High Voltage Compatible Test Fixtures

What is Considered a High-Voltage Application?

There are testing scenarios where precautions must be taken in designing a bed of nails test fixture regarding the operator's safety and protection from dangerous voltages. In such scenarios, mechanisms must be in place to physically lock the test fixture for the test duration and ensure that the test cannot start until the fixture lid has been closed and locked.

Generally, the safety of machinery is defined in international specifications IEC 60204-1 and IEC 61010-1.

• System power supply voltages > 60V
• Hipot insulation testing (~50V to ~5KV)

FixturFab uses two primary test fixture accessories when high-voltage protection is required: an interlock device and a grounding kit.

A Note on Hipot Testing

Hipot testing, short for high potential testing (also called dielectric strength test), is an electrical safety test designed to verify the insulation of circuit boards, cables, or other wired assemblies. These tests check for good isolation.

In addition to test fixtures for functional testing that require high voltages, FixturFab can design hipot enclosures for PCBs. Both types of test fixtures will integrate the accessories covered in the following sections.

Interlock Devices

An interlock is a safety mechanism designed to prevent accidents or unauthorized access by ensuring that certain conditions are met before the test system can operate. In the context of test system engineering, interlocks are commonly used to control the sequence of operations or to prevent unsafe conditions.

Hipot testers always support an interlock interface to ensure dangerous voltages are NOT applied to the test system if the test fixture is open.

• The test fixture can only be opened when the system is connected to a power supply. A triangular key is provided to unlock the fixture for maintenance access manually.
• In the event of power loss, the overall status of the Test System is unknown, so the test fixture remains locked until power and system functionality is returned to a known state.

To implement this, FixturFab installs two accessories that are supported in production test fixtures.

• An Ingun safety switch (FB-SIS-ZSG-MA) is a solenoid interlock that prevents the lid from opening.
• An Ingun inductive switch (FB-ABF-V-I-MA2xxx) ensures the lid is closed before starting the test.

These accessories are added to any test fixture applying supply voltages > 60V.

Integrating a Solenoid Interlock

The internal schematic diagram for the interlock solenoid is shown in the following illustration. Various relay contact points change position based on the state of the actuator’s engagement with the solenoid. These circuits are used to implement the interlock function for high-voltage test fixtures.

Grounding Kits

When high voltages are involved, there's a significant risk of electric shock. A grounding kit safely directs any excess electrical current away from the operator and the tested equipment to the earth. This reduces the risk of electric shock in case of insulation failure or other faults. It does this by ensuring that all metal surfaces on the fixture that the operator can touch are in contact with the earth's ground.

Again, an Ingun inductive switch is used with a grounding kit to ensure the fixture is closed prior to test commencement.

• An Ingun grounding kit (FB-SLV-MAxx11) ensures all metal features are securely connected to earth ground.
• FixturFab can install these into any production test fixture.

Other Benefits of Adding a Grounding Kit

In addition to protecting the test fixture, operator grounding kits provide several other benefits.

• Protection of Equipment: Grounding protects not only the operator but also the test system from potential damage. In the event of a fault or insulation failure, the grounding kit helps to dissipate the excess voltage and current, thus preventing damage to both the test equipment and the device under test.
• Compliance with Standards: Many electrical safety standards require proper grounding for testing equipment. Not adhering to these standards can lead to legal and regulatory issues, especially in industries that are highly regulated for safety.
• Accurate Test Results: Grounding helps stabilize the test environment, which can lead to more accurate test results. If the test fixture isn't properly grounded, the floating potential can cause inconsistent and unreliable test outcomes. Therefore, they’re typically installed if the Device Under Test (DUT) is particularly ESD-sensitive.
• Noise Reduction: Proper grounding can reduce electrical noise in the test results. Electrical noise can interfere with the accuracy of the Hipot test, leading to false positives or negatives.

Conclusion

Designing high-voltage compatible test fixtures involves integrating interlocks and grounding kits. These accessories are required to adhere to international safety standards like IEC 60204-1 and IEC 61010-1.

The additional features not only safeguard operators from electric shocks but also protect the equipment from potential damage, ensuring that testing processes are both safe and reliable. As electrical test systems become increasingly complex, such advancements in safety and testing are essential for reliable and repeatable test results.