1 Brief Ladder Logic Overview - GitHub

BRIEF LADDER LOGIC OVERVIEW 1 1.1 Brief ladder logic Overview Learning Objective Explain ladder logic Create basic circuits in ladder logic Introduce ladder logic tools Use library classes in ladder logic. 18.05.2015 Page 1

BRIEF LADDER LOGIC OVERVIEW 1.2 What is Ladder logic? Ladder logic, also known as a Ladder diagram, is a method for programming for Programmable Logic Controls. Ladder Logic is a standardized type of graphic programming, which is similar to a circuit diagram. Programming with ladder logic is used, in particular, for creating logic controls. 1.2.1 Task: OR Gate Using a ladder diagram, create an OR gate. For this purpose, two inputs and one output are placed. An OR gate is then placed between the two inputs, so that either input 1 OR input 2 must be set in order to enable the output. 1.2.2 Project start Save the project under: C:\SigmatekWorkshop Assign it the project name: LadderExample Go online with the control and load the hardware from the S-DIAS set using the hardware editor. Compile the project (F9) and download it to the PLC. Next, create a Ladder Diagram class. To create this class, right-click on the project name LadderExample in the Class View window. Assign the name ORFunction. In the Properties window, set Cyclic Task to true and assign a Default Cyclic time of 100 ms. Page 2 18.05.2015

BRIEF LADDER LOGIC OVERVIEW By activating the Cyclic task, the other two tasks (Realtime and Background) are disabled automatically. A ladder diagram class can therefore be assigned only one of the three tasks. Create a new network with the name LadderNet and place the ORFunction in it. When creating the ladder class, a network called ORFunction is created. This network is however, not created in the network tree but in the Network folder of the ORFunction class. In is important to note that each instanced object of a ladder class has its own network. Open the network of the object by placing the mouse pointer on the upper right corner of the object and double clicking on the symbol that appears. 18.05.2015 Page 3

BRIEF LADDER LOGIC OVERVIEW As can be seen, the workspace of the network is divided in a grid. Elements can be placed in the individual fields of the grid. With a right-click in the upper left field, the context menu is opened. Place a contact in the network as shown in the following screenshot. In the network field below, place a second input. Change to the LadderNet network. As can be seen, two new clients were added to object. Page 4 18.05.2015

BRIEF LADDER LOGIC OVERVIEW Next, placed a coil in the second column of the ORFunction network. Create a connection between the elements as shown in the following screen shot: Change back to the LadderNet network. As can be seen, not only the inputs (clients Input1 and Input2) were created, but also the output (Output server). For the output, a client with the name Clt Output is also created. This client is used to connect the output to a hardware component. 18.05.2015 Page 5

BRIEF LADDER LOGIC OVERVIEW Create a connection to the hardware with the IO Connection Manager according the following screenshot. If an input is renamed, the client in the class is also renamed. If an output is renamed, the server and client in the class are also renamed. In the client name, the abbreviation "Clt " is retained. Compile the project then go online with the control. Enable the Save Project on PLC checkbox in the Download dialog window and load the project to the control with Download Project & Run. Confirm with the Switch1 button. If the input is active, the set input and output are colored green. Page 6 18.05.2015

BRIEF LADDER LOGIC OVERVIEW In the LadderNet network, how the clients Input and Clt Output (or Switch1 and OutputLed1) as well as the Output server are set to 1 can be seen. If the Switch2 button is pressed, the output is also set (see following graphic): The switching process can also be monitored in the object. 18.05.2015 Page 7

BRIEF LADDER LOGIC OVERVIEW Go offline and delete the connection between Switch1 and Input in the LadderNet network. Compile the project then go online with the control. Enable the Save Project on PLC checkbox in the Download dialog window and load the project to the control with Download Project & Run. For test purposes, the unassigned input can be turned on and off through the context menu with the right mouse button. This allows, among other things, testing of program sequences with unavailable hardware. If several objects were instanced, it is important to ensure that the right network is selected. Go offline and restore the connection to the hardware. Compile and load the project to the control with Download Project & Run. Page 8 18.05.2015

BRIEF LADDER LOGIC OVERVIEW 1.3 Ladder Logic Tools 1.3.1 Contact Types (Contact) Contact Example application: Closed Contact Example application: 18.05.2015 Page 9

BRIEF LADDER LOGIC OVERVIEW Positive Transition The contact used to recognize a positive flank is 1 if, with the last evaluation of the contact, a signal change from 0 to 1 has occurred. The status of this contact remains the same as long as the object is set for which the contact plan network is used. Example application: Negative Transition The contact used to recognize a negative flank is 1 if, with the last evaluation of the contact, a signal change from 1 to 0 has occurred. The status of this contact remains the same as long as the object is set for which the contact plan network is used. Example application: Page 10 18.05.2015

BRIEF LADDER LOGIC OVERVIEW 1.3.2 Coil Types (Coil) Coil Example application: Negated Coil Example application: Set Coil This coil is set to 1 when the status of the left current path is 1. When the left current path changes to 0, the value of this coil remains 1. 18.05.2015 Page 11

