Appendix D. Ultrasonic Thickness Gauge Theory of Operation

D.1.2 Calibration

The accuracy of measurements are only as good as the accuracy and care with which the gauge has been calibrated. It is essential that the thickness gauge be calibrated (as shown on page 159) whenever the transducer is changed or you have a reason to doubt the accuracy of the readings. Periodic checks with samples of known thicknesses are recommended to verify that the gauge is operating properly.

D.1.3 Taper or Eccentricity

If the contact surface and the back surface are tapered or eccentric with respect to each other, the return echo again becomes distorted and the accuracy of measurement is diminished.

D.1.4 Acoustic Properties of the Material

There are several conditions found in engineering materials that can severely limit the accuracy and thickness range that can be measured.

D.1.4a Sound Scattering

In some materials, notably certain types of cast stainless steel, cast irons, and composites, the sound energy is scattered from individual crystallites in the casting or from dissimilar materials within the composite. This effect reduces the ability to discriminate a valid return echo from the back side of the material and limits the ability to gauge the material ultrasonically.

D.1.4b Velocity Variations

A number of materials exhibit significant variations in sound velocity from point-to-point within the material. Certain types of cast stainless steels and brass exhibit this effect due to a relatively large grain size and the anisotropy of sound velocity with respect to grain orientation. Other materials show a rapid change in sound velocity with temperature. This is characteristic of plastic materials where temperature must be controlled in order to obtain maximum precision in the measurement.

D.1.4c Sound Attenuation or Absorption

In many organic materials, such as low density plastics and rubber, sound is attenuated very rapidly at the frequencies used in normal ultrasonic thickness gaging. Therefore, the maximum thickness that can be measured in these materials is often limited by sound attenuation.

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Transport® Model PT878 Portable Liquid Flowmeter User’s Manual

Page 268
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GE PT878 user manual Calibration, Taper or Eccentricity, Acoustic Properties of the Material

PT878 specifications

The GE PT878 is a state-of-the-art portable ultrasonic flow meter designed for the precise measurement of liquid flow in various applications. As part of General Electric’s renowned instrumentation lineup, the PT878 combines innovative technology with user-friendly features, making it an invaluable tool for engineers, technicians, and plant operators.

One of the standout characteristics of the PT878 is its non-invasive measurement capability. The meter utilizes clamp-on transducer technology, allowing it to be installed on the exterior of the pipe, eliminating the need for invasive procedures which can disrupt the system or require pipe cutting. This non-contact approach not only simplifies installation but also enhances the device’s versatility, as it can be applied to a wide range of pipe sizes and materials.

The PT878 leverages advanced digital signal processing and sophisticated algorithms to provide accurate and reliable flow measurements. It operates using the time-of-flight method, whereby ultrasonic signals are sent and received through the fluid in the pipeline to determine the flow rate. This technology allows for remarkable precision, ensuring that operational efficiency can be maintained.

Moreover, the PT878 is equipped with features such as a bright, easy-to-read display, intuitive navigation, and robustness against harsh environmental conditions. Its compact and lightweight design enhances portability, making it suitable for field applications. The meter operates on battery power, providing a long-lasting solution for remote monitoring and temporary installations.

Another impressive aspect of the PT878 is its ability to measure not only water but also a variety of liquids, from hydrocarbons to chemicals. It supports multiple measurement modes, including volumetric flow and velocity, offering a level of flexibility that caters to diverse industrial needs.

In addition to flow measurement, the PT878 offers data logging capabilities, allowing users to store and analyze flow data over time. This function is vital for understanding trends, diagnosing issues, and optimizing system performance. Users can easily transfer data to computers for comprehensive analysis, enhancing operational insights.

With its combination of innovative technology, user-friendliness, and robust measurements, the GE PT878 ultrasonic flow meter stands out as a comprehensive solution for industries requiring reliable liquid flow measurement. Whether in a manufacturing plant, a water treatment facility, or any application requiring fluid monitoring, the PT878 delivers exceptional performance and accuracy.