Overview

In Siemens SIMATIC Manager (Step 7), programming with Normally Open (NO) and Normally Closed (NC) contacts in Ladder Logic is fundamental for creating control circuits. Here's how to effectively use these contacts

🔘 Normally Open (NO) Contacts

Symbol: - | | -

Function: Allows current to flow when the associated condition is TRUE (bit is 1).

Use Case: Commonly used for start buttons or conditions that enable an output when active.

Example:

ladder
| I0.0 | Q0.0 |

In this rung, if input I0.0 is TRUE (1), the output Q0.0 will be activated.

🔁 Normally Closed (NC) Contacts

Symbol: - |/| -Electronics Tutorials

Function: Allows current to flow when the associated condition is FALSE (bit is 0).

Use Case: Often used for stop buttons or safety interlocks, where the output should be active when the condition is not met.

Example:

ladder
| I0.1 | Q0.0 |

Here, if input I0.1 is FALSE (0), the output Q0.0 will be activated.

🔗 Combining NO and NC Contacts

You can combine NO and NC contacts in series or parallel to create more complex logic:

• Series (AND Logic): All conditions must be TRUE for the output to activate.

• Parallel (OR Logic): At least one condition must be TRUE for the output to activate.

Example:

ladder
| I0.0 | I0.1 | Q0.0 |

In this rung, if both I0.0 and I0.1 are TRUE, Q0.0 will be activated.

🛠️ Programming in SIMATIC Manager

1. Open SIMATIC Manager: Launch the software and navigate to your project.

2. Insert a New Network: Right-click on the desired block (e.g., OB1) and select "Insert New Network."

3. Add Contacts:

   • Click on the "Contacts" button in the toolbar.

   • Choose either NO or NC contact.

   • Click on the rung where you want to place the contact.

4. Assign Variables:

   • Double-click the contact to open its properties.

   • Assign the appropriate variable (e.g., I0.0).

5. Add Coils: At the end of the rung, add a coil to represent the output.

6. Download and Test: After programming, download the block to the PLC and test the logic.