Author Topic: Why do the clocks in my school make a loud motor noise every hour?  (Read 5553 times)
Rommie
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #15 on: October 05, 2019, 01:44:21 PM » Author: Rommie
When I visited the studios at BBC Radio 2 in London a few years ago, I noticed that the clocks on the desks have a manufacturer's name plate on the back which amongst other things mentions that the device is a "Time Indicating Appliance"  ???

As if we didn't know that, why on earth they didn't just call it a clock is beyond me. Nobody I asked seemed to know the reason either  ::)
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sol
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #16 on: October 05, 2019, 09:40:50 PM » Author: sol
I have one of those clocks but I need to make a circuit that simulates the correction pulse.



I your clocks have a 120V coil and 120V motor, you only need a digital timer with 'school bell' function where it will turn on for x seconds at the set points. It will not be the most accurate long term, but it will certainly work. I worked in a school with such clocks, and they had one of those digital timers in the office. It was a multi channel one, and was used to trigger the bell relay in the intercom system as well as synchronizing all the clocks. The clocks (and bell) weren't exact to the world's atomic clocks, but at least they displayed the same time as the school bell.

If your clocks have a different voltage for the coil, you can use the same clock I mentioned, but wire in an appropriate step down transformer.
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Wireman
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #17 on: July 23, 2020, 01:08:11 AM » Author: Wireman
You have a synchronized clock system. A small solenoid is energized every hour to correct the minute hand (=to make sure it is accurate). The electrical pulse is usually about 2-3 seconds long. This happens at the 58 or 59 minute mark (depending on system configuration). Then, usually at 5:58, a longer pulse of about 6-7 seconds occurs, and that corrects the hour hand. What happens with the long pulse, it "binds" temporarily the minute hand with the second hand until all hands read 5:58. Notches on wheels align at 5:58 (one wheel for each hand) and released the minute and seconds hands and the clock continues to operate normally.

Now, if a power outage occurs, you might have to wait until 5:58 for a correction because the window of opportunity for the hourly correction is in the order of a few minutes on some systems, and the correction of the hour hand is only twice daily. If you get a power outage at 6:00 and the clock is stopped for 11 hours and 55 minutes, for example, the next correction will need to make the minute hand rotate twelve times, which takes twelve minutes. You will then miss the hourly correction, and if the minute hand is too far from the "window", you have to wait until the next 5:58 for a better correction.

This system is all mechanical and electric. There are no complicated computers originally. Nowadays, they are typically used with a master clock that is electronic as the mechanical versions are too difficult to maintain, parts are difficult to source and all that jazz.

You most likely have a 3-wire system, where you have a hot and neutral (120V) for the clock motors, and a second hot (also 120V) for the solenoid. The second hot is only energized during the correction pulse.

