to the line frequency. However, the turntable itself, if it is modern, would run off a quartz crystal.

Yes, otherwise, if the motor was also synchronous to the mains frequency, it would always be correct to the strobe and you wouldn't be able to adjust it.

Steve.

Power Grid Change May Disrupt Clocks in USA

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