The V-400A series clocks can be synchronised from many different external sources, including radio and satellite time signals, together with various time codes and impulse signals.
The principle advantage of systems which use a time code rather than an impulse signal for controlling a network of slave clocks are
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The time code enables the slave clock to automatically self-setting to the correct time on installation, following failures of the mains power supply or in the event of system maintenance.
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Seasonal time changes will normally take place within a few seconds, rather than at the delayed rate typical of an impulse system.
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The slave clocks will not, in normal circumstances, show an incorrect time due to missed impulses.
w482® Time Code
The w482® signal has been developed for controlling electronic clocks, using a single cable pair data interconnection, in electrically noisy environments and over considerable distances.
A unique feature of the w482® time code format is the ability to control slave clocks or time zone displays showing time in up to fifteen different synchronised time zones using a simple low-specification single cable pair.
The w482® signal is transmitted at 4-24v amplitude and at 50 bits per second data rate. The signal is virtually immune from electro-magnetic interference.
Up to 100 slave clocks can be controlled by a single unbuffered 482 master clock at distances of up to several km.
A 400A series clock fitted with a 404.M local master code output module, may be also used as a master clock in a small clock system. Up to ten other 400A series slave clocks may be controlled, displaying time in a single time zone, at distances of up to 400m.
Alternate & Single Polarity Impulses
The majority of conventional analogue slave clocks are controlled by impulse master clock systems using alternate polarity impulses of 24v amplitude.
Impulses, typically of one half to one second duration, may be sent every second, every half minute or every minute depending on the clock mechanism. The transmission of impulses is either stopped or speeded up to effect seasonal or other time corrections. The slave clocks are connected in parallel across the signal cable from the master clock.
Some older systems use higher impulse voltages of up to 60v. Other systems use single polarity impulses, series interconnection of the slave clocks and 'hourly correction' pulses. V-400A series digital clocks , calendar clocks and time zone displays may be programmed to be synchronised by both single and alternate polarity impulses at a one second, half minute or one minute repetition rate providing that the impulses are from 6-48v amplitude and intended for parallel connection.
An optional internal 404.S interface module is available to enable 400A clocks and calendar clocks to be used with series impulse applications. V-400A series units may be operated from 60v alternate polarity signals if a 3K3 1W resistor is fitted in series with the clock across the signal line.
Standard V-400A clocks will NOT operate correctly when connected to 'hourly correction' systems.
EBU/SMPTE Time Code
EBU/SMPTE time code is used in broadcast applications for 'stamping' time information on recordings and for the control of clocks and other intelligent systems. EBU time code is used in PAL and SECAM applications at 25 frames per second. SMPTE is the American standard for use with 30fps NTSC systems.
The signal data is 2000 bits per second for SMPTE with each frame of data comprising 80 bits.
The EBU standard defines the format for hours, minutes and seconds information. Date information can be added to the signal in a number of formats within 'user bit' areas.
400A series clocks fitted with the 404.E internal interface module may be programmed to decode the two most popular date formats for either EBU or SMPTE code transmitted within +/-20% of the standard speed.
When using 400A series calendar clocks synchronised by EBU/SMPTE time code, please ensure that the EBU date code format is compatible with the 400A calendar clock.
IRIG-B/AFNOR NFS 87 500
IRIG-B is one of a series of time codes originally developed in the 1940s by the international Range Instrumentation Group (IRIG) for recording time information on magnetic tape and wire for rocket test range instrumentation purposes. IRIG-B code is normally transmitted at a 100Hz bit rate amplitude modulated on a 1KHz carrier, where the amplitude of a '1' bit is three times that of an '0' bit.
The IRIG-B code contains day-of-year and hours, minutes and seconds information. AFNOR NFS 87 500 time code is a development of IRIG-B which is widely used in Europe and contains additional day, day-of-month and year information.
All 400A clocks and calendar clocks may be synchronised with either IRIG-B or AFNOR NFS 87 500 time code when fitted with the optional 404.I internal interface module.
RS232 & RS485 (RS422)
RS232 and RS485 are international standards for the transmission of information, usually as ASCII characters, between intelligent equipment.
RS232 is intended for short distance transmission, using un-balanced lines, between one master and one slave. The latest standards specify a maximum driven capacitance of 2500pF rather than a specific line length and it is usually possible, at lower data rates, to control several slave units within a small area.
RS485(RS422) is intended for use in multi-slave applications using a balanced line. A single master will control up to 32 slaves, using a correctly terminated single twisted pair cable, at distances up to 1000m. The earlier RS422 standard may be regarded as interchangeable with RS485 except for a limit of 10 slaves.
The 404.2(RS232) and 404.4(RS422/485) internal interface modules for the 400A series clocks and calendar clocks allow either:
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The remote setting or synchronisation of 400A series clocks by computers using one of three data formats.
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The transmission of a serial ASCII time message, either every second or 'on demand', in one of seven data formats.
The 'on demand' mode may be triggered by the receipt by the clock of an ASCII character (RS232 only) or by the closure of an external voltage free switch connected to the clock.
Each message may be transmitted or received at 1200, 2400, 4800 or 9600 baud, seven or eight data bits and at odd or even parity.
It is very important that both the 400A series clock and the connected computer or other equipment are using the same signal standard, recognise the data format and are set to the correct baud rate, bit length, parity and number of stop bits.
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