Specifications

RN: 5-91
RS3: Software Release Notes for P1 R4.2
Changes to RS3 Manuals
A DC Distribution Bus should have not less than two and no more than
five power supply modules wired to it. This requires the use of 1--3
System Power Supply Units. T here must always be one power supply
module more than required to supply the load. The additional module is
redundant and serves as a backup in case one of the other modules
fails. This is referred to as N+1 redundancy.
Although a power supply module has a maximum output rating of 46
amperes when operating singly, the RS3 system requires redundancy,
either with a power supply, a bus, or both. When outputs are wired in
parallel to form a bus, the maximum output rating of each power supply
module is 43 amperes. If the power supply modules are loaded beyond
the maximum rating, they will enter a cyclic on-off mode at about a 1 Hz
rate. When more than one module is connected to the same DC
Distribution Bus, they load-share within 10 percent of each other. This
tolerance reduces the maximum planned loading for each power supply
module to 43 amperes. Reducing the output rating of the m odules helps
prevent any of them from unnecessarily entering an over-current
condition, especially during power-up.
The maximum planned load for an A/B Bus configuration is 172
amperes. T his requires four power supply modules plus one more for
redundancy. The fifth module delivers the required load if one of the
other modules fails. Table 1.2.3 shows the maximum loads that can be
supplied with various numbers of power supply m odules used with a DC
bus configuration.
This configuration is a good solution when powering devices that cannot
accept a separate redundant power input. It requires fewer power
supply modules than the redundant bus or redundant bus/redundant
power supply configurations.
NOTE: If a single System Power Supply Unit (two power supply
modules) is used, the configuration should be the standard A/B
distribution shown in Figure 1.2.7. Buses A and B are jumpered
together and operate in a series.
Redundant Bus Configuration
A redundant bus configuration is beneficial when redundancy at the DC
Distribution Bus level is desired. All Fisher-Rosemount manufactured
devices powered from the DC distribution panel have redundant DC
input capability. If either Bus A or Bus B fails, the r emaining bus ensures
that power will continue to be supplied to the devices.
BusBPowerProvidedbytheUser:
Figure 1.2.8 represents a redundant DC power distribution
configuration. Note that Bus A and Bus B are not connected together. In
this configuration, each of the two buses must be capable of providing
the full load, independent of each other. One or more power supply