Lab 10: Programmable Logic Controllers and Ladder Logic

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EUT 1040 FDLTCC Spring, 2004

LAB 10: Programmable Logic Controllers and Ladder Logic


To learn how to write Ladder Logic programs for a PLC and test them with a PLC emulator.


Since the late 1960’s, the Automobile Industry has developed programmable control devices to facilitate assembly line changes that accommodate yearly model changes. These programmable devices evolved into the modern Programmable Logic Controller (PLC). A PLC consists of a central processor unit (CPU) that is user programmable. The CPU controls the contact status many Input/Output ports. It is possible, through user written code, to use the PLC to emulate the operation of multiple control relays. The programming language for PLCs has traditionally been standard relay control logic, usually called Relay Ladder Logic (RLL). Today, PLCs are widely used in many industries. It is advantageous for Engineers to be comfortable in applying them to a wide range of industrial controls.

Personal Computer

TriLogic PLC Emulation Software V5.0

Java2 Runtime Environment Software (If not already supported on your PC)
Loading and Simulating an Existing Program:

  1. Launch the WinTriLogic PLC Emulation software from the Start>Programs menu.

(TriLogic takes a significant amount of time to load. If it doesn’t, make sure the Java 2-RE program is running)

  1. Select H-Series PLC Models from the pop-up menu, which will subsequently disappear.

  1. On the main menu bar click File>Open>test1.PC3

  1. The window should now have the following Ladder Logic diagram:

FIGURE 10-1: Program “test1.PC3”

  1. On the main menu bar click Simulate>Run (All I/O Reset). A simulation window will pop-up, showing the “Run” status of all the inputs and outputs.

  1. In the input column, RIGHT CLICK on Switch1. It will turn red, indicating ON.

What happens to the output, Lightbulb? _____________

  1. Now RIGHT CLICK on Switch 2 (both switches will now be ON). What is the effect on Lightbulb? _____________

  1. Left click on Switch1, turning it off. What happens to the Lightbulb? ___________

IF THIS CIRCUIT WERE IN A HOUSE, WHAT WOULD YOU CALL IT? __________________________________

  1. Kill the Simulation window.

Entering a New Ladder Logic Diagram:

  1. On the main menu bar click File>New

  1. The main window will now show a “rail” on the left side, with a red arrow pointing to the first “rung” of the ladder. Press the F2 function key on the keyboard. An I/O Labels window will pop-up. Enter the following Labels:

INPUTS: 1. Stop1

2. Start1

OUTPUTS: 1. GrnLight

2. RedLight

3. Motor

RELAYS: 1. Aux1

2. Mot1

  1. Kill the I/O Labels window and return to the main window. Double-click on the red arrow and a menu bar with relay contacts will appear.

  1. RIGHT CLICK on contact symbol in box 1 (Right Clicking makes the contact Normally Closed - NC) and select the input, Stop1, from the I/O Labels pop-up that appears. The main window should now look like this:

FIGURE 10-2: Entering a Normally Closed Contact

  1. Left Click on the contact symbol in box 1 and select the Input, Start1.

  1. Left Click on the output symbol in box 7 and select the Relay, Aux1 from the I/O Labels pop-up. The main window should now look like this:

FIGURE 10-3: Entering an Output Symbol

  1. Now go back to the Start1 contact and left click on it (it should be highlighted in yellow). Left Click on the parallel contact symbol in box 3 and select the relay, Aux1. This will form a “Self-sealing” relay pick-up. In other words, when the Start1 contact is closed, the Aux1 relay coil will be energized, closing the Aux1 relay contact to “Seal” a current path to the Aux1 coil.

  1. Move down the Rail on the left side and click on it to start a new rung. Continue to add contacts until the Ladder Diagram looks like the figure below:

FIGURE 10-4: Ladder Diagram for a Motor Starting Circuit

  1. In the circuit shown above, the first rung has a self-sealing start button and a stop button that will unseal it. The second rung energizes the motor starting relay coil when the Auxilliary relay in rung 1 is energized. In rung 3, the normally closed contacts of the Aux relay are opened by energizing the aux1 coil, thus turning off the green light. In rung 4, the Mot1 contacts are closed by energizing the Mot1 coil in rung 2, thus starting the motor. In rung 5, the Mot1 contact also energizes the red light.

  1. Go the Simulate>Run (All I/O Reset) and test the operation of the circuit. Does it perform as described? _____________


  1. Write a Ladder Logic program that simulates a 4-Way Light Switch and test it with the TriLogic Simulator. Attach a copy of your Ladder Logic Diagram to this report.

Scott Norr Page 4/22/2016

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