Power Grid Change May Disrupt Clocks in USA
AP EXCLUSIVE: Power grid change may disrupt clocks
By Seth Borenstein, Associated Press Science Writer, via Yahoo! News, June 24, 2011
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.
Last edited by Ken Nadvornick; 06-24-2011 at 05:12 PM. Click to view previous post history.
"Take her to sea, Mister Murdoch. Let's stretch her legs."
The First Officer then reaches out and confidently rings the engine room telegraph over to ALL AHEAD FULL...
— Captain Edward John Smith to First Officer William Murdoch, on the bridge of the RMS Titanic, 11 April 1912
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.
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.
i use the sun, not the clock
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.
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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.
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%.
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.
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.
Last edited by Steve Smith; 06-25-2011 at 06:35 AM. Click to view previous post history.
"People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.
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.