Ladder program elements to deal with active high and/or active low input devices This presentation...

Ladder program elements to deal with active high and/or active low input devices

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Integrating the field devices with a programmable controller and then creating the program that operates the field devices is a critical task.

“We-build-them”

Programmable Controllers

I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts

Simple Programmable Controller that has two input modules and two output modules

Note the different voltage rating for the modules. Other modules with different voltage rating are available.

Input Modules Output Modules

Motor

Starter

To FCE motor

120 volts

N.O.

Simple Programmable Controller that has two input modules and two output modules

Note the different voltage rating for the modules. Other modules with different voltage rating are available.

Input devices

Output device

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts


N.O.

Input devices

If this were a Temperature Sense High alarm device would it have an active high or active low output?

The challenge is not in attaching the wires to an assigned address (terminal) at the appropriate module.

24 volts

N.O.

TSH

(active low)

The important thing is to know if the devices are wired to be active high or active low so you can pick the proper programming element for your ladder program.

N.O.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts


Motor

Starter

To FCE motor

120 volts

Output device


120 volts

What about this Start push button?

N.O.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts


If this were a Temperature Sense High alarm device would it have an active high or active low output?

24 volts

N.O.

TSH

(active low)

Motor

Starter

To FCE motor

120 volts

Output device


120 volts

N.O.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts


24 volts

N.O.

TSH

(active low)

(active low)

Motor

Starter

To FCE motor

120 volts

Output device

Start P.B.


Motor

Starter

To FCE motor

120 volts

Output device

120 volts

N.O.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts


24 volts

N.O.

TSH

(active low)

(active low)

Start P.B.

Now lets attach the output device

Ladder Program

O-0,1

O-0,1I-0,0I-1,3

TSHStart P.B.

Motor

Starter

To FCE motor

120 volts

Output device

120 volts

N.O.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts


24 volts

N.O.

TSH

(active low)

(active low)

Start P.B.

Rule of Thumb for programmable logic controllers“When the computer inside a programmable logic controller senses that an input address is at “logic 1” the computer changes the symbol you put into your program and then executes the ladder program rung.”

Next, we write a ladder program to control this motor.

Ladder Program

Motor

Starter

To FCE motor

120 volts

Output device

120 volts

N.O.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts


24 volts

N.O.

TSH

(active low)

(active low)

Start P.B.

“When the computer inside a programmable logic controller senses that an input address is at “logic 1” the computer changes the symbol you put into your program and then executes the ladder program rung.”

If the input device attached at input address I-0,0 is passive,

(a) Will the programmable control change the symbol that is associated with input address I-0,0 ?

YES !

O-0,1

O-0,1I-0,0I-1,3

TSHStart P.B.

Ladder Program

Motor

Starter

To FCE motor

120 volts

Output device

120 volts

N.O.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts


24 volts

N.O.

TSH

(active low)

(active low)

Start P.B.

“When the computer inside a programmable logic controller senses that an input address is at “logic 1” the computer changes the symbol you put into your program and then executes the ladder program rung.”

If the input device attached at input address I-1,3 is passive,

(a) Will the programmable control change the symbol that is associated with input address I-1,3 ?

YES !

O-0,1

O-0,1I-0,0I-1,3

TSHStart P.B.

“We-build-them” Programmable Controllers

I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts 120 volts

120 volts

48 volts

24 volts

TSH

N.O.

motor

Starter

To motor and FCE

120 volts

120 volts

N.O.

(active high)

(active low)

Notice how this wiring of the temperature alarm input device is different than the previous example.

Start P.B.

“We-build-them” Programmable Controllers

I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts 120 volts

120 volts

48 volts

TSH

N.O.

motor

Starter

To motor and FCE

120 volts

120 volts

N.O.

(active high)

(active low)

Notice how the program symbol for the TSH is also different as well.

Program for previous active low wired temperature sense high alarm device.

Start P.B.

OldNew

You put this symbol into your program so the computer can change it to the other symbol when the terminal I-0,0 changes from logic “0” to logic “1”.

O-0,1

O-0,1I-0,0I-1,3

TSHStart P.B.

O-0,1

O-0,1I-0,0I-1,3

TSHStart P.B.

24 volts

TSH

“We-build-them”


O-0,3

WBT-4

I-1,3 O-1,3

120 volts 120 volts

48 volts

motorStarter

To motor and FCE

I-0,3

24 volts

24 volts

TSH

N.O.

120 volts

N.O.

(active high)

(active low)

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts 120 volts

120 volts

48 volts

motor

Starter

To motor and FCE

Start P.B.

24 volts

TSHN.O.

120 volts

N.O.

(active low)

(active low)

Notice how the wiring of the TSH input devices are different.

Notice how the program elements are different as well. Start

P.B.

O-0,1

O-0,1I-0,0I-1,3

TSHStart P.B.

O-0,1

O-0,1

Ladder Program

I-0,0I-1,3

TSHStart P.B.

O-0,1

O-0,1

Ladder Program

I-0,0I-1,3

TSHStart P.B.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts

motor

Starter

To motor and FCE

120 volts

24 volts

TSH

N.O.

120 volts

N.C.

(active high)

(active high)

Study this example and write the program before you go on.

Start P.B.

Ladder Program

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts

motor

Starter

To motor and FCE

120 volts

TSH

N.O.

(active high)

Now try this one.

24 volts

120 volts

N.C.

(active low)

Start P.B.

O-0,1

O-0,1I-0,0I-1,3

TSHStart P.B.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

motorStarter

To motor and FCE

24 volts

TSH

N.O.

120 volts

Start P.B.

N.C.

(active high)

(active low)

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

motorStarter

To motor and FCE

24 volts

TSH

N.O.

120 volts

Start P.B.

N.C.

(active high)

(active high)

Notice the difference.

O-0,1

O-0,1

Ladder Program

I-0,0I-1,3

TSHStart P.B.

Notice the difference.

24 volts

TSH

N.O.

120 volts

Start P.B.

N.C.

(active high)

(active high)

24 volts

TSH

N.O.

120 volts

Start P.B.

N.C.

(active high)

(active low)O-0,1

O-0,1

Ladder Program

I-0,0I-1,3

TSHStart P.B.

“We-build-them”


I-0,3 O-0,3

WBT-4

I-1,3 O-1,3

24 volts

120 volts

120 volts

48 volts

24 volts

TSH

N.C.

motor

Starter

To motor and FCE

120 volts

120 volts

Start P.B.

N.C.

O-0,1

O-0,1

Ladder Program

I-0,0I-1,3

TSHStart P.B.

(active high)

(active Low)

Self assessment tool

Write the program for this input device configuration.

Check your answer, if it doesn’t agree run this presentation again.

Ladder program elements to deal with active high and/or active low input devices This presentation...

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