Safety Considerations Guide for Trident v2 Systems - TUV ...

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66 Appendix A Triconex Peer-to-Peer Communication Table 16 Data Transfer Time Formula Parameters Parameter Description TS Time for sending node to transfer Aliased data over the communication bus in milliseconds = (Number of aliased variables in bytes ÷ 100,000) * 1000 SS Scan time of sending node in milliseconds TR Time for receiving node to transfer Aliased data over the communication bus in milliseconds = (Number of aliased variables in bytes ÷ 100,000) * 1000 SR 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. Safety Considerations Guide for Trident v2 Systems 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. 12. Compare the adjusted DT to the process-tolerance time to determine if it is acceptable. Adjusted DT _________
Data Transfer Time 67 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 69. 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 69. Refer to the TriStation 1131 Libraries Reference for additional information. Safety Considerations Guide for Trident v2 Systems
Page 1 and 2:
Trident v2 Systems Safety Considera
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:
• All other requests are handled
Page 11 and 12:
1 Safety Concepts Overview 2 Hazard
Page 13 and 14:
Protection Layers Methods that prov
Page 15 and 16:
Hazard and Risk Analysis Hazard and
Page 17 and 18:
Sample SIL Calculation Hazard and R
Page 19 and 20:
Safety Life Cycle Model Hazard and
Page 21 and 22:
Hazard and Risk Analysis 11 • Eac
Page 23 and 24:
CAN/CSA-C22.2 No. 61010-1-04 Safety
Page 25 and 26: 2 Application Guidelines Overview 1
Page 27 and 28: General Guidelines This section des
Page 29 and 30: General Guidelines 19 Safety Measur
Page 31 and 32: Emergency Shutdown Systems The safe
Page 33 and 34: Safety-Shutdown Guidelines for Tric
Page 35 and 36: Guidelines for Triconex Controllers
Page 43 and 44: 3 Fault Management Overview 34 Syst
Page 45 and 46: System Diagnostics System Diagnosti
Page 47 and 48: Operating Modes Each input or outpu
Page 49 and 50: Analog Output (AO) Modules Module D
Page 51 and 52: Calculation for Diagnostic Fault Re
Page 53 and 54: External Communication Module Diagn
Page 55 and 56: 4 Application Development Developme
Page 57 and 58: Array Index Errors Infinite Loops D
Page 59 and 60: Setting Scan Time 49 application. T
Page 61 and 62: Sample Safety-Shutdown Programs Sam
Page 63 and 64: Sample Safety-Shutdown Programs 53
Page 65 and 66: When Some I/O Modules Are Safety-Cr
Page 67 and 68: Sample Safety-Shutdown Programs 57
Page 69 and 70: Partitioned Processes Sample Safety
Page 71 and 72: Alarm Usage Alarm Usage 61 To imple
Page 73 and 74: A Triconex Peer-to-Peer Communicati
Page 75: Data Transfer Time Data Transfer Ti
Page 79 and 80: Examples of Peer-to-Peer Applicatio
Page 81 and 82: B HART Communication Overview 72 HA
Page 83 and 84: 2008-04-01 Automation, Software and
Page 85 and 86: 2008-04-01 HART Position Paper from
Page 87 and 88: 2008-04-01 A possible impact to the
Page 89 and 90: 2008-04-01 HART Position Paper from
Page 91 and 92: C Safety-Critical Function Blocks O
Page 93 and 94: SYS_CRITICAL_IO Accumulates the sta
Page 95 and 96: Library Trident and Tri-GP (TRDLIB)
Page 97 and 98: END_IF ; PREVIOUS_RESET := RESET ;
Page 99 and 100: Output Parameters (continued) Name
Page 101 and 102: SYS_SHUTDOWN 91 * the safety system
Page 103 and 104: ALARM_DISABLED_POINTS := MPX.POINTS
Page 105 and 106: Example For shutdown examples, see
Page 107 and 108: A abbreviations, list of viii actua
Page 109 and 110: message errors, external communicat
Page 112: Invensys Operations Management 5601
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