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Question from the Customer:

My company is using the Advanced Cable Tester v2 (Advanced Cable Tester v2) to test a variety of cables, such as USB, HDMI, and DisplayPort cables.

We have a question about our test results for the USB-C to USB-C cables. The DC resistance of the VBUS pins does not pass the test. However, testing the contact resistance of the VBUS pins with other tools, the result is less than 0.04Ω, which meets the specifications. Here is a picture of the test results from the Advanced Cable Tester v2:

The test tables show the following information after the Advanced Cable Tester v2 tests the DC resistance of a pin. This table is for A4:

• Sources,
• Plug1:A4
• Sinks,
• Plug1:B4,B9,A4 Plug2:B4,A9,B9,A4

Here are my questions:

• How do you test the DC resistance of the Plug 1 Pin A4?
• Do you put the positive pole to the Plug1:A4, and put the negative pole to the Plug1:B4,B9,A4 &Plug2:B4,A9,B9,A4, and then test the DC resistance between the two poles?

Here is a diagram of how I think the tests are run:

I do not yet understand the test results. Can you tell me how the Advanced Cable Tester v2 takes measurements and how results are determined?

Response from Technical Support:

Thanks for your question! Your diagram about DC Test Resistance is close to correct – sensing is also part of the test measurement. A current, about 100mA, is passed through the cable, and the voltage difference is measured at multiple test points. Ohm's Law is then used to calculate the resistance. We will describe how the resistance is measured in the following sections.

Measuring Pin Resistance

The official specifications are for the resistance of the mated connectors. In that case, the measurements are taken directly at the leads coming off the back of the plug (receptacle).

However, after the cable has been manufactured, the paddleboard (a printed circuit board, PCB) is encapsulated in plastic; we cannot take such measurements directly. Instead, we take multiple measurements using the alternate pins as sense pins: test points. This method provides the best accuracy that can be acquired under such conditions.

Where Voltage Measurements Are Applied to Calculate Resistance

Here is a simplified diagram about the sense measurements:

Sense1 is used as one half of the differential voltage measurement. The other points are also measured: Sense2, Sense3, and Sense4. The point with the least voltage difference (the least resistance) is then considered "the measurement" for Pin 4.

The unknown is the location where the sense pins merge with the other VBUS conductor:

• If the VBUS power plane on the paddleboard is large, then this will be negligible.
• If current is always flowing through the used sense pin trace, then the measurement may be several milliohms high.

This is not a full connector test, and every cable is different. We apply best effort, and the results are helpful for locating manufacturing problems. The following sections provide details about our Advanced Cable Tester v2 measurements.

About Resistance Measurement

Measuring the resistance of a cable is comparable to measuring a “black box”. Here are explanations about the measurements that were described above.

Why use the Least Voltage Difference as “the measurement” of a Pin?

We aim for the value that is closest to the resistance between the mated plug pair, excluding any PCB traces. On our side, the sense wire joins the current injection trace within 2mm of the receptacle pin – 2mm is a worst case. On the receptable side, we do not know the topology, but the PCB trace will only increase the measured difference. This makes the lowest measurement the best selection for realistic results.

Why is the impedance of a large VBUS power plane on the paddleboard negligible?

In this case, the impedance can be negligible from the paddleboards of the two receptacles at the ends of the cable. It also indicates that the resistance difference between the common wire and each pin is negligible.

There is a rule-of-thumb for PCB trace resistance: The resistance of a ½ ounce circuit board trace is 1mΩ/square × the number of squares down the length of the trace. This means that across a 10mm x 10mm square, the resistance would be about 1 milliohm. Across a 10mm x 1mm square, the resistance would be about 10 milliohms.

Paddleboards may have 10mm of extra trace to a single pin. However, this design is becoming less common.

If the used sense pin trace always has current flowing and affects the measurements, should the cable be connected to Advanced Cable Tester v2 ground?

Grounding is not necessary. The cable ground and the cable shield are isolated from the chassis ground.

Here are the details about “If the used sense pin trace always has current flowing through it then the measurement may be several milliohms high”.

• If no current is flowing through a trace, then the voltage at the start and end will be identical.
• If current is flowing through a trace, then it creates a voltage gradient along the trace.

Referring to the Interpretation of DC Test Resistance diagram that you provided, and assuming that the cable was built with copper traces as represented by the lines in the schematic, then the path for current is through pin 4, down to the center horizontal wire, and into Plug 2. In this scenario, Sense3 and Sense4 would provide identical voltage measurements.

As previously stated, the actual topology of a paddleboard is unknown, and we apply best effort. The measurement provided by the Advanced Cable Tester v2 can be slightly higher than what you would acquire from a measurement across a bare paddleboard.

Test Profiles and Test Results

Test results may be affected by the version of the cable design, including the E-Marker chip. Profiles can be set up to run tests more accurately. For more information, please refer to this article: What Details are Needed in the Profile to Accurately Run Type-C Cable Tests?

We hope this answers your question. Additional resources that you may find helpful include the following:

• Advanced Cable Tester v2 User Manual
• Advanced Cable Tester v2 Quick Start Guide

Additional information about using the Advanced Cable Tester v2:

• Testing HDMI Cables Using the Advanced Cable Tester v2
• Testing USB, Apple Lightning, and Video Cables with the Advanced Cable Tester v2

If you want more information, feel free to contact us with your questions, or request a demo that applies to your application.

Request a Demo