Testing intrinsic-safety barriers with an electronic load & DMM
Verify that IS fusing and protection circuitry stays below its temperature limits: sink the maximum rated power with an SDL1000X in Constant Power mode and scan up to 12 thermocouples.
Intrinsic safety (IS) protects equipment in hazardous areas by limiting the electrical and thermal energy available for ignition. IS designs use special fusing and dissipating elements that must never exceed their temperature rating — even during a fault. Verifying that is a power-and-temperature test, and an electronic load makes it repeatable.
The test in one sentence
Load the circuit to its maximum rated power, wait the specified soak time, and measure the temperature of every element that dissipates — heatsinks, packages, resistors, traces. A power-resistor network works, but an SDL1000X electronic load (200/300 W) is far more convenient: Constant Power mode holds the exact wattage regardless of voltage drift, with CR/CV modes and user-defined limits for safe operation.
Step by step
- Connect the device under test to the load's input terminals
- Select Constant Power (CP) mode
- Set the current and voltage ranges (I_range / V_range) for the test
- Set the power the load should sink and activate the input
- After the soak time required by your standard, measure component temperatures
Multi-point temperature logging
Use a thermal camera for a quick overview, or thermocouples with a bench multimeter for documented numbers. The SDM3055-SC and SDM3065X-SC multimeters take the SC1016 scanner card, which scans up to 12 thermocouples — heatsink, fuse, barrier resistors and PCB hot spots — and logs them in one sweep.
The SC1016 is a multiplexer, not twelve parallel meters: it switches the single DMM input between channels and measures them one after another. Siglent specifies two scan speeds, fast at 50 readings/s and slow at 5 readings/s, so a 12-channel sweep takes roughly a quarter of a second at best. That is comfortably fast for thermal work, where temperatures move over seconds and minutes — but do not use it to catch a fast transient on twelve points at once, and remember that channel 12 is sampled slightly later than channel 1.
Leave as much of the original design in place as possible — shielding, case and metalwork all change the thermal picture. An open board measures optimistic.
Result: a documented worst-case temperature profile at rated fault power — exactly the evidence an IS assessment asks for.
Instruments used in this note
200/300 W, CP/CR/CV/CC modes
12-channel thermocouple scanning with -SC models
Related application notes
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