Slave clock
Encyclopedia
In telecommunication
, a slave clock is a clock
that is coordinated with a master clock
. Slave clock coordination is usually achieved by phase
-locking the slave clock signal
to a signal received from the master clock. To adjust for the transit time
of the signal from the master clock to the slave clock, the phase of the slave clock may be adjusted with respect to the signal from the master clock so that both clocks are in phase. Thus, the time markers of both clocks, at the output
of the clocks, occur simultaneously.
In other areas, the term refers to satellite electrical clock
s that operate remotely from an electrical pulse issued by a master clock
. In the 19th and early 20th centuries, slave clocks were widely used throughout public buildings and business offices, and their remote operation was regulated by electrical signals sent by a centralized master clock.
These older styles of slave clocks either keep time by themselves, and are corrected by the master clock, or require impulses from the master clock to advance. Many slave clocks of these types remain in operation, most commonly in schools.
in the late 1940s. IBM sold their time division to the Simplex Time Recorder Company in 1958. The methods & clock mechanisms have remained basically unchanged, other than appearance and style over the years. Today, this same protocol is used by several manufacturers, including Latham, Dukane, Cincinnati and Standard Electric Time. Digital master clocks have replaced older mechanical types.
All consist of a master clock and a number of secondary clocks in remote locations. These secondary clocks appear to run like an ordinary plug-in electric clock and run on their own synchronous electric motor and will maintain correct time unless there is an interruption in electric service, depending on the master clock only for the periodic synchronizing impulse. These clocks differ from the ‘impulse’ type, which are electrically advanced each minute by the master clock. Impulse type clocks are usually called ‘slave’ clocks since they cannot function at all without the master clock.
There are two basic variations in synchronous systems, ’wired’ and ‘electronic’.
In a wired system, the secondary clocks are ‘hard-wired’ to the master clock with their own network of wiring. This dedicated wiring consists of 3 wires and requires that all secondary clocks be connected to this network in order to receive corrections from the master clock. These systems are usually 110 volts but some are 24 volts. The master clock energizes the third wire to apply voltage to the correction solenoids
(called ‘clutch magnets’ by the manufacturer) in the secondary clocks.
In an electronic system, the correction impulse is applied to the normal building wiring, in the form of a high-frequency audio signal (typically 3510 Hz) applied to the normal 60 Hz frequency of the electrical system. Special receivers in the secondary clocks receive this impulse & apply voltage to the correction solenoid. In this type system, secondary clocks need no special wiring & may be plugged into any 110 volt outlet in the building.
The cycle can also be initiated manually for testing & adjustment as follows:
With clock running, rotate 90 degrees to the right, so that the ‘9’ is at the top. Hold in this position approximately 8 seconds (you may hear a clicking sound during this time), then return the clock to its normal upright position. Within 60 seconds, the hands will slowly advance to the next hour as described below in the third paragraph under ‘Hourly Correction’.
The actual correction that follows is the same in both types of systems. The only difference (described above) is the method by which the correction solenoid is energized.
The correction cycle lasts precisely 60 seconds, ending at 59 minutes 0 seconds at which time, all clocks in the system will display the same time as the master clock.
The cycle causes an internal clock-wise sweep, beginning at the 59 minute position and takes 60 seconds, rotating around the dial, ending at the 59 minute position. During this sweep, if the minute hand is not in proper position, when the sweep rotation reaches it, the minute hand is slowly rotated at 1 rpm until it reaches the 59 minute mark. At this point it is now in sync with the master clock.
During the cycle, the red second hand continues its normal 1 rpm motion but is held in place when it reaches the 60 second mark. It is released when the cycle is complete (minute hand reaches 59 minutes) and now minutes and seconds are both in sync with the master clock.
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
, a slave clock is a clock
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...
that is coordinated with a master clock
Master clock
A master clock is a precision clock that provides timing signals to synchronize slave clocks as part of a clock network. The master clock in such installations is controlled by an accurate quartz crystal oscillator, usually referenced to an external frequency standard such as MSF, which is part of...
. Slave clock coordination is usually achieved by phase
Phase (waves)
Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...