BRIEF LADDER LOGIC OVERVIEW Reset Coil With the Reset coil, a coil set using Set Coil can be reset to 0. Example application: When using the ladder logic tools Memory Coil, Set Memory Coil and Reset Memory Coil, the RAM class must be imported from the library. Otherwise the following error message appears in the output window when one of these coils is placed. Memory Coil The Memory coil saves the status of the left current path before a restart. After the CPU is restarted, the value is retained in the memory coil for the duration of the object cycle time. Example application: To use the function, at least one input (contact) must be assigned the name "Memory Coil". This applies to the coils "Set" or "Reset Memory Coil". Page 12 18.05.2015

BRIEF LADDER LOGIC OVERVIEW Set Memory Coil This coil is the same as the Set Coil, except that since the value is stored in the RAM, it also retains the status after the CPU is restarted. Reset Memory Coil This coil is the same as the Reset Coil, except that since the value is stored in the RAM, it also retains the status after the CPU is restarted. Example application: Positive Transition This coil recognizes a positive flank on the left current path and sets the right path to one for a single cycle (Note: cycle time of object). 18.05.2015 Page 13

BRIEF LADDER LOGIC OVERVIEW Negative Transition This coil recognizes a negative flank on the left current path and sets the right path to one for a single cycle (Note: cycle time of object). Example application: Page 14 18.05.2015

BRIEF LADDER LOGIC OVERVIEW 1.4 Additional Ladder Logic Tools Jump With the Jump instruction, a conditional jump to a section of the circuit identified by a label is made. The jump instruction is always drawn toward the right frame. Label If a part of a circuit called from a different program location with a jump instruction, it must be identified with a label. The label is always placed in the left frame. Return Here, the processing of the contact plan is interrupted. 18.05.2015 Page 15

BRIEF LADDER LOGIC OVERVIEW Insert New Row With this option, a new line can be added to the ladder diagram. Delete Empty Row This option is used to delete an empty line in the contact plan. 1.5 Inputs and/or Outputs as Alarm displays In the ladder diagram, a switch element can be optically identified when it is active. For this purpose, set the AlarmObject property to true. The element is then displayed with a red background (in online mode). 1.5.1 Task: AND Gate with Alarm Display Using ladder logic, an AND gate with two inputs and an output is created. The object created is then connected to the inputs and outputs of the S-DIAS set. 1.5.1.1 Create a Class Create an additional Ladder Diagram class with a cyclic task of 100 ms, assign it the name ANDFunction and connect it to the ladder diagram as follows: Page 16 18.05.2015

BRIEF LADDER LOGIC OVERVIEW Select the output with the mouse and in the Properties window, set AlarmObject to true. If the output should be inverted, the Alarm inverted property can be set to true in the properties window. Using the IO Connection Manager, connect the Input and Input1 clients to the hardware inputs Switch3 and Switch4 of the DI202 module. Compile and load the project to the control with Download Project & Run. If both the Switch3 (input) and Switch4 (input1) buttons are pressed in online mode, the output appears with a red background. 1.6 Switch Status Display in the Ladder Diagram In the ladder diagram, the connections can be displayed in different colors depending on the state of the connection. 18.05.2015 Page 17

BRIEF LADDER LOGIC OVERVIEW As long as the inputs are off, the background color is white in both on and offline mode. If the inputs are enabled, the active element has a green background. The following diagram shows the second input, when the first input is reset to 0. It is displayed in a blue field. This means that the second input is still set, because the current circuit was interrupted however, it is no longer supplied with voltage. Outputs can also be created as alarms. If these are activated, the field is red instead of green. Page 18 18.05.2015

BRIEF LADDER LOGIC OVERVIEW 1.7 Using Objects in Ladder Logic from the Library If objects of a library class are used in a ladder diagram, no cyclic time can be set for them. These objects are called in the time period of the object containing the contact plan. To link classes programmed in structured text or IL, a server from the class must have a Read method. The read method is called by the Ladder logic class automatically. 1.7.1 "RS-FlipFlop" Task In the next example, an output in the ladder diagram should be switched by an "RSFlipFlop". Save the project under: C:\SigmatekWorkshop and assign it the name LadderExample2. Go online with the control and load the hardware from the S-DIAS set using the hardware editor. Compile the project (F9) and download it to the PLC. Next, create a Ladder Diagram class and assign it the name SetInOut. In the Properties window, set Cyclic Task to true and assign a Default Cyclic Time of 100 ms. 18.05.2015 Page 19

BRIEF LADDER LOGIC OVERVIEW Create a network with the name LadderNet and place an object of the class SetInOut. Load the Tools library into the project. Page 20 18.05.2015

BRIEF LADDER LOGIC OVERVIEW Open the SetInOut1 network and place two inputs as shown in the following screenshot: Drag & Drop the FlipFlopRS class from the Tools library into the project. 18.05.2015 Page 21

BRIEF LADDER LOGIC OVERVIEW The Import Class dialog window then opens. Exit the default settings and confirm the selection with OK. Connect the two inputs (Input and Input1) with Set or Reset and add an output (Coil). Page 22 18.05.2015

BRIEF LADDER LOGIC OVERVIEW Change to the LadderNet network and connect the inputs and output to the respective in and outputs using the IO Connection Manager. Compile and load the project to the control with Download Project & Run. Perform a function test. When button 2 is pressed, the output is enabled. When no input is active, the output remains enabled. When button 1 is pressed, the output is disabled. 18.05.2015 Page 23