Intrinsic Safety Entity Parameter Calculator
Verify a simple intrinsically safe loop with one associated apparatus and one field device using the entity concept, including cable parameters.
- Total C = Ci + cable = 65 nF, total L = Li + cable = 0.31 mH
- Max length = min((Co − Ci) ÷ c, (Lo − Li) ÷ l) = 390 m
Entity parameter check
| Condition | Barrier or loop | Device limit | Result |
|---|---|---|---|
| Uo ≤ Ui | 28 V | 30 V | OK |
| Io ≤ Ii | 93 mA | 100 mA | OK |
| Po ≤ Pi | 0.65 W | 0.75 W | OK |
| Ci + Ccable ≤ Co | 65 nF | 83 nF | OK |
| Li + Lcable ≤ Lo | 0.31 mH | 4.2 mH | OK |
Entity Concept Conditions
Ci + Ccable ≤ Co, Li + Lcable ≤ Lo
When cable data is unknown, IEC 60079-14 allows 200 pF/m and 1 µH/m to be assumed. Values here are typical of a 28 V, 93 mA zener barrier for gas group IIC.
Worked example
With 300 m of cable at 200 pF/m and 1 µH/m, total C = 65 nF (below 83 nF) and L = 0.31 mH (below 4.2 mH). The loop passes, with capacitance limiting the cable to about 390 m.
Frequently Asked Questions
What is the entity concept?
A method of matching the output parameters of an associated apparatus (barrier) with the input parameters of a field device plus cable, so the combination stays intrinsically safe.
What cable parameters should I use?
Use the manufacturer’s data; otherwise IEC 60079-14 allows 200 pF/m and 1 µH/m.
Do I still need a loop drawing?
Yes. The descriptive system document or loop drawing must record the check and the certificates used.
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