Experiment 7: Perform Temperature and water level control using PLC.

Hardware:

There are three hardware unit in this PLC. A main PLC unit, one for water level control and other for temperature control. The main unit has different input output elements and ports, like latch switches, push button switches, LED indicator, anneunciator, volt meter, ammeter, relays, ADC channels, DAC channels etc. At the back side of the main unit there are three com ports to connect the additional units, like water level control unit, temperature control unit, lift control unit, with the main unit.

Software:

The software used for this PLC is “PLC Trainer Ver 9.1” developed by Kuruganti Computers Pvt. Ltd. This software has two screen or panel. One is programming panel and the other one is display panel. When the software is opened, the programming panel first open and from the programming panel we can navigate to display panel by pressing F5. And we can return back to programming panel from display panel by pressing Ctrl+L .

Programming Panel:

In the programming panel there are many instruction icons present and where we can actually design our ladder diagram. The fig. shows the screen shot of programming panel.

Each and every instruction when used in the program it should be confirmed by clicking over the Confirm Button. Let’s know about some instruction icons.

  

Rung Instructions:

Start Rung:

This instruction signifies the beginning of a rung or line in a ladder diagram. All rungs in a program should begin with this instruction. The Start Rung instruction stores the rung number of a rung. The rung numbers do not determine the the sequence of execution of rungs in a program. In the event of an error, the rungs are addressed by their rung numbers.

End Rung:

This instruction signifies the end of a rung. This instruction should be used only at the end of a rung. All rung should end with this instruction. This instruction is the equivalent of a semicolon (;) in a high level language like ‘C'.

Input Instructions:

When High:

This instruction is a condition pertaining to Digital Inputs. The condition is satisfied only when the input status of a digital input is at a logic high state.

When Low:

This instruction is a condition pertaining to Digital Inputs. The condition is satisfied only when the input status of a digital input is at a logic low state.

On High:

This instruction is a condition pertaining to Digital Inputs. The condition is satisfied only when the input status of a digital input changes from a logic low state to a logic high state.

On Low:

This instruction is a condition pertaining to Digital Inputs. The condition is satisfied only when the input status of a digital input changes from a logic high state to a logic low state.

Output Instructions:

Set Output:

This instruction is used to set a digital output to a logic high state. This is executed conditionally, means it is executed only if the conditions preceding it are satisfied.

Reset Output:

This instruction is used to set a digital output to a logic low state. This is executed conditionally, means it is executed only if the conditions preceding it are satisfied.

Latch Output:

This instruction is similar to set output instruction. The only difference is that there is no else statement in the equivalent. This means that once the digital output is set, it stays set, unless another Unlatch Output instruction is used to reset the output.

Unlatch Output:

This instruction is similar to Reset Output instruction. The only difference is that there is no else statement in the equivalent. This means that once the digital output is set, it stays set, unless another Latch Output instruction is used to set the output.

When Output High:

This instruction is a condition pertaining to digital outputs. The condition is satisfied only when the output status of a digital output is state at high state.

When Output Low:

This instruction is a condition pertaining to digital outputs. The condition is satisfied only when the output status of a digital output is state at high state.

Flag Instructions:

Set Flag:

This instruction is same as the Set Output Instruction. The difference is that when this instruction is used a flag is set instead of a digital output.

Reset Flag:

This instruction is same as the Reset Output Instruction. The difference is that when this instruction is used a flag is reset instead of a digital output.

When Flag High:

This instruction is a condition pertaining to flags. The condition is satisfied only when the status of a flag is at a logic high state.

When Flag Low:

This instruction is a condition pertaining to flags. The condition is satisfied only when the status of a flag is at a logic low state.

Arithmetic Instructions:

Addition:

This instruction is used to add the content of two resisters.

Destination = Operand#1 + Operand#2

Subtraction:

This instruction is used to subtract the content of a resister from the content of another resister.

Destination = Operand#1 – Operand#2.

Multiplication:

This instruction is used to multiply the content of two resister.

Destination = Operand#1 X Operand#2.

Division:

This instruction is used to divide the content of a resister by the content of another resister.

Destination = Operand#1 / Operand#2.

Increment:

This instruction is used to increment the content of a resister by 1.

Operand = operand + 1.

Decrement:

This instruction is used to decrement the content of a resister by 1

Operand = Operand – 1.

Data Transfer Instructions:

Load Data:

This instruction is used to load a value in to a resister. When this instruction is executed the data already stored in the destination is overwritten.

Destination = Value.

Move Data:

This instruction is used to move data from a source to a destination. When this instruction is executed, the data already stored in the destination is overwritten.

Destination = Source.

Compare Instruction:

This instruction is a condition. The condition is satisfied only when the compare condition is satisfied. The compare condition depends on the compare operator. This instruction allows one to compare the content of two resisters. This facility is essential to develop a closed loop feedback parameters like temperature, pressure, flow etc. the list of compare operators is given below:

Sl no	Compare Operator	Explanation
1	>	Greater than
2	> or =	Greater than or equal to
3	=	Equal to
4	Not =	Not equal to
5	< or =	Less than or equal to
6	<	Less than

Timer Instructions:

Start Timer:

This instruction is used to start a timer. When this instruction is executed, the timer starts running. If the timer is already running when this instruction is executed, the timer starts again from the beginning, the previous status of the timer is ignored. One the timer has started running, it is set after preset time is elapsed.

Reset Timer:

This instruction is used to reset a timer. When this instruction is executed the timer is reset, irrespective of its previous status.

When Timer Set:

This instruction is a condition. The condition is satisfied only when the timer is set. This instruction is used to perform any event after a time delay.

Counter Instruction:

Increment Counter:

This instruction is used to increment the count status of a counter. Every time this instruction is executed, the count status of the counter increments by 1, irrespective of the status of the counter. If the count status of the counter is greater than or equal to the preset count value, the counter is set.

Reset Counter:

This instruction is used to reset a counter. When this instruction is executed, the counter is reset, irrespective of its previous state.

When Count Complete:

This instruction is a condition. The condition is satisfied only when the counter is set. This instruction is used to perform any event when the preset count is reached.

Note:

To set timer value press Ctrl+t or go to View à components àtimer components. Then choose the timer and set its value.

To set counter value press Ctrl+u or go to View à components àcounter components. Then choose the counter and set its value.

To set resister value press Ctrl+r or go to View à components à Resister Component. Then choose the resister and set its value.

Display Panel:

The display panel basically shows the status of all input output devices, ADC values, all timer, counter and resister values etc. the fig. shows the screen shot of display panel.

Procedure to start:

Click on the PLC Trainer Ver 9.1 shortcut over the desktop. Switch ON the main PLC unit.

Click on Continue

The programming panel will open.

Drag and drop the Start Rung over the programming area and confirm it by clicking over confirm.

Then drag and drop other required input output instructions and confirm each one.

The save the file. Go to Run tab and click on compile and Run or press F5.

Then the display panel will open where you can test your program, and see the status of input output devices. Then go to view tab and click on ladder program or press Ctrl+l to go back to program panel for editing the program.