Beckhoff TwinCAT 3 for Safety Systems
TwinCAT 3 transforms standard PCs into high-performance real-time controllers, integrating PLC, motion control, and HMI development in Visual Studio. Built on CODESYS V3 with extensive Beckhoff enhancements. TwinCAT's real-time kernel runs alongside Windows achieving cycle times down to 50 microseconds....
Platform Strengths for Safety Systems:
- Extremely fast processing with PC-based control
- Excellent for complex motion control
- Superior real-time performance
- Cost-effective for high-performance applications
Unique ${brand.software} Features:
- Visual Studio integration with IntelliSense and debugging
- C/C++ real-time modules executing alongside IEC 61131-3 code
- EtherCAT master with sub-microsecond synchronization
- TwinCAT Motion integrating NC/CNC/robotics
Key Capabilities:
The TwinCAT 3 environment excels at Safety Systems applications through its extremely fast processing with pc-based control. This is particularly valuable when working with the 5 sensor types typically found in Safety Systems systems, including Safety light curtains, Emergency stop buttons, Safety door switches.
Control Equipment for Safety Systems:
- Safety PLCs (fail-safe controllers)
- Safety relays (configurable or fixed)
- Safety I/O modules with diagnostics
- Safety network protocols (PROFIsafe, CIP Safety)
Beckhoff's controller families for Safety Systems include:
- CX Series: Suitable for advanced Safety Systems applications
- C6015: Suitable for advanced Safety Systems applications
- C6030: Suitable for advanced Safety Systems applications
- C5240: Suitable for advanced Safety Systems applications
Hardware Selection Guidance:
CX series embedded controllers for compact applications. C6015/C6030 IPCs for demanding motion and vision. Panel PCs combine control with displays. Multi-core systems isolate real-time tasks on dedicated cores....
Industry Recognition:
Medium - Popular in packaging, semiconductor, and high-speed automation. XTS linear transport for EV battery assembly. Vision-guided robotics with TwinCAT Vision. Body-in-white welding with sub-millisecond EtherCAT response. Digital twin validation before commissioning....
Investment Considerations:
With $$ pricing, Beckhoff positions itself in the mid-range segment. For Safety Systems projects requiring advanced skill levels and 4-8 weeks development time, the total investment includes hardware, software licensing, training, and ongoing support.
Understanding Function Blocks for Safety Systems
Function Block Diagram (FBD) is a graphical programming language where functions and function blocks are represented as boxes connected by signal lines. Data flows from left to right through the network.
Execution Model:
Blocks execute based on data dependencies - a block executes only when all its inputs are available. Networks execute top to bottom when dependencies allow.
Core Advantages for Safety Systems:
- Visual representation of signal flow: Critical for Safety Systems when handling advanced control logic
- Good for modular programming: Critical for Safety Systems when handling advanced control logic
- Reusable components: Critical for Safety Systems when handling advanced control logic
- Excellent for process control: Critical for Safety Systems when handling advanced control logic
- Good for continuous operations: Critical for Safety Systems when handling advanced control logic
Why Function Blocks Fits Safety Systems:
Safety Systems systems in Universal typically involve:
- Sensors: Emergency stop buttons (Category 0 or 1 stop), Safety light curtains (Type 2 or Type 4), Safety laser scanners for zone detection
- Actuators: Safety contactors (mirror contact type), Safe torque off (STO) drives, Safety brake modules
- Complexity: Advanced with challenges including Achieving required safety level with practical architecture
Programming Fundamentals in Function Blocks:
StandardBlocks:
- logic: AND, OR, XOR, NOT - Boolean logic operations
- comparison: EQ, NE, LT, GT, LE, GE - Compare values
- math: ADD, SUB, MUL, DIV, MOD - Arithmetic operations
TimersCounters:
- ton: Timer On-Delay - Output turns ON after preset time
- tof: Timer Off-Delay - Output turns OFF after preset time
- tp: Pulse Timer - Output pulses for preset time
Connections:
- wires: Connect output pins to input pins to pass data
- branches: One output can connect to multiple inputs
- feedback: Outputs can feed back to inputs for state machines
Best Practices for Function Blocks:
- Arrange blocks for clear left-to-right data flow
- Use consistent spacing and alignment for readability
- Label all inputs and outputs with meaningful names
- Create custom FBs for frequently repeated logic patterns
- Minimize wire crossings by careful block placement
Common Mistakes to Avoid:
- Creating feedback loops without proper initialization
- Connecting incompatible data types
- Not considering execution order dependencies
- Overcrowding networks making them hard to read
Typical Applications:
1. HVAC control: Directly applicable to Safety Systems
2. Temperature control: Related control patterns
3. Flow control: Related control patterns
4. Batch processing: Related control patterns
Understanding these fundamentals prepares you to implement effective Function Blocks solutions for Safety Systems using Beckhoff TwinCAT 3.
Implementing Safety Systems with Function Blocks
Safety system control uses safety-rated PLCs and components to protect personnel and equipment from hazardous conditions. These systems implement safety functions per IEC 62443 and ISO 13849 standards with redundancy and diagnostics.
