The Proof Tracking Index (PTI) and the Comparative Tracking Index (CTI) are both methods used to evaluate the electrical tracking resistance of insulating materials. Here are the key differences between the two:
1. Test Methodology:
- PTI: The PTI test, as per IEC 60112 standard, involves applying a voltage to a set of electrodes on the material surface and subjecting it to a conducting contaminant solution. The test assesses the time taken for the material to form a conducting path between the electrodes.
- CTI: The CTI test, as per ASTM D3638 standard, follows a similar methodology. It applies a voltage and conducting contaminant solution to the material surface and evaluates the time taken for the material to form a conducting path.
2. Test Conditions:
- PTI: The PTI test is typically performed with a fixed voltage of 600V (alternating current) and sodium chloride as the conducting solution.
- CTI: The CTI test can be performed with different fixed voltages depending on the standard being used (e.g., 600V, 1000V, or 1500V) and typically involves using a conducting solution containing sodium chloride.
3. Reporting Units:
- PTI: PTI values are reported in seconds (time taken to form a conducting path).
- CTI: CTI values are reported as voltage levels (e.g., CTI 100, CTI 175), representing the voltage at which 50% of the test specimens would fail within a specified time frame.
4. Standards:
- PTI: The PTI test method is primarily defined by the IEC 60112 standard.
- CTI: The CTI test method is primarily defined by the ASTM D3638 standard.
While the PTI and CTI tests have some differences in terms of test conditions and reporting units, they both provide valuable information about the tracking resistance of insulating materials. Manufacturers and users can utilize these indices to assess and compare the electrical performance of materials for specific applications.