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FIGURE 9.2 Dual-level control. Communications 441
and OFF when the maximum level has been reached:
Max = 1
Min = 1
If the level is between the two levels
Max = 0
Min = 1
the motor maintains the current status.
The constant level is disturbed by varying the bleed-off valve.
These requirements are shown in a fact table, where P represents a cur-
rent status and PN represents the required pump status (Table 9.1).
Max Min P Port PN
0 0 0 I 1
0 0 1 I 1
0 1 0 I 0
0 1 1 I 1
1 1 0 I 0
1 1 1 I 0
TABLE 9.1 Fact Table