-locking the slave clock signal
Clock signal
In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome to coordinate actions of circuits...
to a signal received from the master clock. To adjust for the transit time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
of the signal from the master clock to the slave clock, the phase of the slave clock may be adjusted with respect to the signal from the master clock so that both clocks are in phase. Thus, the time markers of both clocks, at the output
Output
Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...
of the clocks, occur simultaneously.
In other areas, the term refers to satellite electrical clock
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...
s that operate remotely from an electrical pulse issued by a master clock
Master clock
A master clock is a precision clock that provides timing signals to synchronize slave clocks as part of a clock network. The master clock in such installations is controlled by an accurate quartz crystal oscillator, usually referenced to an external frequency standard such as MSF, which is part of...
. In the 19th and early 20th centuries, slave clocks were widely used throughout public buildings and business offices, and their remote operation was regulated by electrical signals sent by a centralized master clock.
These older styles of slave clocks either keep time by themselves, and are corrected by the master clock, or require impulses from the master clock to advance. Many slave clocks of these types remain in operation, most commonly in schools.
Synchronous Systems
This type system was developed by IBMIBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
in the late 1940s. IBM sold their time division to the Simplex Time Recorder Company in 1958. The methods & clock mechanisms have remained basically unchanged, other than appearance and style over the years. Today, this same protocol is used by several manufacturers, including Latham, Dukane, Cincinnati and Standard Electric Time. Digital master clocks have replaced older mechanical types.
All consist of a master clock and a number of secondary clocks in remote locations. These secondary clocks appear to run like an ordinary plug-in electric clock and run on their own synchronous electric motor and will maintain correct time unless there is an interruption in electric service, depending on the master clock only for the periodic synchronizing impulse. These clocks differ from the ‘impulse’ type, which are electrically advanced each minute by the master clock. Impulse type clocks are usually called ‘slave’ clocks since they cannot function at all without the master clock.
There are two basic variations in synchronous systems, ’wired’ and ‘electronic’.
In a wired system, the secondary clocks are ‘hard-wired’ to the master clock with their own network of wiring. This dedicated wiring consists of 3 wires and requires that all secondary clocks be connected to this network in order to receive corrections from the master clock. These systems are usually 110 volts but some are 24 volts. The master clock energizes the third wire to apply voltage to the correction solenoids
(called ‘clutch magnets’ by the manufacturer) in the secondary clocks.
In an electronic system, the correction impulse is applied to the normal building wiring, in the form of a high-frequency audio signal (typically 3510 Hz) applied to the normal 60 Hz frequency of the electrical system. Special receivers in the secondary clocks receive this impulse & apply voltage to the correction solenoid. In this type system, secondary clocks need no special wiring & may be plugged into any 110 volt outlet in the building.
The cycle can also be initiated manually for testing & adjustment as follows:
With clock running, rotate 90 degrees to the right, so that the ‘9’ is at the top. Hold in this position approximately 8 seconds (you may hear a clicking sound during this time), then return the clock to its normal upright position. Within 60 seconds, the hands will slowly advance to the next hour as described below in the third paragraph under ‘Hourly Correction’.
The actual correction that follows is the same in both types of systems. The only difference (described above) is the method by which the correction solenoid is energized.
Hourly Correction
The correction impulse is issued by the system master clock at 57 minutes 54 seconds after each hour and lasts for 8 seconds (until 58 minutes 02 seconds). The correction solenoids in the secondary clocks are energized by this pulse. This causes the attached armature and cam to engage a gear and rotate upwards to lift a latch allowing the correction cycle to begin. This takes 6 seconds and causes the secondary clocks to begin their correction cycle at precisely 58 minutes 0 seconds.The correction cycle lasts precisely 60 seconds, ending at 59 minutes 0 seconds at which time, all clocks in the system will display the same time as the master clock.
The cycle causes an internal clock-wise sweep, beginning at the 59 minute position and takes 60 seconds, rotating around the dial, ending at the 59 minute position. During this sweep, if the minute hand is not in proper position, when the sweep rotation reaches it, the minute hand is slowly rotated at 1 rpm until it reaches the 59 minute mark. At this point it is now in sync with the master clock.
During the cycle, the red second hand continues its normal 1 rpm motion but is held in place when it reaches the 60 second mark. It is released when the cycle is complete (minute hand reaches 59 minutes) and now minutes and seconds are both in sync with the master clock.