Page 240 - Programmable Logic Controllers, Fifth Edition - Mobile version

Ladder logic program
as follows:
MEQ Output L2 The operation of the hardwired circuit can be summarized
MASKED EQUAL PL1
PL1 • When the momentary start pushbutton is pressed
Source N7:5
solenoid A is energized immediately.
Mask N7:6 • Solenoid B is energized 5 s later than solenoid A.
Compare N7:10 • Solenoid C is energized 10 s later than solenoid A.
• Solenoid D is energized 15 s later than solenoid A.
Source N7:5 01010101 0101 1111
Mask N7:6 1 1 1 1 1 1 1 1 1 1 1 1 0000 The hardwired time-delay circuit could be implemented
Compare N7:10 01010101 0101 xxxx using a conventional PLC program and three internal

Figure 10-32 Masked comparison for equal (MEQ) timers. However, the same circuit can be programmed
logic rung. using only one internal timer along with data compare in-
structions. Figure 10-34 shows the program required to
implement the circuit using only one internal timer. The
• The mask must be the same element size (16 bits) as
the source and compare addresses. operation of the program can be summarized as follows:
• You must set mask bits to 1 to compare data. Bits • The momentary stop button is closed.
in the compare address that correspond to 0s in the • When the momentary start button is pressed,
mask are not compared. SOL A output energizes immediately to switch
• If you want the ladder program to change mask on solenoid A.
value, store the mask at a data address. Otherwise, • SOL A examine-on contact becomes true to seal in
enter a hexadecimal value for a constant mask value. output SOL A and to start on-delay timer T4:1 timing.
• The timer preset time is set to 15 seconds.
10.4 Data Manipulation Programs • Output SOL B will energize after a total time delay

Data manipulation instructions give new dimension and of 5 seconds, when the accumulated time becomes
flexibility to the programming of control circuits. For ex- equal to and then greater than 5 seconds. This, in
ample, consider the hardwired relay-operated, time-delay turn, will energize solenoid B.
circuit in Figure 10-33. This circuit uses three electrome- • Output SOL C will energize after a total time delay
chanical time-delay relays to control four solenoid valves. of 10 seconds, when the accumulated time becomes
equal to and then greater than 10 seconds. This, in
turn, will energize solenoid C.
L1 L2
• Output SOL D will energize (through the timer done
CR bit T4:1/DN) after a total time delay of 15 seconds
Start
Stop to energize solenoid D.
SOL A
Figure 10-35 shows an application of an on-delay timer
program implemented using the EQU instruction. The op-
1TD
CR eration of the program can be summarized as follows:
1TD SOL B • When the switch (S1) is closed, timer T4:1 will
(5 s)
begin timing.
2TD • Both EQU instructions’ source As are addressed to
get the accumulated value from the timer while it is
2TD SOL C
(5 s) running.
• The EQU instruction of rung 2 has the value of 5
3TD
stored in source B.
3TD SOL D • When the accumulated value of the timer reaches 5,
(5 s) the EQU instruction of rung 2 will become logic
true for 1 second.

Figure 10-33 Three electromechanical time-delay relays • As a result, the latch output will energize to switch
used to control four solenoid valves. the pilot light PL1 on.

Data Manipulation Instructions Chapter 10 221

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