Metso Automation
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278705
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Chapter 8
IRIG-B Interface
Overview
IRIG-B is an international time signal standard. Many vendors sell very
accurate clocks that generate IRIG-B signals. IRIG-B is also available as an
output from many GPS satellite receivers. Such IRIG time signals are
typically accurate to within microseconds.
The maxDPU4F is available with an optional IRIG-B input (models PDP406
and PDP408, DPU assembly #181551). These DPUs have a BNC connector
through which the IRIG-B signal is applied and internal circuitry to decode
the signal. Once it decodes the signal, the DPU uses it as the basis for its
internal clock. Normally, the IRIG DPU is assigned the roll of a Time
Master (via a database setting) and it broadcasts the accurate time to the rest
of the DPUs, DBMs and direct access workstations in its domain. In this
way, the entire domain can be synchronized to an accurate clock.
The IRIG signal should be applied to both the primary and secondary of a
maxDPU4F pair to provide a redundant time source should one of the DPUs
fail.
The IRIG-B (B122) time signal is an amplitude modulated 1KHz sine wave.
Figure 1 shows a portion of a typical waveform. V1 and V2 represent the
peak-to-peak amplitudes of the two modulation levels.
Figure 1. IRIG-B Waveform
Summary of Contents for PDP 400 maxDPU4F Series
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