Drawing Schematic/Wiring Diagrams Using CAD Software

Computer-Aided Design (CAD) software is computer applications that help in creating, modifying, analyzing, and optimizing a design. CAD software is commonly used by engineers (mechanical, electrical, and computer engineers, among others) and in other fields that involve drawing. The need for CAD in industrial automation cannot be over-emphasized as designs or control systems need to be created, modified, analyzed, and optimized on a computer to achieve the desired result. Examples of CAD software include AutoCAD, ProfiCAD, PCSCHEMATIC Automation, Automation Studio, SmartDraw, and so on. In engineering or industrial automation-related drawing, CAD software saves time and drawings are more accurate than when using manual methods.

This chapter explains the use of the PCSCHEMATIC Automation software to draw schematic/wiring diagrams relating to industrial automation. We will learn how to create a control system drawing using the software...

Technical requirements

Our focus in this chapter is the use of CAD software (PCSCHEMATIC Automation) to draw circuit/schematic diagrams.

While efforts were made to make the chapter comprehensive for readers without the knowledge of the previous chapters, knowledge of Chapter 4, Overview Of AC and DC Motors, will be of help.

Steps to install the CAD software (PCSCHEMATIC Automation) will be provided in this chapter. You will need a computer system or laptop with the following minimum system requirements:

• Operating system: Windows XP/Vista/7/8.1/10
• Memory (RAM): 1 GB of RAM
• Hard disk space: 400 MB of free space
• Processor: Intel Pentium 4 or later

Understanding electrical diagrams/drawings

Before we start to learn how to draw schematics with CAD, let’s get an understanding of the various types of electrical drawings/diagrams you are likely to come across in industrial automation and control.

Common electrical drawings/diagrams in industrial automation and control include the following:

• Schematic diagrams can be referred to as electrical diagrams that show the components in a circuit using standard symbols and also how they connect with each other but do not include where the components and wires are located in the real system or device:

Figure 6.1 – Schematic diagram of a Direct On-Line (DOL) starter

• Wiring diagrams are electrical diagrams that show the components involved in a circuit, the physical connections between the components, and where the components and wires are located in the real system or device, unlike schematic diagrams, which do not show the real...

9 Understanding Programmable Logic Controller – Part 3

In the previous chapter, we learnt the fundamentals of PLC programming which include PLC programming languages, PLC programming devices, PLC programming software, Ladder Diagram basics, elements of Ladder Diagram (ladder logic program), rules for Ladder Diagram programming, downloading and installing TIA Portal V13 professional and PLCSIM, and how to create a project and write some programs with the programming software (TIA Portal).

In this chapter you will dive deeper by practicing how to use the programming software you downloaded and installed in the previous chapter. This chapter also includes simulation of programs which will enable you to see the result of the programs you have written right there on your PC or laptop even when you don’t have the real PLC to test or practice.

We are going to cover the following main topics in this chapter:

• Opening a saved program
• Simulating programs with Siemens TIA portal using...

Technical requirements

While every part of this book is valuable, Chapter 2, Switches and Sensors: Working Principles, Applications and Wiring, Chapter 3, Actuators and Their Applications in industrial automation and Chapter 7, Understanding Programmable Logic Controller-Part 1 as well as Chapter 8, Understanding Programmable Logic Controllers-Part 2 are very important to have a better understanding of this chapter.

This chapter is actually a continuation of the previous chapter. Hence, you must have familiarized yourself with the necessary terms and the programming software (TIA Portal) and also practiced the programs explained using necessary instructions before reading this chapter.

Opening a saved program

We will continue learning the programming of PLC here by opening the project/program we saved in the previous chapter:

1. Start the TIA Portal application

2. Click on Open existing project and select the project and click Open:

   

   Figure 9.1 – Opening a saved program – recently used project

3. On clicking Open, you should see the following, click on Open the project view:

   

   Figure 9.2 – Opening a saved program – Open the project view

4. Double click the PLC in the device list at the left hand side of the screen, PLC_1 [CPU1211C AC/DC/Rly] and double click Program blocks:

   

   Figure 9.3 – Opening a saved program – PLC_1 [CPU1211C AC/DC/Rly]

5. Double click Main [OB1]:

   

   Figure 9.4 – Opening a saved program – Main [OB1]

   The program will be opened showing the ladder diagram as shown in the following screenshot:

Figure 9.5 – Program opened showing the Ladder Diagram

We have just learnt how to open a saved program in...

