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How to Measure Wall Thickness with the PosiTector UTG Ultrasonic Thickness Gage

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Measuring wall thickness with the PosiTector UTG Ultrasonic Thickness Gage, from DeFelsko—the measure of quality.

Ultrasonic Thickness gages are used to measure the thickness of nearly any material, typically in applications where access is limited to one side. They can be used to monitor the effects of corrosion and erosion on tanks and other structures, and as a quality control tool in a manufacturing or production environment.  

When taking a measurement, an ultrasonic pulse is sent into the material, travelling through to the back side. When it encounters an interface such as air or another material, the pulse is reflected back to the probe. The time required for the pulse to propagate through the material indicates its thickness.

The PosiTector UTG Ultrasonic Thickness family of probes provide fast, accurate readings. Each PosiTector UTG probe conforms to national and international standards including ASTM E797 and includes a FREE Long-form Certificate of Calibration traceable to NIST or PTB and a two-year warranty.

The PosiTector UTG C probe series is ideal for a wide range of applications and features a 5 megahertz dual-element transducer. It is ideal for measuring the effects of corrosion on tanks, ships, and other infrastructure. For best accuracy, paint should be removed prior to measurement. Included in this series are the PosiTector UTG C with a probe on a 1m cable, the PosiTector UTG CA with integral probe ideal for one-handed operation, and the PosiTector UTG CX with a heavy-duty strain-relief and armored cable for demanding applications.

The PosiTector UTG CLF Low Frequency Probe is specifically designed for measuring attenuative materials such as cast iron. A proprietary algorithm distinguishes back wall reflections from the grain noise found in cast materials.

The PosiTector UTG M Multiple Echo Probe features thru-paint capability to quickly and accurately measure the metal thickness of a painted structure without having to remove the coating. It is also ideal for measuring blasted materials and other applications requiring a more durable wear face. The PosiTector UTG M measures three or more echoes to eliminate the effect of the coating. Multiple-echo mode can also be disabled to detect pits/flaws and increase the measurement range. The Multiple-echo method requires a parallel back wall, and extremely corroded applications may be challenging to measure.

The PosiTector UTG P Precision Probe uses a single element delay line transducer to accurately measure materials as thin as one hundred and twenty-five microns or five mils. It is ideal for measuring thin-wall plastics and light-gauge metals.

PosiTector UTG Ultrasonic Thickness probes connect to the award-winning PosiTector platform, allowing a single gage body to transform to an ultrasonic thickness gage, coating thickness gage, dew point meter, surface profile gage, soluble salt tester, hardness tester, or gloss meter.

The PosiTector gage body is available in either Standard or Advanced models. All models feature a large 2.8” touchscreen, easy-to-navigate menus, internal memory, an IP65-rated enclosure, Min Scan mode, and SmartCouple mode. Advanced models feature additional memory, Wi-Fi and Bluetooth connectivity, live graphing of measurement data, Prompted Batch mode, A-Scan with adjustable Gain, and B-Scan mode.

All PosiTector UTG Models also feature Min Scan mode, which allows the operator to scan an area while measuring continuously, recording the minimum and maximum reading. This mode is ideal for locating thin or thick areas for further investigation.

When connected to a PosiTector Advanced gage body, PosiTector UTG probes gain A-Scan and B-scan capability- features typically limited to much more expensive and complex instrumentation.

A-Scan mode displays the reflected ultrasound measured by the gage, with the travel distance of the pulse on the x axis and the strength or amplitude of the pulse on the y-axis. Using the built-in cursor, this powerful mode can be used to locate flaws and other features of the substrate.

B Scan mode plots the material thickness on the display as readings are taken, creating a virtual cross-section of the substrate. This makes it easy to visualize features or defects in the substrate.

Measuring with any PosiTector UTG probe is simple. Simply zero, verify, adjust, and measure.

For all measurements, couplant is required to help propagate ultrasound into the coating. The included gel is ideal for rough coatings and for vertical surfaces; alternatively, a drop of water is often sufficient for smooth coatings on horizontal surfaces. Only a small, pea-sized drop is necessary.

PosiTector UTG probes must be ‘zeroed’ after every reset and periodically during use. To ZERO the probe, power the gage on with the center navigation button. Apply a single drop of couplant onto the zero block. Open the gage menu and select Zero from the Cal Settings Menu and follow the onscreen prompts. When complete, the gage will double-beep and display zero on screen.

Verification ensures that the PosiTector UTG is measuring accurately at the time of use, and is typically performed at the beginning of a work shift, or if erroneous readings are suspected. Simply take measurements on a calibrated step block and ensure that the instrument is measuring within the combined tolerance of both the standard and instrument.

The PosiTector UTG is pre-configured to measure carbon or mild steel. For other materials, an adjustment is required to account for different acoustic velocities. The PosiTector UTG makes this process easy- simply select ‘material’ from the Cal Settings menu and select from a list of common materials. If the desired material isn’t listed, the acoustic velocity of the material can be entered, or a known thickness of the material can be measured at one or two points.

The PosiTector UTG is now ready to measure. Simply add a drop of couplant and place the probe flat on the surface pressing down using moderate pressure, and wait for a reading to display.

All PosiTector UTG probes are capable of scanning, where continuous measurements are taken while the probe moves across the surface. One challenge when scanning using conventional ultrasonic instrumentation is the tendency for the probe to briefly lose contact or ‘decouple’ from the surface while taking measurements, interrupting the scan. SmartCouple mode is enabled by default on all PosiTector UTG models, automatically detecting accidental decoupling and pausing measurement instead of ending the scan.

All stored measurement data can be accessed using DeFelsko’s free PosiSoft Software to create custom, professional PDF reports. Simply connect the gage body to a computer or connect via WiFi to download all stored readings from every probe for easy viewing, analyzing, and reporting all in one convenient location.  

The PosiTector UTG family is more versatile and powerful than ever, and is an ideal addition to any PosiTector Inspection kit.

Backed by DeFelsko’s renowned quality, customer service, and exceptional two-year warranty, PosiTector UTG Ultrasonic Thickness gages are the ideal choice for measuring wall thickness.

Learn more about the expanded PosiTector UTG family at