10 ms·
Made me think about the Swiss Railways clock that has the second hand completing the circle in 58.5 seconds; all the clocks on the network then wait for the syn
by agys 4y ago
Made me think about the Swiss Railways clock that has the second hand completing the circle in 58.5 seconds; all the clocks on the network then wait for the sync signal from the “master clock".
https://en.wikipedia.org/wiki/Swiss_railway_clock https://en.wikipedia.org/wiki/Swiss_railway_clock
- mprovost 4y agoI love those clocks! But from memory, the second hand gets "stuck" at 12 and then when it moves again, the minute hand advances at the same time. On this one, the minute hand jumps forward at the same time that the second hand goes to 12.
- d1sxeyes 4y agoThe second hand is supposed to go round the clock in 58.5 seconds, and then 'wait' for a synchronisation signal before starting off for the next minute.
- capableweb 4y agoThe animated example in https://en.wikipedia.org/wiki/Swiss_railway_clock#/media/File:SBB_railway_clock_animated.gif https://en.wikipedia.org/wiki/Swiss_railway_clock#/media/Fil... seems to have the first behavior you mention, it get stuck at 12, minute hand increments and then the second hand starts moving again after the minute hand movement.
- jcrawfordor 4y agoBoth systems could be found. Early to mid 20th-century master clock systems were pretty much all designed around a common theme but there were many variations. Some secondary clocks even used fully free-running second hands that weren't synchronized at all and so had no relation to the minute hand advancement.
- jedberg 4y agoThe clocks in my elementary, middle, and high schools would do something similar. Not every minute, but every hour. At the top of the hour, when there was 15 seconds left, the second hand would make 3 second jumps until it hit the top, and then hold until the next hour started. I always thought that was a brilliant way to keep mechanical clocks in sync. And the system had been there since the 1970s, so it was well before digital clocks were feasible for a school.
- smm11 4y agoOur elementary school clocks (70s) made a variety of nearly imperceptile sounds as they got near the top of the hour, or turned it over. We were like dogs when they hear the about-to-eat sounds start.
- woleium 4y agoPavlov was sitting in a bar when the last order bell rang. "Oh shoot! I need to feed the dogs" he thought.
- bmitc 4y agoHow did they know when the next hour started without digital communication?
- jcrawfordor 4y agoThe details depended on the system. The most common arrangements were either polarity (hour pulse opposite polarity of minute pulse) or a separate wire for hour pulse. Later systems introduced serial digital communications but were never as widely installed as the minute and hour pulse systems in schools.
- jedberg 4y agoThey had digital communication just not cheap ICs. I don't know how it worked but I imagine it was something like a mechanical switch that held the minute hand until it got a signal from the main office to start moving again. The clocks could even be set for Daylight time centrally, so I assume it had a way to send a signal that triggered a motor to move the hour hand faster.
- tdeck 4y agoSince it's a school I wonder if they could just hold them back 1 or 11 hours on the weekend for DST changes. This would eliminate the need for an additional signal and circuitry on each follower clock.
- 4y ago
- noja 4y agoWhy 58.5 seconds?
- doublesocket 4y agoBecause then any slow clocks have 1.5 seconds to receive additional pulses from the master clock to bring them into sync.
- jonsen 4y agoThere are no additional pulses. Only minute pulses. It's a motor driving the second hand. The motor starts by the minute pulse and stops itself when reaching the top.
- dheera 4y agoTo deal with any inconsistencies in the speed at which they complete the 58.5 seconds. If a particular defective clock takes 59.9 seconds instead of 58.5 it'll be just fine, as it will start going again when it gets the next minute pulse from the central system.
- spyremeown 4y agoAll clocks from Deutsche Bahn stations are also like this. It's always very amusing.
- eknkc 4y agoThey are available as desk and wristwatches too (https://mondaine.com https://mondaine.com)