The products of the PLC Simulators line are the basic tools for checking out applications connected to the PLCs. The simulators are compatible with the better known supervisors on the market.
The development of supervision applications and man-machine interface includes, by definition, the involvement of one or more PCs and one or more peripheral units (PLC, CNC, etc.). The functional test of the supervision application, once the peripheral is connected, consists in verifying the compatibility between events (actions) and behaviour (reactions). A simple example could be the link between the colour of a graphic object in a page and a bit of a word of the peripheral. To check whether the graphic object changes colour depending on the bit, a way must be found to modify the bit and the desired effect checked on the video. A PC, a PLC and a hardware signal simulator are required to make these checks; moreover both the supervision application and the PLC program must have been developed.
The PLC communication simulators permit a much more practical and rational approach consisting in the use of two PCs: one for the supervision application and the other to simulate the presence of the peripheral. Operating conveniently on the simulator it is possible to modify the value of words or bits and check the effect on the supervisor. The simulators can simulate several PLCs with a single PC. When systems are to be developed with many PLCs connected to the supervisor, testing out the application becomes even more critical. By using the software simulator it becomes possible to make the supervisor work in very much more similar conditions to the final system ones.
In general, PLCs must comply with certain basic rules of an economic nature:

• they must be purchased as late as possible
• when they arrive they must be immediately fitted to the panel
• they must be delivered to the Customer as soon as they are fitted to the panel

Even if intending to infringe some of these rules, it is important to remember that, for complex systems, the physical presence of three, four, five or more PLCs is, in any case, limited at the time of installation.
Since the simulator makes the test phase possible even without PLCs, the development of the supervision application is not constrained by the actual availability of the PLC.
The use of a PLC communication software simulator is extremely simple. It does not even require specific knowledge of PLC programming. The simulator makes few demands in terms of CPU and memory: a 386 is adequate to operate it without major problems.
The software simulator allows one to be immediately operational; there is no need to bind the start of work for developing the supervision application to the availability of the PLC.
It is easy to fine-tune the supervision software with a simulator. It is extremely simple to change the type of peripheral; it is even possible to simulate PLC networks on a single serial line.
When systems with many PLCs are to be dealt with, simulators allow the system to be perfected right from the development stage. Once the system is installed, simulators become indispensable to permit continuing testing in the case of malfunctions encountered directly or suffered by the end user.
Since they are external peripheral simulators, they can be potentially used with any man-machine interface or supervision system. They can be equally useful for those who develop their own software or for those who use operator terminals dialoguing with PLCs. PLC communication simulators allow the values of the internal PLC resources (words, flags, etc.) to be displayed efficiently. In general, simulators permit:

• Connection to the supervisor via serial lines or network
• Management of more than one PLC on the same machine
• Association of the simulated PLCs to one or more communication ports
• Triggering simulation of the process via MicroC programs
• Record the configuration currently in use to disk
• Quickly fill areas of resources with predefined values
• Temporarily modify the configuration currently in use
• Record the current values of the resources managed to disk

For each simulated resource Type it is possible to:

• Define which resources to display
• Define the display format
• Define the display colour
• Display the values
• Manually modify the values
• Manually and easily modify the individual bits of the resources defined
• Automatically modify the values with programmable criteria and times

The PLC communication simulators currently available are listed below. Production of simulators, however, is always active. Therefore simulators not mentioned in this list could also be available. Version numbers are not quoted in the list because they are liable to rapid change.

Products available	Peripheral simulated
SimAB	Allen-Bradley PLC
SimABB	ABB T200 e CS31 PLC
SiMITSU	Mitsubishi Melsec-A PLC
SimMbus	Modbus Slave
SimS7	Siemens series S7-200 PLC
SimSAIA	SAIA PLC
Simtex	Texas PLC
Sitach	Hitachi PLC
Somron	Omron PLC
Ssiem	Siemens series S5 PLC