This walkthrough demonstrates practical implementation using Beckhoff TwinCAT 3 and Function Blocks programming.
System Requirements:
A typical Safety Systems implementation includes:
Input Devices (Sensors):
1. Emergency stop buttons (Category 0 or 1 stop): Critical for monitoring system state
2. Safety light curtains (Type 2 or Type 4): Critical for monitoring system state
3. Safety laser scanners for zone detection: Critical for monitoring system state
4. Safety interlock switches (tongue, hinged, trapped key): Critical for monitoring system state
5. Safety mats and edges: Critical for monitoring system state
Output Devices (Actuators):
1. Safety contactors (mirror contact type): Primary control output
2. Safe torque off (STO) drives: Supporting control function
3. Safety brake modules: Supporting control function
4. Lock-out valve manifolds: Supporting control function
5. Safety relay outputs: Supporting control function
Control Equipment:
- Safety PLCs (fail-safe controllers)
- Safety relays (configurable or fixed)
- Safety I/O modules with diagnostics
- Safety network protocols (PROFIsafe, CIP Safety)
Control Strategies for Safety Systems:
1. Primary Control: Safety-rated PLC programming for personnel protection, emergency stops, and safety interlocks per IEC 61508/61511.
2. Safety Interlocks: Preventing Safety integrity level (SIL) compliance
3. Error Recovery: Handling Redundancy requirements
Implementation Steps:
Step 1: Perform hazard analysis and risk assessment
In TwinCAT 3, perform hazard analysis and risk assessment.
Step 2: Determine required safety level (SIL/PL) for each function
In TwinCAT 3, determine required safety level (sil/pl) for each function.
Step 3: Select certified safety components meeting requirements
In TwinCAT 3, select certified safety components meeting requirements.
Step 4: Design safety circuit architecture per category requirements
In TwinCAT 3, design safety circuit architecture per category requirements.
Step 5: Implement safety logic in certified safety PLC/relay
In TwinCAT 3, implement safety logic in certified safety plc/relay.
Step 6: Add diagnostics and proof test provisions
In TwinCAT 3, add diagnostics and proof test provisions.
Beckhoff Function Design:
FB design extends with C# patterns. Methods group operations. Properties enable controlled access. Interfaces define contracts for polymorphism. The EXTENDS keyword creates inheritance.
Common Challenges and Solutions:
1. Achieving required safety level with practical architecture
- Solution: Function Blocks addresses this through Visual representation of signal flow.
2. Managing nuisance trips while maintaining safety
- Solution: Function Blocks addresses this through Good for modular programming.
3. Integrating safety with production efficiency
- Solution: Function Blocks addresses this through Reusable components.
4. Documenting compliance with multiple standards
- Solution: Function Blocks addresses this through Excellent for process control.
Safety Considerations:
- Use only certified safety components and PLCs
- Implement dual-channel monitoring per category requirements
- Add diagnostic coverage to detect latent faults
- Design for fail-safe operation (de-energize to trip)
- Provide regular proof testing of safety functions
Performance Metrics:
- Scan Time: Optimize for 5 inputs and 4 outputs
- Memory Usage: Efficient data structures for CX Series capabilities
- Response Time: Meeting Universal requirements for Safety Systems
Beckhoff Diagnostic Tools:
Visual Studio debugger with breakpoints and watch windows,Conditional breakpoints stopping on expression true,Scope view recording variables with triggers,EtherCAT diagnostics showing slave status and errors,Task execution graphs showing cycle time variations
Beckhoff's TwinCAT 3 provides tools for performance monitoring and optimization, essential for achieving the 4-8 weeks development timeline while maintaining code quality.
Beckhoff Function Blocks Example for Safety Systems
Complete working example demonstrating Function Blocks implementation for Safety Systems using Beckhoff TwinCAT 3. Follows Beckhoff naming conventions. Tested on CX Series hardware.
