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If I am using an inductive proximity sensors as a safety gate latch, what codes and standards do I need to abide by?

Some safety sensors I research have: - Category 3 (EN ISO 13849) - Safety integrity level (SIL2, SILCL2) - EN ISO 14119

How do I figure out for a given application, what safety integrity level, category, performance level..etc I require for my application?

Edit: We are trying to follow NFPA70, 33, and CSA

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  • \$\begingroup\$ A safety gate on what? \$\endgroup\$ – K H Apr 18 at 4:18
  • \$\begingroup\$ It will be mounted to a door that enters the work area, when the metal door opens the inductive proximity sensor will trigger. \$\endgroup\$ – namtrop Apr 18 at 4:56
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If I am using an inductive proximity sensors as a safety gate latch ...

... when the metal door opens the inductive proximity sensor will trigger.

I'm concerned that you may not understand the potential failure modes.

Safety integrity level (SIL) is defined as a relative level of risk-reduction provided by a safety function, or to specify a target level of risk reduction. In simple terms, SIL is a measurement of performance required for a safety instrumented function (SIF). Source: Safety integrity level.

You need to perform a risk analysis based on

  • Severity of possible injury.
  • Frequency of exposure.
  • Likelihood of avoidance.

That will determine the SIL required.

In general, an inductive proximity switch would not be suitable. You can't predict its failure mode - open-circuit or short-circuit and therefore you can't guarantee that it will switch off the hazard when "triggered" - whatever that means.

Instead, the SIL will require that the switch output turns off when the guard is opened - either by forced disconnection of the switch contacts or by some other means. If there is a risk of permanent or "non-reversible" injury or death the system will require redundant or dual-channel safety with a safety controller that will guarantee that a fault on one channel is detected and will not reset until the fault is cleared.

Your question and comments suggest that you are going to use a prox switch to detect opening of the gate. Instead your safety must prove that the safety gate is closed before energising the circuit.

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  • \$\begingroup\$ Thanks for the response! \$\endgroup\$ – namtrop Apr 19 at 6:31
  • \$\begingroup\$ Thanks for the response! By "triggered" I was referring to a rising edge. The proximity sensor is a N.O switch, meaning when the gate is detected by the switch the circuit will close, indicating to the safety relays that we are in a safe state. This will also be fail-safe in the event of power loss. However, my question was in regards to the codes and standards and I think you gave me a place to start. I was more looking for a required working range of inductive sensors (ie the door can only open <5mm before the door is no longer detected) or respond in < X ms. \$\endgroup\$ – namtrop Apr 19 at 6:38
  • \$\begingroup\$ But what happens when the output transistor fails short-circuit? If you have a part in mind then post a datasheet link. \$\endgroup\$ – Transistor Apr 19 at 6:40

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