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Dual-host Redundant Data Acquisition System for
MOXA Async Server
MOXA CN2500 Async Server is an advanced and reliable serial-to-Ethernet
device server that communicates with hosts over a TCP/IP Ethernet,
giving system administrators centralized control of many distributed
devices. MOXA is now introducing a Dual-host Redundant Data Acquisition
System (DRDASTM) for Async Server
that provides the industrial automation industry with a highly
reliable redundant data acquisition and monitoring system that
can be used in mission-critical environments.
Redundant solution demanded by mission critical applications
In mission critical industries, such as telecommunications, oil
refining, electric power generation, chemical manufacturing, energy
distribution, and monitoring of reservoirs and dams, overall system
reliability is the most important consideration. In order to maintain
high reliability and prevent disaster and financial loss, the
automation system is required to be fault-tolerant and must able
to quickly recover from system shutdowns during any 24-hour period
of operation.
Powerful DRDAS
The new DRDAS Async Server solution offered by Moxa is designed
to guard against data acquisition failures caused by an unresponsive
host. According to statistics, the most critical factor affecting
system reliability is the host PC itself. Various mechanical components,
such as the fan and hard drive, are easily damaged, leading to
a suspension of the host's operating system. With the help of
DRDAS and the robust MOXA Async Server, dual-host configuration
will dramatically increase the overall reliability of your data
acquisition system.
How does DRDAS work?
The following figures illustrate the two states in which DRDAS
operates. The first figure illustrates Normal Operation, during
which the Primary host can send and receive signals to and from
serial devices attached to Async Server. As illustrated in the
Control Status Swap figure, the Secondary host takes over full
control once the Primary host stops responding.
Dual-host configuration
DRDAS works by allowing dual-hosts, designated Primary and Secondary,
to simultaneously receive serial port data from the same Async
Server. The Primary host can effectively both read and write data
from attached serial devices using TCP/IP socket based software,
and although the secondary host can read data from connected devices,
Async Server blocks signals that the secondary host writes to
the devices.
Alive-check watchdog
DRDAS works in conjunction with user-supplied watchdog hardware
and software that is used to establish a dedicated alive-check
link between the two hosts. The watchdog alerts the secondary
host as soon as the primary host's OS has stopped responding.
Depending on the sophistication of the watchdog system being used,
the alert could be issued from anywhere between a few microseconds
to one or two seconds after the crash occurs.
Secondary host takes over
As soon as the Secondary host learns that the Primary host has
crashed, the Secondary host sends a series of commands to Async
Server that "swap" control-right to the Secondary host. This allows
the Secondary host to take over full data acquisition and monitoring
duties. Once the Primary host is back up and running, it sends
a series of commands that "swap" control-right back to the Primary
host, allowing the Primary host to resume full data acquisition
and monitoring.
Instant and reliable redundant solution
There are different levels of redundant solution available on
the market today, with dramatic differences in cost between successive
levels. Async Server's DRDAS provides an instant and reliable
redundant solution. Thanks to the help of DRDAS, investing in
just one more PC can greatly increase the overall reliability
of your data acquisition system.
Real-time control transfer
One of the key features of a redundant system is the control
transfer time, which is one of the factors determining the complexity
of the overall system. MOXA Async Server's DRDAS provides advanced
software technology that uses commands from the Secondary host
to swap control-right. For Async Server itself, the control transfer
time can be as short as tens of milliseconds.
Dual-way data transmission
Serial data sent from the data acquisition point can be transmitted
to different target hosts at the same time. This is an important
feature that minimizes data loss during control transfer.
You may also utilize this feature to establish a data backup
system or a remote monitoring system across the network.
Recommended Product
Versatile applications
DRDAS for Async Server can be applied to the following fields.
- Telecommunications industry
- Energy control
- Energy distribution and monitoring
- Chemical/oil refining industry
- Other mission critical applications
 PDF
format with ordering info is available for download
(File Size: 176KB)
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