Introduction to Industrial Automation

and (d) the timing diagram of I1.2 and M11.0.

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Basic Programming Principles of PLCs 

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313

program for executing the impulse pulse is shown in Figure 7.44c. In this case, the logic coil 

M11.1 is an auxiliary variable to achieve the required logic, while the corresponding Boolean 

language program is as follows:

A

I1.2

AN M11.1

=

M11.0

A

M11.0

S

M11.1

AN I1.2

R

M11.1

A

M11.0

=

Q0.2

A

I1.2

=

Q0.0

BE

A

I1.2

AN M11.1

=

M11.0

A

M11.0

S

M11.1

AN I1.2

R

M11.1

A

M11.0

=

Q0.2

A

I1.2

=

Q0.0

BE

In order to produce a second impulse pulse, the input I1.2 should be deactivated, in order to reset 

M11.1, and then be reactivated.

Example: In an industrial manufacturing process, there are typically many machines 

(motors), each of which may present one or more operating faults, the appearance of which 

is provided in the automation program, and causes either a simple indication or some other 

action. Figure 7.45a shows a series of pumps that may exist in a pump station, each of which 

may exhibit a fault, such as a thermal overload drop, a flow stop, etc. In the examined case, it 

is desired that for any of the apparent fault triggers, a corresponding indication remains active 

(on) for as long as the fault lasts, while simultaneously triggering a corresponding logic coil 

momentary for one scan cycle. In addition, it is desired that the generated impulse of the logical 

coil corresponding to the fault permanently activates a common siren for all faults. The siren 

will stop by pressing a reset button. In the current example, only the case of two faults is consid-

ered, but the logic is expandable for any number of faults without a loss of generality. The con-

nection of the I/O devices is shown in Fig. 7.45b, where the sensors S

1

 and S

2

 represent the two 

faults. Fault 1 is expressed by closing the contact S

1

, while fault 2 is expressed by opening the 

contact S

2

, as shown in the corresponding time diagrams of Figure 7.46. The required Boolean 

PLC

Inputs

Outputs

S

1

0 V

Syren

+24 V DC

0 V

+24 V DC

Q0.0

I2.0

(a)

(b)

Q0.2

S

2

Reset

h

1

h

2

I2.2

I2.4

Q0.4