Safety Considerations Guide for Triconex General ... - ICEWeb
Safety Considerations Guide for Triconex General ... - ICEWeb
Safety Considerations Guide for Triconex General ... - ICEWeb
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Data Transfer Time 65<br />
A typical data transfer time (based on a typical scan time) is 1 to 2 seconds, and the time-out<br />
limit <strong>for</strong> a Peer-to-Peer send (including three retries) is 5 seconds. Consequently, the processtolerance<br />
time of the receiving controller must be greater than 5 seconds. Process-tolerance time<br />
is the maximum length of time that can elapse be<strong>for</strong>e your control algorithms fail to operate<br />
correctly. If these limitations are not acceptable, further analysis of your process is required.<br />
For an example that shows how to measure the maximum data transfer time and use<br />
SEND/RECEIVE function blocks to transfer-safety critical data, see Example 4: Using<br />
SEND/RECEIVE Function Blocks <strong>for</strong> <strong>Safety</strong>-Critical Data on page 67. While testing your<br />
system, you should measure the actual maximum time it takes to transfer data to ensure the<br />
validity of your calculations.<br />
As Table 16 shows, it takes from two to 30 seconds to detect and report time-out and<br />
communication errors. This is why a receiving node that uses the received data to make safetycritical<br />
decisions must include logic to verify that new data is received within the specified time<br />
period. If the data is not received within the specified process-tolerance time, the application<br />
must take appropriate actions depending on requirements.<br />
For an example that shows how to use SEND and RECEIVE function blocks <strong>for</strong> transferring<br />
safety critical data, see Example 4: Using SEND/RECEIVE Function Blocks <strong>for</strong> <strong>Safety</strong>-Critical<br />
Data on page 67.<br />
Refer to the TriStation 1131 Libraries Reference <strong>for</strong> additional in<strong>for</strong>mation.<br />
<strong>Safety</strong> <strong>Considerations</strong> <strong>Guide</strong> <strong>for</strong> <strong>Triconex</strong> <strong>General</strong> Purpose v2 Systems