Emerson Tescom ER5000 Series, Руководство пользователя, Страница: 43 / 248

ER5000 —
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Control Modes
The ER5000: Control Modes
Internal Feedback Mode
Internal Feedback Mode uses the ER5000’s internal
sensor to monitor the pressure within the controller’s 0–100 psig /
0–6.9 bar internal pressure range. This mode is typically used
when the ER5000 is used as a standalone unit or when open-loop
control of a regulator is desired.
External Feedback Mode
External Feedback Mode uses a user-supplied external transducer
to monitor the system pressure. The transducer is installed in the
process line and provides direct feedback to the ER5000. This mode
is typically used when the ER5000 acts as the pilot regulator for a
regulator or valve.
An external transducer may also be installed in the ER5000’s
pressure line when the ER5000 is used as a standalone unit. This
may be preferable to Internal Feedback mode when:
• The application requires precise control within a small pressure
range. For example, the ER5000 will respond more efficiently
to a 5% change in a 0–10 psig / 0–0.7 bar range than to a 0.5%
change in its full 0–100 psig / 0–6.9 bar range.
• There is a need to monitor downstream pressure. For example,
if the output passes through a length of pipe to a vessel and it is
expected that there will be pressure drops in the pipe, an external
sensor installed at the vessel will provide a more responsive
feedback signal than the controller’s internal sensor.
Cascade Mode
Cascade Mode implements one PID loop within another PID loop.
The inner loop uses the controller’s internal sensor and the outer
loop uses an external sensor. This mode of operation creates more
stability, but slows down the response of the system.
NOTE NOTE
CAUTION CAUTION
WARNING WARNING
For proper operation in Cascade Mode, the following
recommended defaults for the Integral Limits of the external feedback
loop (also known as the outer loop) are downloaded into the controller
during setup: Maximum: 32767; Minimum: 0. These settings are optimal
for most applications.
Refer to The Cascade Tuning Tips and The Integral Limits
Controllers for more information on these settings.