What is the tracking index test apparatus?

The Tracking Index Tester is a specialized instrument used to evaluate the resistance of solid insulating materials to surface leakage and tracking under specific conditions. It is widely applied in the electrical, electronics, household appliances, wires and cables, and printed circuit board industries to ensure the electrical safety of materials in humid or contaminated environments.

Working Principle

The Tracking Index Tester simulates the actual usage conditions of solid insulating materials under the combined effects of an electric field and contamination, assessing their ability to resist surface leakage and tracking (formation of conductive paths). The core measurement focuses on two key indices:

CTI (Comparative Tracking Index): The maximum voltage the material can withstand without forming leakage tracks.

PTI (Proof Tracking Index): The verified voltage at which the material does not form leakage tracks.

Operating Principle Steps:

Sample Placement:

Place the insulating material between two platinum electrodes, with an electrode spacing of 4.0 mm ± 0.01 mm, angle of 60° ± 5°, and electrode pressure of 1.00 N ± 0.001 N.

Voltage Application:

Apply an AC voltage ranging from 100 V to 600 V (continuously adjustable) at a frequency of 48–62 Hz.

Contaminant Dripping:

Drop a 0.1% NH₄Cl solution onto the sample surface from a fixed height (usually 35 mm ± 5 mm) at fixed intervals (30 s ± 0.1 s). The solution’s resistivity must meet standard requirements.

Tracking Monitoring:

When the material surface deteriorates due to the combined effect of the electric field and contaminant, forming a permanent conductive path (tracking), the current rises sharply. If the current ≥0.5 A and lasts ≥2 s, the instrument automatically determines “failure,” cuts off power, and issues an alarm.

Index Determination:

By gradually increasing the voltage and performing multiple tests, record the highest voltage at which no tracking occurs. This is the CTI or PTI value.

Basic Operating Steps

Sample Preparation:

Cut materials to standard dimensions (e.g., 30 mm × 30 mm).

Clean the surface with anhydrous ethanol or distilled water to remove dust, grease, or fingerprints.

Precondition the sample in (23 ± 2) °C and (50 ± 10)% RH for 30 minutes before testing, per GB/T 4207-2022.

Contaminant Solution Preparation:

Class A: 0.1% NH₄Cl solution, resistivity 3.95 ± 0.05 Ω·m.

Class B/C: For more stringent tests, with different resistivity or surfactants.

Verify conductivity before each test.

Equipment Setup:

Install platinum electrodes (2 mm × 5 mm, 60° ± 5°, 4.0 mm ± 0.01 mm spacing).

Set electrode pressure to 1.00 ± 0.001 N.

Set drip height to 35 ± 5 mm, interval 30 ± 0.1 s.

Configure test voltage (100 V, 175 V, 250 V, etc., in 25 V increments).

Test Execution:

Place the sample between electrodes and start the dripping and voltage program.

Observe for tracking (conductive path, continuous arc, or burning).

Failure occurs automatically if current ≥0.5 A for 2.00 s ± 10%.

Result Determination:

PTI: Voltage at which the sample withstands 50 drops without tracking or ignition.

CTI: Highest voltage the sample withstands 50 drops without failure.

Reports include test voltage, number of drops, failure status, and test conditions.

Key Safety & Notes:

Conduct tests in fume hoods or enclosed chambers; wear protective gear.

Calibrate annually (voltage, current, drip timing, electrode pressure).

Test environment: wind speed ≤0.2 m/s, temperature 0–40 °C, humidity ≤80%.

Maintenance Guidelines

Cleaning:

Wipe exterior with a soft damp cloth; avoid liquid ingress.

Clean glass platforms, electrodes, and chambers regularly.

Electrode Care:

Platinum electrodes (≥99% purity) should be inspected for contamination or deformation.

Clean with soft cloth or specialized tools; chemical or mechanical polishing may be applied.

Connections & Components:

Check power and signal cables for wear or looseness.

Ensure drip systems (peristaltic pump or pipette) are unobstructed.

Calibration & Verification:

Verify accuracy using reference samples with known CTI values.

Annual professional calibration per ISO 17025 or manufacturer guidelines.

Environment Management:

Place equipment in dry, temperature-stable, non-corrosive environments.

Avoid direct sunlight and high humidity; cover with dust-proof cover when not in use.

Core Functions and Benefits

Core Functions:

Measure PTI and CTI to evaluate material safety and reliability.

Assess insulating material tracking resistance under humid/contaminated conditions.

Support material selection and quality control.

Comply with IEC 60112. GB/T 4207. UL 746A, ASTM D3638. and other standards.

Guide electrical design parameters (creepage distance, clearance) to prevent short circuits or fire.

Key Benefits:

Enhance product safety by identifying weak materials.

Improve R&D efficiency with quantitative performance data.

Ensure regulatory and market compliance for global certifications.

Modern devices feature digital control, automated dripping, overcurrent protection, and safety interlocks for repeatable and safe testing.

Future Trends

The Tracking Index Tester is rapidly evolving toward intelligent, high-precision, and green designs:

Intelligent: AI algorithms for automatic tracking recognition and lifespan prediction; PLC, touchscreen, and remote maintenance improve usability.

High Precision: New standards demand tighter tolerances on voltage, drip rate, and electrode spacing; stable power supplies, precision pumps, and sensors ensure repeatability.

Green: Machine efficiency >82%, standby power <15 W; modular design and >91% recyclability enhance sustainability.

Application Expansion: Rapid growth in new energy and high-voltage DC (HVDC) equipment; multi-standard compatibility meets export certification needs.