Understanding Roughness Tester Values

Profilometers, also known as surface roughness testers, are tools that allow you to test how rough or smooth a given surface is, with varying degrees of accuracy. Most roughness testers will work by moving the unit or a probe across the surface. Features, size, shape, and accuracy vary from device to device. Some can even transit readings to a computer via a Bluetooth or other wireless connection. These devices read out in values such as Ra, Rz, Rt, and more. But what do these roughness values mean, and how do you read the numbers the roughness testers display?

(Pictured: PCE RT 2300 23 Parameter Profilometer Surface Roughness Tester)

More about the readings:

The readings or values provided by roughness testers are unique when compared to other instruments. Roughness can be measured as follows: Rz, Ra, Rt, Rq, Rsm, Rsk, Rp, Rv, and Rc.

Rz = average roughness: The average roughness depth Rz is the arithmetic mean of the largest single-order depths of several adjacent individual measurement sections.

Ra = arithmetic mean roughness:  Ra is the generally recognized and internationally applied roughness parameter. It is the arithmetic mean of the absolute values ​​of the profile deviations within the reference distance. The measured value Ra is always smaller than the Rz value determined on the same roughness profile.

Rt = maximum roughness: The maximum surface roughness Rt is the distance between the highest and the lowest point of the measuring section.

Rq = Square Mean Roughness: Rq is the root mean square of all ordinate values ​​within the individual measurement distance l. Rq corresponds to the designation RMS (Root Mean Square).

RSm = mean peak width: Mean value of the width of the profile elements. Horizontal and vertical counting thresholds are stipulated for this evaluation.

Rsk = Skewness: a measure of the average of the first derivative of the surface (the departure of the surface from symmetry). A negative value of Rsk indicates that the surface is made up of valleys, whereas a surface with a positive skewness is said to contain mainly peaks and asperities.

Rp = Maximum profile peak height: Represents the maximum peak height Zp of a profile within the sampling length.

Rv = Maximum profile valley depth: Represents the maximum peak height Zp of a profile within the sampling length.

Rc = Mean Height: Represents the mean for the height Zt of profile elements within the sampling length.

Now that you know all of the values that your profilometer will read out in, you can start using your device with ease. You can check out all of our profilometers / roughness testers on our site. Feel free to contact us with any questions!