Simulating programs with Siemens TIA Portal using PLCSIM

We will now learn how to simulate a program using Siemens TIA portal. We will use the program written in the previous chapter as an example:

1. Open the project/program using the steps in the previous section. You should have what looks like the following screenshot. Click on the Compile icon and ensure there is no error in your program:

   

   Figure 9.6 – Opened project showing compile button (red arrow)

2. Click on the Start simulator icon as indicated in the following screenshot:

   

   Figure 9.7 – Compiled program showing no error that is, 0 errors

3. A warning message shown as follows will appear. Click OK:

   

   Figure 9.8 – Simulating program – Warning message

   You should have what looks similar to the following screenshot:

   

   Figure 9.9 – Simulating program – Extended download to device dialog box

4. Select PLCSIM S7-1200/S7-1500 in the PG/PC interface list and click Start search. Select CPUcommon with address...

Latching and unlatching in PLC programming

Latching is a technique used to keep an output energized or activated even when the input ceases. Latching makes a momentary push button act as a maintained switch i.e. after the push button is pressed, the output it turned on remain energized (ON) even when the button is released.

Unlatching is simply a method or technique used to de-energize a latched output.

Latch and unlatch program using normally open push buttons for both start and stop

Write the simple program in network 3 to see how latching and unlatching works with normally open push button for start and normally open push button for stop:

Figure 9.27 – Latch and unlatch program using normally open push buttons for both start and stop

The PLC wiring for the program is as follows:

Figure 9.28 – Wiring to implement latch & unlatch program with normally open push buttons used for both start and stop

The preceding wiring diagram in shows the start push button (normally...

Using output address for an input in a program

• In the previous chapter we learnt that output address can be used as input address (NC or NO contact) in the rules for ladder diagram programming.
• The following example shows an output address (Q0.2) being used for an input. You can write the program in network 4 and simulate the program to see how it works:

Figure 9.31 – Output address (Q0.2) used for a normally open contact at input

The wiring diagram for the program is as follows:

Figure 9.32 – Wiring diagram to implement a program using output address for input

Let’s say a pilot lamp (PL3) is connected to Q0.3 as shown in the preceding figure.

Anytime Q0.2 is ON, the normally open contact with address Q0.2 will be closed since the coil with address Q0.2 is energized and PL3 connected to Q0.3 will be ON.

If we edit the program by replacing the normally open contact with address Q0.2 with a normally closed contact as shown in the following screenshot, the program...

Using the SET and RESET instructions

The SET and RESET instructions are two important instructions used in Ladder Diagram programming. They are both output (coil/assignment) instructions.

The SET coil is energized when power is supplied to it via an input (switch, sensor or push button) and it remains SET (ON) even when the switch, sensor or push button that supplied power to it is OFF until it is reset.

The RESET coil is de-energized (OFF) when power is supplied to it via an input (switch, sensor or push button) and it remains OFF even when the switch, sensor or push button that supplied power to it is OFF until it is SET.

The sample program in the following screenshot shows the SET and RESET instructions in use:

Figure 9.34 – SET and RESET Program

Note

The set/reset instruction can be added to your rung using the following steps:

At the right hand side of the programming environment, click Instructions | Bit Logic operation | Drag the set output instruction or reset output...

Using the timer instruction

The timer instruction is a delay instruction. It can be used to delay an operation. Several timers exist, the common ones are ON-delay timer (TON) and OFF-delay timer (TOF).

An on delay timer (TON) activates an output when the input is ON for a specified amount of time.

Let’s write a simple program to demonstrate on delay timer using the following steps:

1. On a new network, add a normally open instruction and specify an address e.g. I0.0.

2. At the right hand side of the programming environment, click Instructions | Timer operation | Drag TON (ON delay timer) instruction to the rung and type a name, for example, timer1 as shown in the following screenshot. Click OK:

   

3. Figure 9.36 – How to use timer instruction –Call option dialog boxDouble click the question marks (???) at PT (programmed time) and type the time you want Q (output) to become energized, for example, 25s or T#25s.
4. Press Enter twice.
5. Drag a coil/assignment instruction to the output...