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