DUT (Device Under Test) presence detection is a critical safety and operational feature in test fixtures. The system ensures proper device loading before testing commences, protecting both equipment and the device from damage caused by running tests without a board in place.
How It Works#
Switching probes operate as normally-open electromechanical switches that close when contact is made with the device. The plunger can activate beyond the switching point while maintaining electrical connection, accommodating board thickness variations.
Probe Types#
KG-300K Series (Development)#
Development-grade solution featuring:
- Press-fit installation into the probe plate
- Direct solder tab connections
- Low-cost option for prototyping
- Requires desoldering for replacement
Best for development fixtures where cycle count is low and probe replacement is infrequent.
SKS-215 MF Series (Ingun)#
Professional-grade screw-in design offering:
- Adjustable height for precise switching point
- Dual solder connection points
- Tool-free replacement capability
- Higher cycle life rating
Recommended for production fixtures where maintenance efficiency matters.
Integration with Test Point Carrier Boards#
When using TPCBs, presence detection requires specific design considerations:
Footprint Design#
- Use dual-pad footprint (main and secondary pads)
- Main pad connects to probe contact point
- Secondary pad provides signal routing to connector
Circuit Configuration#
- Implement pull-up resistor configuration
- Use normally-open switch logic (active-low detection)
- Connect to a GPIO input on test instrumentation
Layout Guidelines#
- Maintain ground plane clearance around probe pads
- Position vias outside the probe contact area
- Route traces away from the direct probe zone
Maintenance and Troubleshooting#
Common Issues#
| Symptom | Likely Cause | Solution |
|---|---|---|
| False positives | Mechanical binding | Check probe travel, clean mechanism |
| False negatives | Height misalignment | Adjust probe or switching height |
| Intermittent detection | Loose connections | Inspect solder joints, resolder if needed |
Maintenance Schedule#
| Interval | Action |
|---|---|
| Daily | Visual inspection of probe condition |
| Weekly | Verify switching operation |
| Monthly | Check solder connections |
| Quarterly | Replace probes as needed |
Best Practices#
- Position probes strategically — Place presence switches where the board is guaranteed to make contact (typically opposite corners)
- Use multiple switches — Two or more switches provide redundancy and confirm board is flat
- Test the detection system — Verify the presence circuit works before running production tests
- Monitor for wear — Track false detection rates as an early indicator of probe wear
Related Documentation#
- Fixture Switches — Fixture closure detection
- TPCB Guide — Test Point Carrier Board design
- Selecting Probes — Probe selection guidelines