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PXIe-4135 Safety Interlock System Integration

Last Modified: November 23, 2020

The PXIe-4135 includes a safety interlock circuit that places the outputs of the SMU in a safe state, regardless of the programmed state of the module.

  • Do not short the safety interlock pins directly at the connector under any circumstances.
  • Confirm on a regular basis that the safety interlock is functioning by performing a safety interlock test.
  • Install mechanical detection switches that open the safety interlock circuit when the operator attempts to access the test fixture, disabling the hazardous voltage ranges of the instrument.
  • Ensure the mechanical detection switches close the safety interlock circuit only when the operator has properly closed all entry points to the test fixture enclosure, enabling hazardous voltage ranges on the instrument.
Figure 1. System Level Connection, Typical
  1. Safety Interlock Input
  2. Safety Interlock Ground
  3. Safety Interlock Pass Thru - Input
  4. Safety Interlock Pass Thru - Ground

Mechanical Detection Switch Recommendations

  • Use high-reliability, fail-safe, normally open mechanical detection switches on all access points to the test fixture enclosure.
  • Use two normally open switches wired in series so that a single switch failure does not compromise safety protections.
  • Isolate switches so the operator cannot trigger or bypass the switches without the use of a tool.
  • Ensure the switches' certifications meet your test application requirements. NI recommends UL-certified safety switches to ensure reliability.
  • Install the switches in accordance with the switch manufacturer specifications.
  • Test the switches periodically to ensure proper implementation and reliability.

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