Profilometer Uses

Background
A stylus / surface contact profilometer uses a diamond tip which transverses on a surface with very light pressure to transfer information about surface topography. The movement of the tip actuates a extremely sensitive transducer LVDT (Linear Variable Differential Transducer) that converts movement in electrical signal. This stylus type surface profilometer allows measuring a complete range of surface roughness characteristics. The stylus is commonly interchanged with the descriptors: tip, probe, detector, pick up and thingee. The term detector, pick up and probe are most commonly used term to describe the unit that houses the LVDT and the actual stylus of the profilometer. The stylus, tip and needle are the terms used to describe the actual diamond point on the profilometer that is similar to a needle on a record turntable. A thingee is a term that people use when they don't know the correct name for something.

The tip of the profilometer is typically a conical diamond and has a finite rounded shape, which interacts with the surface being measured. A profilometer stylus is moved vertically in contact with a sample and then moved laterally across the sample for a specified distance and specified contact force. A profilometer detector can measure small surface variations in vertical stylus displacement as a function of position. Typically, a profilometer can measure small vertical features ranging in height from 10 nanometres to 1 millimetre. The height position of the diamond stylus generates an analog signal which is converted into a digital signal stored, analyzed and displayed.

The radius of diamond stylus ranges from 20 nanometres to 50 μm, and the horizontal resolution is controlled by the scan speed and data signal sampling rate. The stylus tracking force can range from less than 1 to 50 milligrams. The vertical sensitivity is in the nanometer range but steep edge profiles are distorted because of the shape of the tip (see image below). As a result, smaller radius tips provide better measurements however they are more likely to be damaged by mishandling.

The accuracy of a profilometer scan can only be as good as the mechanical stability of the detector/probe and stylus. The profilometer tip can be subject to damage by shear forces-- not normal forces, as a result of misuse on the shop floor. Normal stylus tip force is regulated by the instrument however very large shear forces can be applied to the stylus if the sample stage is inappropriately adjusted with the stylus in contact with the surface, or is bumped while in a prone position.

Advantages of Contact Profilometers

Acceptance: Most of the world's surface finish standards are written for contact profilometers. To follow the prescribed methodology, this type of Profilometer is often required.

Surface Independence: Contacting the surface is often an advantage in dirty environments where non-contact methods can end up measuring surface contaminants instead of the surface itself. However, because the stylus is in contact with the surface, this method is not sensitive to surface reflectance or color.

Resolution: The stylus tip radius can be as small as 20 nanometres, significantly better than white-light optical profiling. Vertical resolution is typically sub-nanometer as well. Also, this method is a direct technique, mean the measurement is given as a reading and no modeling is required.

Types of Detector Tips / Probes

Depending on the model of profilometer you chose there are a number of probes that can be utilized to to provide a range of useful measurements. Most profilometers are sold with the standard detector. For small holes and tighter access you can usually purchase a small hole detector or extra small hole detector. For measuring grooves there is a groove detector and for specialty work on gears there are gear tooth detectors. See below for illustrations of these detector tip stylus combinations.