To initiate an intrinsic safety calculation by loop, in the Wiring Module window, on the Associations menu, click Intrinsic Safety Loop Calculation. For details, see Calculate Intrinsic Safety for a Loop. For a summary of the differences between intrinsic safety (IS) calculation by circuit type and by loop, see the following table:
|
Feature |
By Circuit Type |
By Loop |
|
Level |
Circuit type |
For all the tags in a loop |
|
Cables |
One Cable A and one Cable B |
All cables in the circuit for which the IS check box is selected |
|
Parameters Considered |
Resistance |
Resistance |
|
Inductance |
Inductance |
|
|
Capacitance |
Capacitance |
|
|
|
L/R |
|
|
Result |
Maximum permissible length of Cable A |
Pass / fail for all tags associated with an IS circuit type |
|
parameter that limits length |
||
|
Report |
Full diagram with calculation results; |
Instrument & barrier safety characteristics; |
|
Calculation explanation |
List of IS cables and their characteristics; |
|
|
|
If Pass, calculated results, including (L/R) cables |
Assumptions
For each tag in a loop, the intrinsic safety calculation considers the following values:
-
The parameters of the hazardous area field device: Rhaz tag, Lhaz tag, and Chaz tag.
-
The parameters of the safety device in the non-hazardous area: Rsafety, Lsafety, Csafety, and L/Rsafety.
-
Parameters associated with Cablei (i= A, B).
-
R_factCable i, L_factCable i, and C_factCable i, all of which are determined by the cable type.
-
LengthCable i
-
Calculating Cable Parameter Values
For each cable, the software calculates the following values:
Determining Whether a Circuit is Intrinsically Safe
For each tag in the loop, if all the following are true, the software certifies the tag circuit as intrinsically safe:
