Programming the Controller Application in the Project

Select the Application entry and click Add Object → Global Variable List in the context menu. Change the default name GVL to Glob_Var and click Add to confirm.

When the textual view opens, it already contains the keywords VAR_GLOBAL and END_VAR. For our example, click the button on the right sidebar of the editor to activate the tabular view.

In the context menu, click Insert.

Specify rTempActual in the Name field.

Double-click in the field of the Data Type column.

Click the button and then select Input Assistant.

Select the data type REAL and click OK.

Enter a numerical value in the Initialization column (example: 8.0).

In the device tree, double-click PLC_PRG.

In the ToolBox view, select the Input element and drag it to the CFC editor below the PLC_PRG tab.

In the CFC editor, click ??? at the input, and then click to open the Input Assistant. In the Variables category, select the rTempActual variable below Application → Glob_Var. This is how to reference the global variable rTempActual here.

As in Step 3, create another input with the name of the global variable Glob_Var.rTempSet.

Create another input, and then click ??? and replace them with the name rHysteresis.

In the Auto Declare dialog, specify the Type as REAL and Initialization as 1. Click the OK button.

In the ToolBox view, select Block element and drag it to the CFC editor below the PLC_PRG tab.

Replace ??? with ADD.

Connect the Glob_Var.rTempSet input to the ADD POU. To do this, click the output pin of the input and drag it to the upper input pin of the ADD POU.

In the same way, connect the input rHysteresis with the lower input of the ADD POU.

To move an element in the editor, click an empty space in the element or click the frame, so that the element is selected (red border, red highlight). Drag the element to the desired position.

Create another POU to the right of the ADD POU. Its purpose is to compare Glob_Var.rTempActual with the sum of Glob_Var.rTempSet and rHysteresis. Assign the GT function (greater than) to the POU.

Connect the input Glob_Var.rTempActual to the upper input of the GT POU.

Connect the output of the ADD POU to the lower input of the GT POU.

Now use the block element to create a function block to the right of the GT POU which starts and stops the compressor depending on the input conditions (Set – Reset). Specify the name SR in the ??? field. Press the Enter key to close the open input field above the POU (SR_0).

Declare the variable with the name SR_0 and the data type SR. Click the OK button.

Connect the output pin on the right of the GT POU to the SET1 input of the SR_0 POU.

Create an Output element and assign it to the global variable Glob_Var.xCompressor. Drag a connecting line between Glob_Var.xCompressor and the output pin Q1 of SR.

In the device tree, right-click the Application object and add a POU object of type Program with the Ladder (LD2) implementation language.

Name the program as Signals.

Create a program in the network so that an audible signal sounds when the compressor runs too long without reaching the specified temperature. To do this, insert a TON timer POU in the next steps. It switches a Boolean signal to TRUE after a specified time.

In the ToolBox view, drag the Block element and drop it into the empty network to an available insertion position.

Double-click the three question marks (???) in the block and click the symbol in the line editor.

In the Input Assistant dialog, in the Standard function blocks category, in the Standard library, select the TON Timer and click OK.

Now in the line editor of the block, which shows the function block name TON, press the Enter key.

To remove the EN input and the ENO output, select the block and click the EN/ENO → EN in the context menu.

Double-click the three question marks [???] directly above the block, specify TON_0 as the instance name, and press the Enter key.

Click OK to confirm the dialog.

Program the block to be activated as soon as the compressor starts running. First drag the Contact ladder element from the ToolBox view in front of the IN input of the block. Double-click the three question marks and click the icon in the line editor (). In the Input Assistant, now select the already declared global variable xCompressor and click OK.

Insert the signal that is to be activated. To do this, drag a Coil from the ToolBox view, Ladder category, to the Q output of the TON block. Specify the name Glob_Var.xSignal for the coil.

Define the time period from the activation of the POU TON_0 until the signal should sound. This definition takes place via the variable Glob_Var.timAlarmThreshold, which you insert for this purpose at the input PT of TON_0. To do this, move the mouse pointer to the left end of the input pin of input PT. Click the fine-edged box which is now displayed to left of the input pin and specify the variable name.

Press the Enter key.

Click OK to confirm the dialog.

Right-click the TON POU and click Remove unused pins in the context menu.

In the second network of the LD, program so that the signal sounds intermittently when the door is open too long.

Use the mouse to drag an Network element from the ToolBox view to the insertion point below Network 1.

As in the first network, implement a TON POU for time-controlled activation of the signal. This time it is triggered by the global variable Glob_Var.xDoorOpen at the input IN. At the input PT, add the global variable Glob_Var.timDoorOpenThreshold.

From the Util library, add a BLINK POU at the output Q of the TON POU in this network and instantiate it with the name Blink_0.

The BLINK_0 POU clocks the signal forwarding Q and therefore Glob_Var.xSignal.

First, drag two Contact elements from the ToolBox view to the OUT output of the POU. Assign the variable TON_1.Q to the contact directly after the output Q and the global variable Glob_Var.xDoorOpen to the second contact.

Insert a Coil element after the two contacts and assign the global variable Glob_Var.xSignal to it.

Declare the local variable timSignalTime : TIME := T#1S; and insert this variable at the inputs TIMELOW and TIMEHIGH. The cycle time is 1 second for TRUE and 1 second for FALSE.

Right-click the TON POU and click Remove unused pins in the context menu.

In the third network, program so that the lamp lights up as long as the door is open. Add an additional network and a contact. Assign the variable GlobVar.xDoorOpen to the contact.

The inserted contact leads directly to a coil. Add a coil to the right of the contact and assign the global variable Glob_Var.xLamp to the coil.

CODESYS processes the networks of an LD one after the other. Now install a jump to Network 3 at the end of Network 1 in order to ensure that either only Network 1 or only Network 2 is executed:

When you hover the mouse pointer over the 3rd line in the top left-hand edge of the network, the information <insert jump here> is displayed. Double-click this position and specify DoorIsOpen: as the jump label in the line editor.

Select the Network 1. From the ToolBox view, Ladder Diagram category, drag the Jump element to the insertion position marked with a triangle in front of the Glob_Var.xSignal coil.

Double-click the three question marks [???] and click the symbol in the line editor. In the Input Assistant dialog, select DoorIsOpen from the possible label identifiers and click OK to confirm.

In the device tree, double-click PLC_PRG.

In the Toolbox view, drag a Block element to the editor of PLC_PRG.

Double-click the three question marks [???] and click the symbol in the line editor. In the Input Assistant dialog, in the POU / Program and Function Calls category, select the Signals program and click OK to confirm.

In the device tree, right-click the Application object and add a POU object of type Program with the Structured Text (ST) implementation language. Name the POU as Simulation.

Implement the following code in the ST editor:

Declaration part:

PROGRAM Simulation
VAR
        TON_1: TON;                         //The temperature is decreased on a time delay, when the comepressor has been activated
        P_Cooling: TIME:=T#500MS;
        xReduceTemp: BOOL;                  //Signal for dereasing the temperature
        TON_2: TON;                         //The temperature is increased on a time delay
        P_Environment: TIME:=T#2S;          //Delay time when the door is closed
        P_EnvironmentDoorOpen: TIME:=T#1S;  //Delay time when the door is open
        xRaiseTemp: BOOL;                   //Signal for increasing the temperature
        timTemp: TIME;                      //Delay time
        iCounter: INT;
END_VAR

Implementation part:

iCounter := iCounter + 1;     // No function, just for demonstration purposes.

// After the compressor has been activated due to TempActual being too high, the temperature decreases.
// The temperature is decremented by 0.1°C per cycle after a delay of P_Cooling
IF Glob_VAR.xCompressor THEN
        TON_1(IN:= Glob_Var.xCompressor, PT:= P_Cooling, Q=>xReduceTemp);
        IF xReduceTemp THEN
                Glob_Var.rTempActual := Glob_Var.rTempActual-0.1;
                TON_1(IN:=FALSE);
        END_IF
END_IF

//If the door is open, the warming occurs faster; SEL selects P_EnvironmentDoorOpen
timTemp:=SEL(Glob_Var.xDoorOpen, P_Environment, P_EnvironmentDoorOpen);

//If the compressor is not in operation, then the cooling chamber becomes warmer.
//The  temperature is incremented by 0.1°C per cycle after a delay of tTemp
TON_2(IN:= TRUE, PT:= timTemp, Q=>xRaiseTemp);
IF xRaiseTemp THEN
        Glob_Var.rTempActual := Glob_Var.rTempActual + 0.1;
        TON_2(IN:=FALSE);
END_IF

In the device tree, drag the Simulation entry to MainTask below the Task Configuration.

To view the task configuration, double-click the MainTask entry to open the editor.