Technical Note: Speed Sensors in PDK Transmissions

Technical Note: Speed Sensors in PDK Transmissions

    The sensing surface of the OEM speed sensor is made from a plastic material known as PEEK (polyether ether ketone). Over time, this material can deform; however, this has minimal impact on performance. The primary issue is that it becomes more brittle with age, and the component itself is relatively expensive.

    Many aftermarket speed sensors on the market use aluminum alloy as the sensing surface. However, a critical factor is often overlooked: the use of aluminum introduces eddy current effects. 

    Eddy currents can significantly affect the rotational speed signal, particularly at high RPM. Based on calculations:

•  At 6000 RPM:

   A 0.2 mm aluminum sensing surface results in approximately 10% signal attenuation and about 20° phase lag.

   A 0.3 mm aluminum sensing surface results in approximately 20% signal attenuation and about 26° phase lag.

•  At 8000 RPM, the impact becomes even more pronounced.
•  At 1000 RPM, the effect is negligible.

    To the best of my knowledge, some brands use aluminum alloy sensing surfaces. While they perform adequately under normal driving conditions, they are not recommended for track use, as higher RPM leads to increased signal instability.

    Some manufacturers use stainless steel for the sensing surface, which eliminates eddy current effects. However, CNC machining costs for stainless steel are roughly three times higher than aluminum. A potential solution could be a hybrid design—using an aluminum alloy body with CNC machining, combined with a stainless steel sensing surface.

Recommendation:

    When selecting a PDK transmission speed sensor, it is essential to verify the material of the sensing surface to avoid potential performance issues.