AR (later AR-3) System - "Automatic Resetting" clock system. Initially running off a pendulum based master clock like the series clocks, later off of synchronous motored masters and later electronic master clocks, the AR/AR-3 system has three wires going to the slave clocks. An impulse system, these clocks received an impulse on the "third" wire at the 58th minute and 50th second (at least on the Standard Electric Time MTP 1400), causing the mechanism to disengage, and making the minute hand swing up to the 59th minute by gravity, correcting any clock up to 25 minutes fast or slow. See the bulletin accessible from the main page. This clock can run without correction at all, contrary to documentation that says the clock requires an impulse on the third wire to get to the 59th minute. This is not true, it can run just like the series clocks do without correciton.
The "proper" correction method for the AR3, per the original design, is for the master clock to send out a correction impulse on the 3rd wire, generally from the 10th to the 17th or so second. I currently have a Linux computer replicating this and my AR3 clocks work beautifully this way.
AR-2 System - works much like the AR/AR-3 system, except with two wires. At the 58th minute and 50th second, 48VDC is sent out (instead of 24VDC), causing the mechanism to go into "correction" mode.
AR-2A System - identical to the AR-2 system, except the correction impulse is a minute later (at the 59th minute and 50th second).
Bellboard - a device usually found near the master clock, which has "columns" and "rows" comprised of pegs and holes. Each row is classroom or other room, each column is a bell circuit from the master clock. A peg in the corresponding hole will cause the bell to ring according to that circuit's schedule in the indicated classroom. Also contains a push button to manually ring the bell or buzzer in that particular room.
Impulse System- This type of clock DOES NOT have the ability to keep time on its own. The mechanism contains a magnet, a ratchet and an assortment of gears. Once a minute, it receives a 1 to 3 second (modern systems tend to use a two second impulse) long impulse from the master clock, activating the mechanism. When the power is disengaged, the magnet releases the ratchet, causing the hands to advance once minute. Typically used in older schools, though there are schools still installing these systems. Usually more cost effective than synchronous systems.
Master Clock - The clock usually found in the main office of a school or factory. For the most part, the only true "time-keeper" in a master-slave clock system. This guy sends out electrical impulses, on the minute or hour depending on the set up, advancing or correcting the clocks in classrooms and other areas of the buildings. Also rings the bells for class changes, etc.
Series System - The original type of Standard Electric Time impulse system. A self-winding, pendulum based master clock kept time and sent impulses out once a minute, for about 1/2 second. The power for these impulses came from batteries in or near the master clock. The voltage on these clocks at the actual clock were about 1.8VDC at 200mA. The clocks were wired in "series" (as opposed to "parallel"). If one clock in the circuit became disconnected, all the clocks stopped. The voltage at the master clock was dependent on the number of clocks in the circuit.
Slave Clock - The clock usually found in classrooms, the cafeteria and other rooms of the school or factory. Receives impulses from the master clock to keep time. See impulse system and synchronous system.
Synchronous System - This type of clock system is characterized by the sweep second hands on the slave clocks. These clocks can pretty much keep time on their own, however, they receive impulses hourly and on the 12-hour to correct themselves to the master clock. (After power outages, daylight savings time, etc.)
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