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

Calculation for Diagnostic Fault Reporting Time
Module Diagnostics 41
Typical and worst-case fault reporting times can be determined by using the formula in this
section. For typical configurations with less than eight AI modules, the calculation is not
required and the default values can be used. The default values are:
• 500 milliseconds for a typical case
• 725 milliseconds for a worst case
For configurations with more than eight AI modules, the formula allows you to calculate typical
and worst-case fault reporting times. This table provides a sample calculation.
Table 5 Calculating Diagnostic Fault Reporting Time Example
Module
Type
Procedure
Number in
System
Multiplier Result
AI 10 16 160
DI 2 1 2
PI 0 6 0
AO 0 5 0
DO 2 1 2
SRO 0 1 0
164 x 1.2 = 196.8
Typical Case: 196.8 x 3 = 590.4 milliseconds + 1/2 scan time
Worst Case: 196.8 x 4.5 = 885.6 milliseconds + 1 scan time
1 Enter the number of modules and multiply each by the multiplier for the module type
and then add the results.
2 Multiply the result of step 1 by 1.2.
3 If the result for step 2 is greater than 150, use the greater number; otherwise, use 150.
4 To determine the typical case, multiply the result of step 3by 3, and then add 1/2 the
application scan time.
5 To determine the worst case, multiply the result of step 4 by 4.5, and then add 1
application scan time.
Safety Considerations Guide for Trident v2 Systems