Page 28 - Programmable Logic Controllers, Fifth Edition - Mobile version

Input Output
module module L1 N
120 VAC
Pressure
L1
0 0 OL

Temperature 1 1 M
2 2 Motor
3 3 starter coil
4 4
5 5
Manual 6
pushbutton 6
7 7

L1 N Figure 1-19 Typical wiring connections for a 120 VAC
120 VAC Common
modular configured output module.
Source: Photo courtesy Automation Direct, www.automationdirect.com.
Figure 1-18 Typical wiring connections for a 120 VAC
modular configured input module.
Source: Photo courtesy Automation Direct, www.automationdirect.com. The same output field device (motor starter coil) would
also be used. This device would be hardwired to an appro-
Now let’s look at how a programmable logic controller priate output module according to the manufacturer’s ad-
might be used for this application. The same input field dressing location scheme. Typical wiring connections for
devices (pressure switch, temperature switch, and push- a 120 VAC modular configured output module are shown
button) are used. These devices would be hardwired to in Figure 1-19.
an appropriate input module according to the manufac- Next, the PLC ladder logic program would be con-
turer’s addressing location scheme. Typical wiring con- structed and entered into the memory of the CPU. A
nections for a 120 VAC modular configured input module typical ladder logic program for this process is shown in
are shown in Figure 1-18. Figure 1-20. The format used is similar to the layout of

Inputs Program Output
Motor
L1 Pressure Temperature starter L2
I/1 switch switch coil
I/1 I/2 O/1 OL
O/1 M
I/2 Manual
pushbutton
I/3

I/3

Monitor ... Checks the
inputs inputs

Execute ... Executes control
program program

Change ... And updates the
outputs outputs

Figure 1-20 Process control PLC ladder logic program with typical addressing scheme.

Programmable Logic Controllers (PLCs) Chapter 1 9

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