Solenoid B Full tank sensor Solenoid A Empty tank sensor Control panel Stop Fill Empty Figure 15-48 Hardwired tank filling and emptying operation for Problem 4. The operation of the control circuit can be summarized as follows: • Assuming the liquid level of the tank is at or below the empty level mark, momentarily pressing the FILL pushbutton will energize control relay 1CR. • Contacts 1CR1 and 1CR2 will both close to seal in the 1CR coil and energize normally closed solenoid valve A to start filling the tank. • As the tank fills, the normally open empty-level sensor switch closes. • When the liquid reaches the full level, the normally closed full-level sensor switch opens to open the circuit to the 1CR relay coil and switch solenoid valve A to its de-energized closed state. L1 L2 Stop Fill 1CR1 Empty 2CR1 1CR2 Solenoid A Empty tank sensor 2CR2 Full tank sensor 1CR 2CR Solenoid B • Anytime the liquid level of the tank is above the empty-level mark, momentarily pressing the EMPTY pushbutton will energize control relay 2CR. • Contacts 2CR1 and 2CR2 will both close to seal in the 2CR coil and energize normally closed solenoid valve B to start emptying the tank. • When the liquid reaches the empty level, the normally open empty-level sensor switch opens to open the circuit to the 2CR relay coil and switch solenoid valve B to its de-energized closed state. • The stop button may be pressed at any time to halt the process. Bit-Level Programming Part 2 357
Petruzella_ProgrammableLogicControllers__5e
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