Fixture Switches for Frame Closed Detection
Overview
A fixture switch detects when the pressure frame is closed on a test fixture, confirming the DUT (Device Under Test) is properly seated and test probes are making adequate contact before testing begins. The type of switch varies by fixture platform and application — balancing cost, cycle life, reliability, and safety requirements.
Switch Types
End-Stop Switch (Dev / Dev Pro)
Mechanical limit switch actuated when the pressure frame reaches end of travel. Provides both NO and NC contacts on a single switch.
- Dual contact configuration (NO + NC)
- Cost-effective for development and low-volume testing
- Easy to install and troubleshoot
Pinout (3-Pin)
| Pin | Label | Function |
|---|---|---|
| 1 | S | Common connection |
| 2 | G | Normally Open (NO) contact |
| 3 | V | Normally Closed (NC) contact |
Connector & Cable (Dev Pro)
End-stop switch PCB with JST XHP-3 connector
- Connector: JST XHP-3 (3-position housing)
- Cable: 18" long, JST XHP-3 on both ends
- Location: End-stop PCB in rear corner of base
- Included with Dev and Dev Pro fixture purchase.
Probe Switch
Two test probes on the probe plate + a conductive shorting plate on the pressure plate. When closed, the plate bridges both probes, creating a detectable short.
- Very low cost — uses standard probes + metal plate
- No additional mechanical switches required
Stroke Switch
Higher cycle life than end-stop, designed for production. Available with various actuation forces, NO and NC contacts.
Inductive Switch
Contactless electromagnetic detection of a metal target. No mechanical wear — ideal for high-cycle production (1M+ cycles).
Safety Switch
Interlocking mechanisms prevent accidental fixture opening during test. Can integrate with e-stop systems. NO and NC configurations.
Contact Configuration
Normally Open (NO) — Simple Detection
Contacts open when fixture is open, closed when fixture is closed. Intuitive for simple presence detection.
Normally Closed (NC) — Fail-Safe
Contacts closed when fixture is open, open when fixture is closed. A broken wire or failed switch prevents testing.
Ingun Functional Units
| Part Number | Type | Description |
|---|---|---|
| FB-SIS-ZSO-MA | Safety | Safety switch w/ solenoid interlock NO |
| FB-SIS-ZSG-MA | Safety | Safety switch w/ solenoid interlock NC |
| FB-SIS-MA | Safety | Safety switch w/o solenoid interlock |
| FB-SIS-BM-MA | Safety | Magnetic safety switch |
| FB-ABF-G-S-MA | Stroke | Closed frame check, stroke switch |
| FB-ABF-K-I-MA | Inductive | Closed frame check, inductive sensor |
| FB-ABF-V-I-MA | Inductive | Locking position, inductive sensor |
| FB-ABF-V-SKS-MA | Probe | Locked kit check, switching probe |
Switch Comparison
| Feature | End-Stop | Probe | Stroke | Inductive | Safety |
|---|---|---|---|---|---|
| Use Case | Dev / Dev Pro | Any fixture | Production | High-volume | Safety-critical |
| Contacts | NO + NC | NO (short) | NO / NC | Digital output | NO / NC |
| Cycle Life | Moderate | Probe-limited | High | 1M+ cycles | High |
| Mech. Wear | Yes | Yes (probes) | Yes | None | Low |
| Cost | Low | Very Low | Medium | Higher | Higher |
| Interlock | No | No | No | No | Yes |
Example Circuits
End-Stop / Stroke — NO Contact Reading
- Frame open → switch open → GPIO reads LOW
- Frame closed → switch closed → GPIO reads HIGH
End-Stop — NC Contact (Fail-Safe)
- Frame open → switch closed → GPIO reads LOW
- Frame closed → switch opens → GPIO reads HIGH
- Wire break → GPIO HIGH → test blocked
Probe Switch — Shorting Plate
- Frame open → probes isolated → GPIO reads HIGH
- Frame closed → plate bridges → GPIO reads LOW
Inductive — NPN Output (Typical)
- No target → output HIGH (open collector off)
- Target near → output LOW (NPN sinks to GND)
Best Practices
- Debounce: Software debounce on mechanical switch inputs
- NC for safety: Use NC contacts for safety-critical apps
- Inductive for volume: >100k cycle production fixtures
- Redundancy: Dual switches for critical apps
- Maintenance: Include switch inspection in fixture validation