Micromod Micro-DCI: 53SL6000 Single Loop Controller - Manual (Page 90)

8.2 Analog Back-Up Control
The direct digital control/analog back-up strategy
is used in operations where a remote computer is
normally controlling the final element directly. It is
implemented with the controller default settings,
the SnGL control scheme, and the path connec-
tions provided on the next page in Section 8.2.8.
A control/analog back-up strategy is illustrated in
Figure 8-3.
With this control strategy, the controller functions
as a signal selector and automatic back-up unit to
the computer host. The controller assumes proc-
ess control in the event of a signaled computer
failure. The analog back-up controller operates as
a single loop controller when driving the process
final element (e.g., output valve).
While in back-up and automatic, the controller con-
tinually adjusts its output to match the AI2 control
element feedback signal so that transfer to online
operation is bumpless in the event of computer
failure. Selection of the computer or back-up con-
troller signals to the process final element is per-
formed by the controller’s DO1 and DO2 modules
in conjunction with blocking diodes (see circuit dia-
gram in Figure 8-4). The computer drives the final
process element when remote operation is se-
lected with the controller R/L push button and digi-
tal input DI1 is closed (0-1 V dc); otherwise, the
computer’s control signal is diverted and the output
from the controller is the active signal to the proc-
ess final element. Unless DI2 input is open (4-24 V
dc signal), the controller is not permitted to operate
in automatic mode.
The signal connector is illustrated in Figure 8-5 and
the connector pin assignment descriptions are pro-
vided in the sections that follow. These sections
also contain the applicable display prompts that
may require configuration changes.
Figure 8-3. Backup Control Application
Figure 8-4. Output Selector
Figure 8-5. Backup Control Signals
Section 8. Eight Control Strategies 53SL6000 Instruction Manual
8-3