
3Ć54 Theory of Operation: Redundancy
Original Ć June 1990CE4.2:CL6211
Functionally, this form of redundancy is often referred to as hot backup"
or hot spares", because the extra unit is standing in a configured and
powered up state, prepared to resume the control actions as quickly as
possible whenever a fault should happen to occur.
3.6.2 Redundant Controller Upload and Download
3.6.2.1 Upload and Download Transparency
The user downloads a redundant controller using the same method as
downloading any simplex (non-redundant) controller.
3.6.2.2 Initialization of Control Action After Download
Initialization of the control algorithms after a download proceeds as
follows:
1. Download data is received at the ACTIVE unit. During the duration of the
download, the ACTIVE controller is performing an output hold operation on
all analog output channels.
2. At the completion of a download the ACTIVE controller resumes its normal
control algorithms. See the section on Upload/Download for a more
detailed explanation of initialization of the output channels after a download.
3. Immediately after the completed download, the configuration is passed to
the STANDBY controller over the inter-controller communications link.
This communications link is established via the interconnects in the
controller card file.
4. Once the STANDBY controller has successfully received the complete
download data transfer, normal inter-controller tracking operations are
performed.
3.6.2.3 Recovery After Configuration Download Error Detection
If a configuration error is detected during the download of a redundant
controller, or if a timeout occurs during the download sequence because
the download transmission is unsuccessful for some reason, the ACTIVE
redundant controller will abort the download in progress, and reload the
previous configuration from Non-Volatile Memory (NVM). If at the same
time the redundant controller is reporting an NVM error, it will remain in
database hold until a download is successful.
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