California Profilograph in the Field (Click to Zoom)
The California Profilograph is a device used to measure the surface roughness of new or rehabilitated pavement. The profilograph has been used in roughness testing for over 70 years. Surface roughness can be quantified through analysis using roughness indexes. Especially notable for this device is the Profilograph Index (PI). A “California” profilograph is one that meets certain requirements for wheel configuration and frame geometry. These characteristics are standardized because they affect the profiling results.
A California Profilograph consists of a metal truss supported by wheel trucks on each end. The truss provides increased stability over the large span compared to a beam design. The single wheel mounted in the center is part of the deflection measuring system. This system measures the change in vertical height of the center wheel in relation to the support wheels either mechanically or electronically. Compared to recording the pavement directly, recording a wheel’s response naturally smooths the profile. The device is controlled with a side-mounted steering wheel, and is pushed by hand or powered by a motor. Testing is done at low speeds to ensure accuracy.
Older profilographs use a mechanical data recording system, while modern profilographs use an electronic system. A mechanical data recording setup uses a cable to connect the recording wheel to a revolving drum. Moving the profilograph causes the drum to rotate while a static writing implement draws a continuous line on a roll of paper wrapped around the drum. With this method, the PI is calculated manually by counting the number of drawn bumps that exceed minimum height and length requirements, then dividing by the distance traveled. An electronic setup measures the vertical change of the recording wheel with a laser and saves data to an on-board computer. The PI is calculated by the computer with user-set minimums.
Performing Profilograph Field Testing (Click to Zoom)
The California Profilograph is highly well-known and often used as a baseline pavement roughness measurement. An advantage of the profilograph is its truly continuous profile line. It is best used for field longitudinal tests. Among the roughness testing devices, the California Profilograph produces unique results that may not be comparable to others.
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