Safety Considerations Guide for Triconex General ... - ICEWeb

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64 Appendix A Triconex Peer-to-Peer Communication Table 16 Parameter TS SS TR SR Data Transfer Time Formula Parameters Description Time for sending node to transfer Aliased data over the communication bus in milliseconds = (Number of aliased variables in bytes ÷ 100,000) * 1000 Scan time of sending node in milliseconds Time for receiving node to transfer Aliased data over the communication bus in milliseconds = (Number of aliased variables in bytes ÷ 100,000) * 1000 Scan time of receiving node in milliseconds Procedure 1 Use the instructions in the following worksheet to estimate the transfer time. Steps 1. Enter the number of bytes for each point type on the sending controller and divide or multiply as indicated. Add the results. Point Type Allocated Bytes Operation Result BOOL _________ ÷ 8 = _________ DINT _________ x 4 = _________ REAL _________ x 4 = _________ Total bytes of aliased points TBS = _________ 2. Multiple total bytes sending TBS (step 1) by 0.01 TS = _________ 3. Enter the number of bytes for each point type on the receiving controller and divide or multiply as indicated. Add the results. BOOL _________ ÷ 8 = _________ DINT _________ x 4 = _________ REAL _________ x 4 = _________ Total bytes of aliased points TBR = _________ 4. Multiple total bytes receiving TBR (step 3) by 0.01 TR = _________ 5. Get the scan time of sending node in milliseconds by viewing the Scan Time in the Execution List. 6. Get the scan time of receiving node in milliseconds by viewing the Scan Period in the Execution List. SS = SR = _________ _________ 7. Multiply the larger of TS or SS by 2. _________ 8. Multiply the larger of TR or SR by 2. _________ 9. Add the results of step 7 and 8 to get the data transfer time = DT _________ 10. If the number of pending send requests in the application is greater than 10, divide the number of send requests by 10. 11. Multiply the results of steps 9 and 10 to get the adjusted data transfer time. Adjusted DT 12. Compare the adjusted DT to the process-tolerance time to determine if it is acceptable. _________ _________ Safety Considerations Guide for Triconex General Purpose v2 Systems
Data Transfer Time 65 A typical data transfer time (based on a typical scan time) is 1 to 2 seconds, and the time-out limit for a Peer-to-Peer send (including three retries) is 5 seconds. Consequently, the processtolerance time of the receiving controller must be greater than 5 seconds. Process-tolerance time is the maximum length of time that can elapse before your control algorithms fail to operate correctly. If these limitations are not acceptable, further analysis of your process is required. For an example that shows how to measure the maximum data transfer time and use SEND/RECEIVE function blocks to transfer-safety critical data, see Example 4: Using SEND/RECEIVE Function Blocks for Safety-Critical Data on page 67. While testing your system, you should measure the actual maximum time it takes to transfer data to ensure the validity of your calculations. As Table 16 shows, it takes from two to 30 seconds to detect and report time-out and communication errors. This is why a receiving node that uses the received data to make safetycritical decisions must include logic to verify that new data is received within the specified time period. If the data is not received within the specified process-tolerance time, the application must take appropriate actions depending on requirements. For an example that shows how to use SEND and RECEIVE function blocks for transferring safety critical data, see Example 4: Using SEND/RECEIVE Function Blocks for Safety-Critical Data on page 67. Refer to the TriStation 1131 Libraries Reference for additional information. Safety Considerations Guide for Triconex General Purpose v2 Systems
Page 1 and 2:
Triconex General Purpose v2 Systems
Page 3 and 4:
Contents Preface vii Summary of Sec
Page 5 and 6:
Contents v Partitioned Processes. .
Page 7 and 8:
Preface This guide provides informa
Page 9 and 10:
Preface ix • All other requests a
Page 11 and 12:
1 Safety Concepts Overview 2 Hazard
Page 13 and 14:
Overview 3 Protection Layers Method
Page 15 and 16:
Hazard and Risk Analysis 5 Hazard a
Page 17 and 18:
Hazard and Risk Analysis 7 Sample S
Page 19 and 20:
Hazard and Risk Analysis 9 Safety L
Page 21 and 22:
Hazard and Risk Analysis 11 • Eac
Page 23 and 24: Safety Standards 13 CAN/CSA-C22.2 N
Page 25 and 26: 2 Application Guidelines Overview 1
Page 27 and 28: General Guidelines 17 General Guide
Page 29 and 30: Guidelines for Triconex Controllers
Page 41 and 42: 3 Fault Management Overview 32 Syst
Page 43 and 44: System Diagnostics 33 System Diagno
Page 45 and 46: Operating Modes 35 Operating Modes
Page 47 and 48: Module Diagnostics 37 Analog Output
Page 49 and 50: Module Diagnostics 39 Calculation f
Page 51 and 52: Module Diagnostics 41 External Comm
Page 53 and 54: 4 Application Development Developme
Page 55 and 56: Development Guidelines 45 Array Ind
Page 57 and 58: Setting Scan Time 47 application. T
Page 59 and 60: Sample Safety-Shutdown Programs 49
Page 69 and 70: Alarm Usage 59 Alarm Usage To imple
Page 71 and 72: A Triconex Peer-to-Peer Communicati
Page 73: Data Transfer Time 63 Data Transfer
Page 77 and 78: Examples of Peer-to-Peer Applicatio
Page 79 and 80: B HART Communication Overview 70 HA
Page 81 and 82: HART Position Paper from TÜV Rhein
Page 89 and 90: C Safety-Critical Function Blocks O
Page 91 and 92: SYS_CRITICAL_IO 81 SYS_CRITICAL_IO
Page 93 and 94: SYS_CRITICAL_IO 83 Library Trident
Page 95 and 96: SYS_CRITICAL_IO 85 END_IF ; PREVIOU
Page 97 and 98: SYS_SHUTDOWN 87 Output Parameters (
Page 99 and 100: SYS_SHUTDOWN 89 * the safety system
Page 101 and 102: SYS_SHUTDOWN 91 ALARM_DISABLED_POIN
Page 103 and 104: SYS_VOTE_MODE 93 Example For shutdo
Page 105 and 106: Index A abbreviations, list of viii
Page 107 and 108: Index 97 N NFPA 85 12 O operating m
Page 110: Invensys Operations Management 5601
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