Connecting to Siemens SIMIT

The SIMIT plugin and the Visual Components coupling allows user to connect to the SIMIT real-time behavior emulator software.

SIMIT connection overview

The communication between VC and SIMIT is achieved using two software components.

• Visual Components coupling. An external coupling for SIMIT, also called “VC coupling” for short.
• SIMIT Connection plugin for VC, or “SIMIT plugin” for short.

Both are developed by Visual Components and are only meant to be used with corresponding versions of each other.

Main features of the VC coupling

• Support for multiple parallel local and remote connections over TCP/IP
• Free definition of accessible IO signals
• Signal value change events for efficient data flow from SIMIT to VC
• Asynchronous: Communication delay doesn’t slow down SIMIT

Main features of the SIMIT Connection plugin

• Supports multiple parallel connections
• Free signal browsing and pairing workflow like other Connection plugins
• Automatic SIMIT runtime connection management
• Supports cyclic and event-based update modes
• Asynchronous: Communication delay doesn’t slow down VC

Visual Components coupling

The VC coupling is an external coupling for SIMIT.

Note: The demo version of the SIMIT does not support external couplings.

Delivery and installation

The VC coupling is delivered as a zip file containing a folder containing the coupling’s executable and any other files it needs. To install the coupling, you need to copy the folder to SIMIT’s installation folder path like below:

C:\Program Files (x86)\Siemens\Automation\SIMIT\SIMIT SF\couplings

Note: The coupling’s folder name under “couplings” defines the name of the coupling in SIMIT.

The VC coupling has some limitations stemming from the limitations of the SIMIT external coupling API:

• VC can only access signals defined in the coupling.
• If communication between couplings is desired, all signals must be connected through,e.g., connector blocks in charts.
• Single instance of the VC coupling is supported per SIMIT project.
• The configuration server starts when the coupling is opened.
• The SIMIT SP’s UI and external coupling API provide very limited capabilities for defining the coupling signals within SIMIT. Separate signal editor UI has to be used.

Input and output terminology in SIMIT

In SIMIT, the terms input signal and output signal are always defined such that they refer to the inputs and outputs of the coupling partner, i.e., the hardware or software the coupling connects to. This means that an “input signal” is output and write-only in SIMIT charts.

SIMIT  plugin connection and signal value exchange

The connection to the SIMIT SP editor (configuration server) and the simit simulation (runtime) are separate.     You can connect to SIMIT (editor/configuration server) only after the coupling in SIMIT SP is opened. Therefore loading a project with the coupling is not enough. The connection to the SIMIT simulation is automatically managed when you have the connection to SIMIT SP (editor). The below steps will be a generic step by step configuration guide for establishing the connection.

Adding Visual Components Coupling to SIMIT

1. Launch your SIMIT SP application project.
2. From the Project navigation, under your project, expand Couplings folder.
3. Right-click on New coupling and select New coupling.
4. Select Visual Components under Extern.

Visual Components Coupling UI in SIMIT

• There are eight available time slices as well. Input/Output signal calculation is performed, and the signal value is exchanged with the Visual Components app with this cycle time. For more information, refer to the next section on this topic.

Connectivity tab in Visual Components UI

1. Connect from VC to SIMIT under Connectivity tab.
2. Connect the signals between Visual Components and SIMIT (use the “Pairing variables” article available in Visual Components Help file under Task>Connectivity).

Note: If you start VC simulation first and SIMIT simulation second, all variable pairs will get errors until the SIMIT simulation is started, and connection to it is (automatically) established. Thus, it is recommended to start SIMIT simulation first. Since the connections are separate, in rare cases, they can fail independently.

Signal value exchange between SIMIT communication plugin and Visual Components coupling

The value change event implementation has the features of supporting multiple parallel listeners and avoiding a wildly growing buffer of old messages. However, a significant drawback is that if there is any communication delay spike, value change events will be lost.    

Since the communication of the VC coupling is done asynchronously, it doesn’t provide accurate load information to SIMIT. The gateway load only represents the time taken by the signal value cache update only, which can be occasionally blocked for the duration of the read and write request processing.   

Performance

It is highly recommended to use:

• Cyclic update mode for simulation to server variable groups
  • Choose a cycle interval that is same or higher than the time slice used for the VC coupling the SIMIT project.
  • Sending values to SIMIT at a rate faster than the VC coupling’s update cycle doesn’t give any benefit, which includes the event-based mode in this direction.
• Event-based update mode for server to simulation variable groups
  • SIMIT will try to send value updates at the rate of the VC coupling’s time slice. Only if this rate is unnecessarily high or the data flow is overwhelming VC, it is recommended to switch to a lower sampling rate using cyclic update mode.
  • See also notes about skipped value updates from previous section.

Note: The time slice of the VC coupling should be set to a reasonable value. For example, there isn’t a point in updating the coupling faster than the SIMIT charts that provide or use the data. For visualization, 60 Hz is the generally accepted refresh rate for very smooth animation, and 30 Hz being good enough for most purposes.