Page 142 - Programmable Logic Controllers, Fifth Edition - Mobile version

L1 Ladder logic program Internal L2
PB1 PB2 LS relay
Input module Output module
wiring connections I:3/0 I:3/1 I:3/2 B3:1/0 wiring connection

B3:1/0 OL
PB1
O:4/1 M
I:3/0 PL1
B3:1/0 O:4/2
PB2
PL1
I:3/1
PL2 O:4/2 R
LS B3:1/0 O:4/3
I:3/2
PL2
M O:4/3 G
B3:1/0 O:4/1

Figure 6-65 Sequential process PLC ladder logic program.

Instruction most Instruction least A H1 H3 H2 H4 B
likely to be FALSE likely to be FALSE

120 V
X1 X2
Start
Figure 6-66 Series instructions programmed for optimum Stop OL
scan time. CR

Jog CR1
placed on the top of the rung. The processor will not look
at the others unless the top path is false. M
Figure 6-68 shows a hardwired jog control circuit that CR2 M
incorporates a jog control relay. The operation of the cir-
cuit can be summarized as follows:

• Pressing the start pushbutton completes a circuit for
the CR coil, closing the CR1 and CR2 contacts. Control relay
• The CR1 contact completes the circuit for the M Figure 6-68 Jog circuit with control relay.
coil, starting the motor. Source: Photo courtesy IDEC Corporation, www.IDEC.com/usa, RR Relay.

Path most likely to be TRUE • The M maintaining contact closes; this maintains
the circuit for the M coil.
• Pressing the jog button energizes the M coil only,
starting the motor. Both CR contacts remain open,
Less likely
and the CR coil is de-energized. The M coil will
not remain energized when the jog push button is
released.
Least likely
Figure 6-69 shows a PLC program equivalent of the
hardwired relay jog circuit. Note that the function of the
Figure 6-67 Parallel instructions programmed for control relay is now accomplished using an internal PLC
optimum scan time. instruction (B3:1/0).

Developing Fundamental PLC Wiring Diagrams and Ladder Logic Programs Chapter 6 123

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