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Safety and SIS · Glossary

What is Intrinsic Safety?

Symbol: Ex ienergy limitationSafety and SIS

Intrinsic safety is a protection method that limits electrical and thermal energy in a circuit so it cannot ignite an explosive atmosphere.

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Intrinsic Safety Explained

Barriers or isolators in the safe area limit voltage, current and power to field devices. Levels ia, ib and ic tolerate two, one and no faults.

Each loop is checked by comparing the entity parameters of the barrier with the field device and cable.

Intrinsic Safety Formula

Uo ≤ Ui, Io ≤ Ii, Po ≤ Pi, Co ≥ Ci + Ccable, Lo ≥ Li + Lcable
obarrier (associated apparatus) outputs
ifield device inputs
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Calculators for Intrinsic Safety

CalculatorIntrinsic Safety CalculatorFree online calculator with formula and worked example.CalculatorLoop Power Supply CalculatorFree online calculator with formula and worked example.

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Frequently Asked Questions

What is Intrinsic Safety?

Intrinsic safety is a protection method that limits electrical and thermal energy in a circuit so it cannot ignite an explosive atmosphere.

Zener barrier or galvanic isolator?

Zener barriers need a high integrity earth; isolators do not and are now more common.

Can IS cables run with other cables?

They must be separated and identified, typically with light blue sheaths, as required by IEC 60079-14.

Related Terms

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More Safety and SIS Terms

Safety termFault Tree AnalysisFault tree analysis is a top down method that models how combinations of basic failures lead to an…Safety termSafety Instrumented SystemA safety instrumented system is an independent set of sensors, logic solver and final elements that takes…Safety termSafety Instrumented FunctionA safety instrumented function is one protective action of a SIS, from sensing a hazard to the final…Safety termSafety Integrity LevelSafety integrity level is a target level of risk reduction for a safety instrumented function, from SIL 1…Safety termPFDavgPFDavg is the average probability that a safety function fails to act when a demand occurs, over the…Safety termPFHPFH is the average frequency of dangerous failures per hour, used for safety functions in high demand or…

All safety and sis terms · Full glossary A to Z

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