LADSIM - Ladder Logic Simulator

LADSIM is a fully functional ladder logic design and PLC simulation software program that incorporates the functions used in PLC ladder programming. LADSIM uses the PC as a virtual PLC.

Figure 1. LADSIM Interface

There are three main screen of LADSIM:

1. The Ladder Logic Diagram Window

This is where the ladder code is displayed. Each time you add or edit a rung, the result will be shown here.

Rung is serves as conditioning for command input and output logic.

2. The Controls box.

This contains the ladder symbols that are used to create the ladder diagram. See below for further details.

3. The toolbar

This includes the standard buttons of LADSIM and allows you to start a new diagram, open an existing file, print, save and comment your ladder diagram.

You aso can apply your ladder code to run simulations in LADSIM. These simulations are:

1. Traffic Light

Code must be written to control the sequence of operation of the lights. A typical sequence could be : RED 'ON' immediately After 2 seconds YELLOW 'ON' After 3 seconds GREEN 'ON' only After 5 seconds YELLOW 'ON' only After 1 second Restart Sequence. The task would be to code this sequence in ladder logic and operate the lights accordingly.

2. The Annunciator

In industry, plant conditions need to be monitored and, if there are problems, a way of indicating these problems. An indicator system of this type is called an annunciator. A typical alarm system uses the following sequence to indicate a plant alarm condition to an operator. System healthy - no indication. System in alarm - a flashing light and audible alarm.

The annunciator in LADSIM must be programmed to allow the correct operation.

3. The Car Park

The diagram shows the layout of a simple car park. It has an entry barrier and an exit barrier. The car park itself has six spaces and a series of displays to indicate whether it is full, has spaces or is empty, with a numerical indicator to determine the exact amount.

Ladder code needs to be written that will allow cars into the car park when it is empty or has spaces and to exit the car park through the correct barrier. Ladder code must also be written to control the display boxes in the centre of the screen.

4. The Lift (Elevator)

A program is required that will drive the lift from one floor to the other on a signal from the call button. Safety is essential and we must be careful not to have anything obstructing the operation of the doors.

5. The Drinks Machine

When a coin is placed into the slot, the user should be able to select his or her favourite drink or reject the coin. It is important to ensure that the coin cannot be rejected once a drink has been selected or that selecting a drink disables all of the other drink buttons.

6. The Packing Line

The packing line carries boxes of different sizes which need to be separated into their relevant sizes.

Which direction the boxes go is decided by using the input sensors IP0 and IP1. If a box is short, only one of the inputs is energised at any one time. If it is a long box, then both inputs will be energised. These results can then be used to activate the correct solenoid and the direction of rotation of the circular plate.

7. The Bottling Plant

The graphic is an overview of a simplified bottling plant with a filling station and packing area. Bottles are fed along the first conveyor, conveyor 1, into the filling station. The bottles must be stopped and filled with milk and then have a cap placed on them. Once accomplished, they go onto conveyor 2 where the cap is screwed on tight. They are finally stacked in the stacker area where they are pushed onto conveyor 3.