Emerson Rosemount, Справочное руководство

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45
Reference Manual
00809-0100-4021, Rev GC
Section 3: HART commissioning
April 2014
HART® commissioning
Hot Backup feature configuration
Field communicator
The Config Hot BU command configures the transmitter to automatically use Sensor 2 as the
primary sensor if Sensor 1 fails. With the Hot Backup feature enabled, the primary variable (PV)
must either be First Good or Sensor Average. See
“Average temperature” on page 43 for details
on using the Hot Backup feature when PV is Sensor Average. Sensors 1 or 2 can be mapped as
the secondary variable (SV), tertiary variable (TV), or quaternary variable (QV). In the event of a
primary variable (Sensor 1) failure, the transmitter enters the Hot Backup feature mode and
Sensor 2 becomes the PV. The 4–20 mA signal is not disrupted, and a status is available to the
control system through HART that Sensor 1 has failed. An LCD display, if attached, displays the
failed sensor status.
While configured to the Hot Backup feature, if Sensor 2 fails but Sensor 1 is still operating
properly, the transmitter continues to report the PV 4–20 mA analog output signal, while a
status is available to the control system through HART that Sensor 2 has failed. In the Hot
Backup feature mode, the transmitter will not revert back to Sensor 1 to control the 4–20 mA
analog output, until the Hot Backup feature mode is reset by either re-enabling through HART
or by briefly powering down the transmitter.
For information on using the Hot Backup feature in conjunction with the HART Tri-Loop
™
see
“Use with the HART Tri-Loop” on page 99 .
Problem description: The unexpected failure of a critical temperature measurement can cause
safety issues, environmental or regulatory concerns, and process shutdowns.
Our solution: The Hot Backup feature allows the transmitter to automatically switch the
transmitter input from the primary sensor to the secondary sensor should the primary sensor
fail. This prevents a process disruption due to the failure of the primary sensor. A maintenance
alert is also generated to notify operators that a sensor has failed and the Hot Backup feature is
active.
How it works: Two sensors are wired to a dual-input transmitter. The 2 sensors are measured in
alternating fashion, so when sensor 1 failure is detected, the transmitter can immediately
switch the output to reflect the sensor 2 value. The switch is automatic with no disruption to the
analog output. The transmitter sends a digital alert to inform the users that the Hot Backup
feature is active and the primary sensor needs investigation.
Take away: “The Hot Backup feature prevents primary sensor failure from disrupting process
control.”
Target applications: Redundant measurements, critical measurements, trouble spots.
HART 5 Fast Keys
2, 2, 4, 1, 3
HART 7 Fast Keys
2, 2, 4, 1, 3