Safety Interlock System Integration
The NI 4136/4137 includes a safety interlock circuit that places the outputs of the SMU device
in a safe state, regardless of the programmed state of the device.
• 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 2. System Level Connection, Typical
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2
Safety Interlock Connector
Test Fixture Enclosure
Operator Access Door
Mechanical Detection Switches
Mechanical detection switch is actuated
by operator access point
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4
Related Information
Fore more information about the Safety Interlock, refer to the NI DC Power Supplies and
SMUs Help.
Testing the Safety Interlock on page 10
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.
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