Page 376 - Programmable Logic Controllers, Fifth Edition - Mobile version

Solenoid A Full tank
L1 sensor L2
Fill
Stop
1CR
1CR
Full tank 1
sensor
1CR 2 Solenoid A

Empty tank
sensor Empty tank
Empty sensor
Control panel 2CR
Stop Solenoid B 2CR 1
Fill
Empty
2CR 2 Solenoid B

Figure 15-48 Hardwired tank filling and emptying operation for Problem 4.

The operation of the control circuit can be summa- • Anytime the liquid level of the tank is above
rized as follows: the empty-level mark, momentarily pressing
• Assuming the liquid level of the tank is at or below the EMPTY pushbutton will energize control
the empty level mark, momentarily pressing the relay 2CR.
FILL pushbutton will energize control relay 1CR. • Contacts 2CR and 2CR will both close to seal
1
2
• Contacts 1CR and 1CR will both close to seal in the 2CR coil and energize normally closed
1
2
in the 1CR coil and energize normally closed solenoid valve B to start emptying the tank.
solenoid valve A to start filling the tank. • When the liquid reaches the empty level, the
• As the tank fills, the normally open empty-level normally open empty-level sensor switch opens
sensor switch closes. to open the circuit to the 2CR relay coil and
• When the liquid reaches the full level, the normally switch solenoid valve B to its de-energized
closed full-level sensor switch opens to open the closed state.
circuit to the 1CR relay coil and switch solenoid • The stop button may be pressed at any time to halt
valve A to its de-energized closed state. the process.

Bit-Level Programming Part 2 357

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