Hope this helps.
Thank you for clearing all that up. It was a HUGE help! The school I went to back in the 80s had clocks that did this and I always wondered what that was about.
Now if only I could figure out what that WEIRD LOUD NOISY chute was that we dumped our heavy cardboard-like lunch trays down???? I think it grinded them up and it kind of looked like there was a large basin of water in there?? VERY STRANGE!! The school was built in 1974 and it had some great lighting when you compare it with what's out there today.
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Fluorescent05
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #18 on: July 23, 2020, 11:55:50 AM » Author: Fluorescent05
Thank you for clearing all that up. It was a HUGE help! The school I went to back in the 80s had clocks that did this and I always wondered what that was about.
Now if only I could figure out what that WEIRD LOUD NOISY chute was that we dumped our heavy cardboard-like lunch trays down???? I think it grinded them up and it kind of looked like there was a large basin of water in there?? VERY STRANGE!! The school was built in 1974 and it had some great lighting when you compare it with what's out there today.
What did the chute look like? Did you put food waste and other garbage or only the trays down the chute?
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Wireman
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #19 on: July 23, 2020, 12:22:19 PM » Author: Wireman
What did the chute look like? Did you put food waste and other garbage or only the trays down the chute?
The opening to the chute was rectangular kind of like a long shoebox.
Absolutely NO food waste of any kind could go in the chute especially the plastic forks and spoons. Milk cartons couldn't go down the chute either. I'd sure like to find out what this noisy beast was??
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Fluorescent05
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #20 on: July 23, 2020, 02:16:15 PM » Author: Fluorescent05
The opening to the chute was rectangular kind of like a long shoebox.
Absolutely NO food waste of any kind could go in the chute especially the plastic forks and spoons. Milk cartons couldn't go down the chute either. I'd sure like to find out what this noisy beast was??
What exactly did it sound like?
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Wireman
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #21 on: July 23, 2020, 04:02:04 PM » Author: Wireman
What exactly did it sound like?
It was a very loud rumbling sound. As if a freight train was going to come through the wall!
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Fluorescent05
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #22 on: July 23, 2020, 04:37:14 PM » Author: Fluorescent05
It was a very loud rumbling sound. As if a freight train was going to come through the wall!
Google did not turn up any search results, however I'm guessing the lunch trays were some sort of biodegradable material that got ground up and the water would dissolve it. How much water was down there? Did they only turn it on at the end of lunch?
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Wireman
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #23 on: July 23, 2020, 05:06:44 PM » Author: Wireman
Google did not turn up any search results, however I'm guessing the lunch trays were some sort of biodegradable material that got ground up and the water would dissolve it. How much water was down there? Did they only turn it on at the end of lunch?
What you said sounds right to me. The machine kept running as the different classes took turns in the cafeteria. There was quite a bit of water in there! I remember seeing ground up pieces coming out of another chute behind the building into a special dumpster of some kind. Of course this was long before today's environmental awareness. It was an old building full of electrical oddities besides clocks that adjust themselves and machines that ate lunch trays. This 80,000 square foot building was also full of F40 T12 lamps on 277 volt ballasts!
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Fluorescent05
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #24 on: July 23, 2020, 05:23:39 PM » Author: Fluorescent05
What you said sounds right to me. The machine kept running as the different classes took turns in the cafeteria. There was quite a bit of water in there! I remember seeing ground up pieces coming out of another chute behind the building into a special dumpster of some kind. Of course this was long before today's environmental awareness. It was an old building full of electrical oddities besides clocks that adjust themselves and machines that ate lunch trays. This 80,000 square foot building was also full of F40 T12 lamps on 277 volt ballasts!
The lights sound awesome! Were the ground up pieces wet when coming out of the chute? Otherwise, what would be the point of the water?
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Wireman
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #25 on: July 23, 2020, 05:43:07 PM » Author: Wireman
The lights sound awesome! Were the ground up pieces wet when coming out of the chute? Otherwise, what would be the point of the water?
I'm really not sure if they were wet or not but no water ever came out of the chute. Still I don't know why water would be needed anyway. As far as the lights go the parking lot was lit up with trunnion mount floodlights with coated MV lamps. The baseball field had dozens of floodlights with coated 1000w MV lamps that were eventually replaced with clear MH retrofit lamps.
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Fluorescent05
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #26 on: July 23, 2020, 10:27:30 PM » Author: Fluorescent05
I'm really not sure if they were wet or not but no water ever came out of the chute. Still I don't know why water would be needed anyway. As far as the lights go the parking lot was lit up with trunnion mount floodlights with coated MV lamps. The baseball field had dozens of floodlights with coated 1000w MV lamps that were eventually replaced with clear MH retrofit lamps.
Is the school still there?
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Wireman
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #27 on: July 23, 2020, 11:00:26 PM » Author: Wireman
Is the school still there?
Yep Nob Hill elementary school is still very much there. Same original building just a few cosmetic upgrades over the years. It's still considered the best in my hometown of Sunrise and one of the best in Broward County.
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Wireman
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Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #28 on: July 23, 2020, 11:37:42 PM » Author: Wireman
The clocks on the synchronized system were made by Simplex. The school also had some old and crazy looking fire horns that may have been made by Simplex or Faraday. I might be able to get a picture.
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Fluorescent05
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Zack


Re: Why do the clocks in my school make a loud motor noise every hour? « Reply #29 on: July 24, 2020, 01:40:29 AM » Author: Fluorescent05
Yep Nob Hill elementary school is still very much there. Same original building just a few cosmetic upgrades over the years. It's still considered the best in my hometown of Sunrise and one of the best in Broward County.
Is the rumbling chute still there?
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