(* Beckhoff TwinCAT 3 - Safety Systems Control *)
(* Reusable Function Blocks Implementation *)
(* FB design extends with C# patterns. Methods group operations *)
FUNCTION_BLOCK FB_SAFETY_SYSTEMS_Controller
VAR_INPUT
bEnable : BOOL; (* Enable control *)
bReset : BOOL; (* Fault reset *)
rProcessValue : REAL; (* Emergency stop buttons (Category 0 or 1 stop) *)
rSetpoint : REAL := 100.0; (* Target value *)
bEmergencyStop : BOOL; (* Safety input *)
END_VAR
VAR_OUTPUT
rControlOutput : REAL; (* Safety contactors (mirror contact type) *)
bRunning : BOOL; (* Process active *)
bComplete : BOOL; (* Cycle complete *)
bFault : BOOL; (* Fault status *)
nFaultCode : INT; (* Diagnostic code *)
END_VAR
VAR
(* Internal Function Blocks *)
fbSafety : FB_SafetyMonitor; (* Safety logic *)
fbRamp : FB_RampGenerator; (* Soft start/stop *)
fbPID : FB_PIDController; (* Process control *)
fbDiag : FB_Diagnostics; (* FB_AlarmHandler with Raise(), Clear(), Acknowledge() methods. Internal storage tracks activation time and acknowledgment state. Integration with TwinCAT EventLogger. *)
(* Internal State *)
eInternalState : E_ControlState;
tonWatchdog : TON;
END_VAR
(* Safety Monitor - Use only certified safety components and PLCs *)
fbSafety(
Enable := bEnable,
EmergencyStop := bEmergencyStop,
ProcessValue := rProcessValue,
HighLimit := rSetpoint * 1.2,
LowLimit := rSetpoint * 0.1
);
(* Main Control Logic *)
IF fbSafety.SafeToRun THEN
(* Ramp Generator - Prevents startup surge *)
fbRamp(
Enable := bEnable,
TargetValue := rSetpoint,
RampRate := 20.0, (* Universal rate *)
CurrentValue => rSetpoint
);
(* PID Controller - Process regulation *)
fbPID(
Enable := fbRamp.InPosition,
ProcessValue := rProcessValue,
Setpoint := fbRamp.CurrentValue,
Kp := 1.0,
Ki := 0.1,
Kd := 0.05,
OutputMin := 0.0,
OutputMax := 100.0
);
rControlOutput := fbPID.Output;
bRunning := TRUE;
bFault := FALSE;
nFaultCode := 0;
ELSE
(* Safe State - Implement dual-channel monitoring per category requirements *)
rControlOutput := 0.0;
bRunning := FALSE;
bFault := NOT bEnable; (* Only fault if not intentional stop *)
nFaultCode := fbSafety.FaultCode;
END_IF;
(* Diagnostics - Circular buffer with nWriteIdx modulo operation. File export using FB_FileWrite from Tc2_System. Triggered capture preserving pre-trigger data. *)
fbDiag(
ProcessRunning := bRunning,
FaultActive := bFault,
ProcessValue := rProcessValue,
ControlOutput := rControlOutput
);
(* Watchdog - Detects frozen control *)
tonWatchdog(IN := bRunning AND NOT fbPID.OutputChanging, PT := T#10S);
IF tonWatchdog.Q THEN
bFault := TRUE;
nFaultCode := 99; (* Watchdog fault *)
END_IF;
(* Reset Logic *)
IF bReset AND NOT bEmergencyStop THEN
bFault := FALSE;
nFaultCode := 0;
fbDiag.ClearAlarms();
END_IF;
END_FUNCTION_BLOCKCode Explanation:
- 1.Encapsulated function block follows FB design extends with C# patterns. Meth - reusable across Universal projects
- 2.FB_SafetyMonitor provides Use only certified safety components and PLCs including high/low limits
- 3.FB_RampGenerator prevents startup issues common in Safety Systems systems
- 4.FB_PIDController tuned for Universal: Kp=1.0, Ki=0.1
- 5.Watchdog timer detects frozen control - critical for advanced Safety Systems reliability
- 6.Diagnostic function block enables Circular buffer with nWriteIdx modulo operation. File export using FB_FileWrite from Tc2_System. Triggered capture preserving pre-trigger data. and FB_AlarmHandler with Raise(), Clear(), Acknowledge() methods. Internal storage tracks activation time and acknowledgment state. Integration with TwinCAT EventLogger.
Best Practices
- ✓Follow Beckhoff naming conventions: Prefixes: b=BOOL, n=INT, f=REAL, s=STRING, st=STRUCT, e=ENUM, fb=FB instance. G_
- ✓Beckhoff function design: FB design extends with C# patterns. Methods group operations. Properties enable
- ✓Data organization: DUTs define custom types with STRUCT, ENUM, UNION. GVLs group globals with pragm
- ✓Function Blocks: Arrange blocks for clear left-to-right data flow
- ✓Function Blocks: Use consistent spacing and alignment for readability
- ✓Function Blocks: Label all inputs and outputs with meaningful names
- ✓Safety Systems: Keep safety logic simple and auditable
- ✓Safety Systems: Use certified function blocks from safety PLC vendor
- ✓Safety Systems: Implement cross-monitoring between channels
- ✓Debug with TwinCAT 3: Use F_GetTaskCycleTime() verifying execution time
- ✓Safety: Use only certified safety components and PLCs
- ✓Use TwinCAT 3 simulation tools to test Safety Systems logic before deployment
Common Pitfalls to Avoid
- ⚠Function Blocks: Creating feedback loops without proper initialization
- ⚠Function Blocks: Connecting incompatible data types
- ⚠Function Blocks: Not considering execution order dependencies
- ⚠Beckhoff common error: ADS Error 1793: Service not supported
- ⚠Safety Systems: Achieving required safety level with practical architecture
- ⚠Safety Systems: Managing nuisance trips while maintaining safety
- ⚠Neglecting to validate Emergency stop buttons (Category 0 or 1 stop) leads to control errors
- ⚠Insufficient comments make Function Blocks programs unmaintainable over time