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 Structured Text for Safety Systems
Structured Text (ST) is a high-level, text-based programming language defined in IEC 61131-3. It resembles Pascal and provides powerful constructs for complex algorithms, calculations, and data manipulation.
Execution Model:
Code executes sequentially from top to bottom within each program unit. Variables maintain state between scan cycles unless explicitly reset.
Core Advantages for Safety Systems:
- Powerful for complex logic: Critical for Safety Systems when handling advanced control logic
- Excellent code reusability: Critical for Safety Systems when handling advanced control logic
- Compact code representation: Critical for Safety Systems when handling advanced control logic
- Good for algorithms and calculations: Critical for Safety Systems when handling advanced control logic
- Familiar to software developers: Critical for Safety Systems when handling advanced control logic
Why Structured Text 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 Structured Text:
Variables:
- declaration: VAR / VAR_INPUT / VAR_OUTPUT / VAR_IN_OUT / VAR_GLOBAL sections
- initialization: Variables can be initialized at declaration: Counter : INT := 0;
- constants: VAR CONSTANT section for read-only values
Operators:
- arithmetic: + - * / MOD (modulo)
- comparison: = <> < > <= >=
- logical: AND OR XOR NOT
ControlStructures:
- if: IF condition THEN statements; ELSIF condition THEN statements; ELSE statements; END_IF;
- case: CASE selector OF value1: statements; value2: statements; ELSE statements; END_CASE;
- for: FOR index := start TO end BY step DO statements; END_FOR;
Best Practices for Structured Text:
- Use meaningful variable names with consistent naming conventions
- Initialize all variables at declaration to prevent undefined behavior
- Use enumerated types for state machines instead of magic numbers
- Break complex expressions into intermediate variables for readability
- Use functions for reusable calculations and function blocks for stateful operations
Common Mistakes to Avoid:
- Using = instead of := for assignment (= is comparison)
- Forgetting semicolons at end of statements
- Integer division truncation - use REAL for decimal results
- Infinite loops from incorrect WHILE/REPEAT conditions
Typical Applications:
1. PID control: Directly applicable to Safety Systems
2. Recipe management: Related control patterns
3. Statistical calculations: Related control patterns
4. Data logging: Related control patterns
Understanding these fundamentals prepares you to implement effective Structured Text solutions for Safety Systems using Beckhoff TwinCAT 3.
Implementing Safety Systems with Structured Text
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 Structured Text 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: Structured Text addresses this through Powerful for complex logic.
2. Managing nuisance trips while maintaining safety
- Solution: Structured Text addresses this through Excellent code reusability.
3. Integrating safety with production efficiency
- Solution: Structured Text addresses this through Compact code representation.
4. Documenting compliance with multiple standards
- Solution: Structured Text addresses this through Good for algorithms and calculations.
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 Structured Text Example for Safety Systems
Complete working example demonstrating Structured Text implementation for Safety Systems using Beckhoff TwinCAT 3. Follows Beckhoff naming conventions. Tested on CX Series hardware.
(* Beckhoff TwinCAT 3 - Safety Systems Control *)
(* Structured Text Implementation for Universal *)
(* Prefixes: b=BOOL, n=INT, f=REAL, s=STRING, st=STRUCT, e=ENUM, fb=FB in *)
PROGRAM PRG_SAFETY_SYSTEMS_Control
VAR
(* State Machine Variables *)
eState : E_SAFETY_SYSTEMS_States := IDLE;
bEnable : BOOL := FALSE;
bFaultActive : BOOL := FALSE;
(* Timers *)
tonDebounce : TON;
tonProcessTimeout : TON;
tonFeedbackCheck : TON;
(* Counters *)
ctuCycleCounter : CTU;
(* Process Variables *)
rSafetylightcurtains : REAL := 0.0;
rSafetyrelays : REAL := 0.0;
rSetpoint : REAL := 100.0;
END_VAR
VAR CONSTANT
(* Universal Process Parameters *)
C_DEBOUNCE_TIME : TIME := T#500MS;
C_PROCESS_TIMEOUT : TIME := T#30S;
C_BATCH_SIZE : INT := 50;
END_VAR
(* Input Conditioning *)
tonDebounce(IN := bStartButton, PT := C_DEBOUNCE_TIME);
bEnable := tonDebounce.Q AND NOT bEmergencyStop AND bSafetyOK;
(* Main State Machine - Pattern: TYPE E_State : (IDLE, STARTING, RUNNING, *)
CASE eState OF
IDLE:
rSafetyrelays := 0.0;
ctuCycleCounter(RESET := TRUE);
IF bEnable AND rSafetylightcurtains > 0.0 THEN
eState := STARTING;
END_IF;
STARTING:
(* Ramp up output - Gradual start *)
rSafetyrelays := MIN(rSafetyrelays + 5.0, rSetpoint);
IF rSafetyrelays >= rSetpoint THEN
eState := RUNNING;
END_IF;
RUNNING:
(* Safety Systems active - Safety system control uses safety-rated PLCs and c *)
tonProcessTimeout(IN := TRUE, PT := C_PROCESS_TIMEOUT);
ctuCycleCounter(CU := bCyclePulse, PV := C_BATCH_SIZE);
IF ctuCycleCounter.Q THEN
eState := COMPLETE;
ELSIF tonProcessTimeout.Q THEN
bFaultActive := TRUE;
eState := FAULT;
END_IF;
COMPLETE:
rSafetyrelays := 0.0;
(* Log production data - Circular buffer with nWriteIdx modulo operation. File export using FB_FileWrite from Tc2_System. Triggered capture preserving pre-trigger data. *)
eState := IDLE;
FAULT:
rSafetyrelays := 0.0;
(* FB_AlarmHandler with Raise(), Clear(), Acknowledge() methods. Internal storage tracks activation time and acknowledgment state. Integration with TwinCAT EventLogger. *)
IF bFaultReset AND NOT bEmergencyStop THEN
bFaultActive := FALSE;
eState := IDLE;
END_IF;
END_CASE;
(* Safety Override - Always executes *)
IF bEmergencyStop OR NOT bSafetyOK THEN
rSafetyrelays := 0.0;
eState := FAULT;
bFaultActive := TRUE;
END_IF;
END_PROGRAMCode Explanation:
- 1.Enumerated state machine (TYPE E_State : (IDLE, STARTING, RUNNING, STOPPING, ERROR); CASE eState OF IDLE: IF bStartCmd THEN eState := STARTING; END_IF; ... END_CASE; Log transitions when state changes.) for clear Safety Systems sequence control
- 2.Constants define Universal-specific parameters: cycle time 30s, batch size
- 3.Input conditioning with debounce timer prevents false triggers in industrial environment
- 4.STARTING state implements soft-start ramp - prevents mechanical shock
- 5.Process timeout detection identifies stuck conditions - critical for reliability
- 6.Safety override section executes regardless of state - Beckhoff best practice for advanced systems
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
- ✓Structured Text: Use meaningful variable names with consistent naming conventions
- ✓Structured Text: Initialize all variables at declaration to prevent undefined behavior
- ✓Structured Text: Use enumerated types for state machines instead of magic numbers
- ✓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
- ⚠Structured Text: Using = instead of := for assignment (= is comparison)
- ⚠Structured Text: Forgetting semicolons at end of statements
- ⚠Structured Text: Integer division truncation - use REAL for decimal results
- ⚠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 Structured Text programs unmaintainable over time