B-320-2-E
4
5.3 Operation Time Chart and Pneumatic Circuit
■
Description of Operation Time Chart
NOTE: Operation can best be understood by referring to the chart below.
Upon depression of
START
▲
. button, the shutoff valve opens to a predetermined position (initial flowrate). When a
predetermined quantity (from point A to point B) has been delivered, the valve opens fully; when metering has
reached point C, the valve automatically throttles the flow and maintains a predetermined valve position (final
flowrate).
At point D (batch setpoint), a closure signal (full closure signal) is generated.
However, due to a time lag in valve actuation, inherent to the type of valve used, the valve actually closes at
point E. Since the amount from point D to point E can be anticipated (an overshoot or over measurement),
we determine the right batch setpoint corrected for this overshoot. If an overshoot exceeds a predetermined
quantity, the register sets off an alarm.
Safe and precise measurement is thus achieved. In practice, we preselect valve positions A
→
B and C
→
D on
the part of the shutoff valve.
NOTE: In a model equipped with LW76E register, manual interruption while the valve is fully open causes
the shutoff valve to close in one step and, when operation is resumed for the remaining batch
process, it opens up in one step.
<Operation Time Chart>
INITIAL FLOW CONTROL
(INITIAL SETTING)
OUT 2
(SV)
OUT 1
(MV)
ON
OFF
ON
OFF
START SIGNAL
VALVE POSITION
(FLOWRATE)
INITIAL FLOWRATE
A
B
C
D
E
TIME
ANTICIPATED
OVERSHOOT
END OF A BATCH
FINAL FLOWATE
UPPER LIMIT FLOWRATE
STOP SIGNAL
FULL OPEN SIGNAL
ONE-STEP OPEN SIGNAL
TARGET BATCH SET VALUE
FINAL FLOW CONTROL
(FINAL SETTING)
NOTE: Shown in this chart is the 2-step open, 2-step close arrangement. In
the one-step open or one-step close mode, set both the initial and
final setting to 0.
Fig. 5.3
