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How to Measure Surface Profile with PosiTector SPG Digital Depth Micrometer

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Steel surfaces are frequently cleaned by abrasive impact prior to the application of protective coatings. This process removes previous coatings and roughens the surface to improve coating adhesion. The resultant surface profile is comprised of a complex pattern of peaks and valleys which must be accurately measured to ensure long-term coating performance.

A surface profile height that is too low may reduce coating adhesion and corrosion resistance. Too high and the peaks may receive insufficient coverage leading to premature rusting, and requiring additional paint to cover the anchor profile.

The PosiTector SPG Surface Profile Gage is popular for users who want a fully-digital test with zero per-test cost. The digital depth micrometer is fitted with a fine-pointed probe to measure and record peak-to-valley surface profile heights in accordance with ASTM D4417 method B and SSPC PA 17. During testing, a flat base rests on the highest peaks and a spring-loaded tip drops into the valleys.

A fast measurement rate of over 50 readings per minute makes it ideal for quickly measuring surface profile over large areas. All probes feature a durable alumina wear face and field replaceable tungsten carbide probe tips for long life and continuous accuracy. PosiTector SPG probes connect to the interchangeable PosiTector Platform, quickly transforming from a surface profile gage to a coating thickness gage, dew point meter, gloss meter, and more.

DeFelsko’s other solution for measuring surface profile, the PosiTector RTR Replica Tape Reader, uses industry-standard Textex Tape to measure profile height. Models are also available that can create 3D images from the replica tape to measure peak count and other surface profile parameters. Learn more about the PosiTector RTR in the “How to Use Replica Tape to Measure Surface Profile” video at the Link in the description below.

The PosiTector SPG is available as an integral model for one-handed operation or a cabled model for improved ergonomics in hard to reach areas. The PosiTector SPG OS model features a V-groove and proprietary OD mode for measuring convex surfaces with outside diameters greater than 3 millimeters or an eighth of an inch, such as on pipes and tanks.

Additional models are available with a greater range and rounder tip for measuring the profile of textured coatings, the PosiTector SPG CS, and for measuring the profile of concrete, the PosiTector SPG TS.

Measuring surface profile with the PosiTector SPG is easy. First, verify that the instrument is operating correctly by placing the included shim on top of the glass zero plate. Place the tip of the probe on the glass while the base rests on both sides of the shim. Ensure the reading on the instrument is within the combined tolerance of the shim and the gage.

During testing, a flat base rests on the highest peaks and a spring-loaded tip drops into the valleys. Ensure that the surface is free of dust and other contaminants, then place the probe foot level on the surface to be measured. The profile height is displayed on the gage.

ASTM D4417 recommends taking ten readings at each location and recording only the maximum value, discarding any unusually high readings that cannot be repeated in an area. Average the maximum values at multiple locations and report it as the profile height. SSPC-PA17 recommends averaging the maximum values at a minimum of three locations to determine the profile height.

On competitive instruments, this method is challenging to follow and requires writing down many readings. PosiTector SPG Advanced models feature SmartBatch, making this process easy by automatically keeping only the highest reading in each spot, and averaging several spots together right on the gage.

Once measurement is complete, connect to the included PosiSoft Desktop software using a USB cable or WiFi to archive and manage measurements. Professional, custom reports can instantly be generated, including multi-batch reports

Depth micrometers such as the PosiTector SPG have no per-test cost and are a quick, reliable way of determining surface profile. Learn about all of the features and benefits of measuring surface profile with the PosiTector SPG at