Sonic Driver POCKET-UFM Wall Thickness Gauge Instruction Manual

Sonic Driver POCKET-UFM Wall Thickness Gauge Instruction Manual

Introduction

A knowledge of the thickness of the pipe wall is important for correctly installing and commissioning a clamp-on ultrasonic flowmeter to the outside of a pipe.

Using the correct wall thickness allows the user to achieve accurate flow measurement.

Although the outer diameter of the pipe can be calculated with accuracy from a measurement of circumference the value of pipe wall thickness is often poorly known, if it is known at all.

By connecting a wall thickness gauge (WTG) probe to the Pocket-UFM™ instead of flow transducers, and by selecting the WTG probe in the User Interface (UI) an accurate pipe wall thickness measurement can be made.

Simply couple the WTG probe to the outside of the pipe using acoustic coupling gel.

This measured value of pipe wall thickness can subsequently be used to accurately setup the meter to make flow measurements.

Operation

The Sonic Driver™ core ultrasonic transceiver module within the Pocket-UFM uses advanced Digital Signal Processing (DSP) techniques to make an accurate time of flight measurement as longitudinal sound waves propagate through the pipe wall;

• One element of the dual element WTG probe generates an ultrasonic pulse that propagates through the pipe wall, see figure(1).
• The ultrasonic pulse is reflected from both the outer pipe wall and the inside pipe wall, at the pipe//fluid interface.
• The ultrasonic pulse is received on the second element of the WTG probe.
• The time difference between emitting and receiving the ultrasonic pulse is measured.

Figure(1) Wall Thickness Measurement

• Using the longitudinal sound velocity for the material of the pipe wall the pipe wall thickness is calculated using equation(1).

Pipe Wall Thickness = Lsos . Tdiff / 2

Equation(1) Calculation of Wall Thickness

Where;

• Pipe wall thickness (m).
• Lsos = Pipe material longitudinal sound velocity (m/s).
• Tdiff = Measured difference in time between reflection from outer wall of pipe and inner wall of pipe (s).

2.1 Couple the WTG Probe to the Pipe

Couple the WTG probe to the pipe wall using coupling gel.
Select an area of the pipe that is ideally; bare of paint, corrosion, pitting, etc..
It is possible that no reliable, consistent measurement will be achieved on poor pipe surfaces, try a different location or prepare the surface.
Hold the WTG probe normal to the pipe wall surface and aligned to its axis as shown in figure(2).

Figure(2) Orientation of WTG Probe on Pipe

When measuring on a hot surface contact the probe to the surface for as short a time as possible to avoid heating the probe.

2.2 Starting Wall Thickness Measurement

From the HMI select Main Menu – Quick Star t. Press ENTER.

Select Transducer Type – WTG from the scrolling list. Press ENTER.

When WTG probe rather than one of the flow probes is selected the HMI menus become context driven specific to WTG measurement.
Select Pipe Material from the scrolling list. If the pipe wall material is not listed select Other from the bottom of the list and enter a value for the longitudinal sound velocity, see section 2.4.

Press ENTER.
The Pocket-UFM will begin to make wall thickness measurements.
To stop wall thickness measurement press Run/Stop.

2.3 Display Wall Thickness Measurement

There are 3 displays available when making wall thickness measurements.
Scroll between the displays by pressing the Enter key;

• Detailed measurement and diagnostic values.
• Ultrasound A-scan.
• Processed data showing measurement echo.

2.3.1 Detailed Measurement and Diagnostic Values

The display screen shows measurement values and diagnostics, see figure(3);

• T – Measured transit time (us)
• B – Peak position (Bin or data point on display x axis figure(5))
• P – Peak position interpolated (sub bin resolution)
• L – Pipe longitudinal sound velocity (m/s)
• Thickness – Measured pipe wall thickness (mm)
• S – Echo signal amplitude (dB)
• N – Electronic noise level (dB)
• Gain – Receiver gain (dB)

Figure(3) Measurement values and diagnostics

2.3.2 Ultrasound A-scan

This display screen shows an A-scan (Ultrasonic signal against time trace), see figure(4).
It is possible to see that the ultrasonic pulse reverberates and echoes many times across the pipe wall.
By rolling the WTG probe on the pipe wall it is possible to optimise the amplitude of the echoes.

Figure(4) A-scan

2.3.3 Processed Data Showing Measurement Echo

This display screen shows processed data as a graph, with the preferred echo marked with a vertical line at its peak position, see figure(5).
By rolling the WTG probe on the pipe wall it is possible to optimise the amplitude of the peaks.
The Sonic Driver DSP will preferentially pick the nearest, largest peak to the left side of the display to make its measurement.
Clearly, if the DSP should be selecting incorrectly then rolling the WTG probe can make the selection jump to the correct peak.

Figure(5) Processed Data Showing Measurement Echo

2.4 Measuring on Other pipe material

If the material of the pipe is not listed, or the user requires to use a different value to that listed for a material then the user can select the pipe material as Other.

From the menu Main Menu – Installation – Pipe the user can select option WTG SOS.

Enter a value for the longitudinal sound velocity in the pipe material and press ENTER.

NOTE : This value is only used when pipe material Other is selected. The value for a listed pipe material is not changed.

Technical Data

Sonic Driver

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