SIMIT Scripting Modes (Synchronous vs Asynchronous) and Password-Protected Library Components

In SIMIT Simulation Framework (SF), automated test scripts can only be created when the simulation operates in Asynchronous mode. The Synchronous operating mode—which supports As Fast As Possible (AFAP) time acceleration—precludes script generation because unconstrained solver execution conflicts with the deterministic event scheduling required by the SIMIT scripting engine. Furthermore, standard library components (such as FLOWNET and CONTEC drivers) are proprietary Siemens intellectual property protected by non-disclosed passwords in the Component Type Editor (CTE). When simulations become physically unstable under extreme acceleration (>500%), the root cause is fixed-step numerical integration divergence in differential equations, which requires reducing integration time slices rather than modifying source code.

SIMIT Simulation Execution Modes: Synchronous vs Asynchronous

SIMIT provides two distinct modes for executing simulation scan cycles:

Asynchronous Mode (Wall-Clock Synchronized): The simulation calculation engine is coupled to real-time wall clock intervals (e.g., executing a 100 ms time slice every 100 ms). SIMIT automated test scripts execute in an independent thread, evaluating conditions, asserting inputs, and measuring plant responses deterministically.
Synchronous Mode (As Fast As Possible - AFAP): The simulation solver is completely decoupled from real-time clocks. As soon as one calculation step concludes, the next step begins immediately. This enables rapid multi-hour scenario execution, virtual commissioning batch validation, and model training.

Why Scripting Is Restricted in AFAP Mode

The table below contrasts operational constraints between the two execution modes:

Feature / CapabilityAsynchronous ModeSynchronous Mode (AFAP)Time CouplingTied to physical wall clock / fixed time scale.Decoupled; executes as fast as CPU permits.Scripting SupportFully Supported: Scripts execute deterministically.Restricted / Blocked: Race conditions between script engine and solver.External CouplingsPLCSIM, SIMIT UNIT, OPC DA/UA active.External hardware/bus couplings generally disabled.Solver StabilityHigh: stable fixed time step integration.Risk of numerical divergence if $\Delta t$ is too large for fast dynamics.

Intellectual Property Protection in SIMIT CTE Library Modules

Standard components provided in the SIMIT basic and industry libraries (FLOWNET, CONTEC, ChemBasic) are pre-compiled, certified behavioral models. Siemens protects these blocks with internal cryptographic passwords to prevent unauthorized tampering, reverse engineering, and warranty disputes.

Engineers cannot retrieve or bypass this password in the Component Type Editor (CTE). To introduce custom behavior, engineers must create a new component from scratch in CTE or utilize open template components provided in the SIMIT Application Examples repository.

Resolving Numerical Instability Under High Acceleration

When a simulation model functions accurately at 100% or 500% time scale but exhibits non-physical values or overflows under AFAP acceleration, the issue is mathematical, not programmatic:

Integration Step Overshoot: Differential equations modeling temperature, pressure, or rotational inertia use discrete numerical solvers ($x_{k+1} = x_k + \Delta t \cdot f(x_k)$). If the time step $\Delta t$ is stretched during acceleration, the numerical integration exceeds physical stability limits, causing exponential divergence.
Remediation: In SIMIT project properties, configure smaller discrete time slices (e.g., reduce time slice from 100 ms to 20 ms or 10 ms). While this increases calculations per simulated second, it maintains strict numerical convergence during AFAP.

Verification

To verify simulation stability and script execution:

Switch the simulation operating mode to Asynchronous.
In the SIMIT project tree, create a new script under Automatic Model Construction / Scripts.
Define step sequences: SET Variable = 1; WAIT 5s; CHECK Feedback == 1;.
Start the simulation: verify that the script executes step-by-step and logs results in the script console.
In Synchronous (AFAP) mode, verify that the solver runs continuously without mathematical singularity errors.

Limitations and Operational Precautions

Operational boundaries when utilizing SIMIT scripting:

External Coupling Lag: If S7-PLCSIM or a physical SIMIT UNIT is connected, AFAP mode cannot be sustained because physical communication layers cannot accelerate beyond real-time bus speeds.
Password Requests Rejected: Siemens Customer Support will not disclose passwords for standard pre-compiled library modules.
Licensing Entitlement: Advanced scripting and CTE development require the SIMIT Engineering license (SIMIT M, L, or XL).

Engineer FAQ

Why does SIMIT forbid scripts in Synchronous AFAP mode?

AFAP mode decouples the solver from time intervals, making it impossible for the script engine to coordinate wait times, condition checks, and signal assertions deterministically.

Can Siemens provide the password to open FLOWNET components in CTE?

No. Standard library components are proprietary compiled IP. Siemens does not release source passwords to end users or system integrators.

Why do physical variables go to infinity when running at AFAP?

Discrete numerical integration algorithms become unstable if time slices are too coarse relative to system dynamics. Decreasing the base calculation cycle time slice restores convergence.

What tool allows creating custom components without passwords?

The Component Type Editor (CTE) allows engineers to create original, fully editable custom components that reside in the project's 'User Components' catalog.