144 Options List
C.14 Option 23, COMTRADE Sample Rate Generator
C.14.1 General Description
When equipped with the Option 23 COMTRADE Sample Rate Generator, the Satellite-Controlled
Clock generates any one of the 48 standard sampling rates for waveform digitization in 50 or 60
Hz systems which are defined in IEEE Standard C37.111-1991, Data Exchange (COMTRADE) for
Power Systems. Standard COMTRADE Sampling Rates are listed in Tables 1 and 2 (on following
page).
The selected sample rate is available as a 5 V CMOS-level square wave in both normal (rising edge
of clock synchronous with 1 PPS) and complemented (falling edge of clock synchronous with 1 PPS)
polarities. The sampling pulse is synchronized to within 50 ns of 1 PPS, and has sample-to-sample
jitter less than 1 ns.
C.14.2 Principles of Operation
The Option 23 assembly generates sampling signals, which are precisely locked to 1 PPS-GPS by
phase locking a precision voltage-controlled crystal oscillator (VCXO) to the internal 1 kPPS signal
present in the clock. This VCXO output signal is then divided down to obtain the desired sampling
rate. Synchronization logic is also provided, to ensure that the output divider is synchronized to
1 PPS-GPS. By using a precision VCXO, pulse-to-pulse sampling jitter is held to an absolute
minimum, and is specified not to exceed 1 ns rms. The output signals have a 50% duty cycle
(square wave).
C.14.3 Other Features
The Option 23 assembly includes four configurable BNC outputs, which are in addition to those
available for the standard model clock. Either normal or complemented-polarity COMTRADE
sampling frequency signals may be made available at each of these additional outputs. Furthermore,
any output not configured for a COMTRADE sampling rate output can be used as a general-
purpose configurable output, and can deliver any of the 21 standard signals available in the Model
1084A/B/C. The Option 23 assembly may be installed in the standard option slot available (Slot
B).
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