Chapter 8. Servicing the PT878
Transport® Model PT878 Portable Liquid Flowmeter User’s Manual 159
8.3 Setting up the Thickness Gauge
For greatest accuracy in flow applications, the PT878 can measure pipe wall
thickness using an optional thickness gauge transducer, instead of relying
on the nominal pipe wall thickness. In Thickness Gauge mode, the PT878
does not measure flow, but it can determine the thickness of most standard
metal and plastic pipe materials over a range from 0.05 to 3 in. (1.3 to 76.2
mm).
The PT878 offers two basic thickness gauge functions: using the gauge to
measure thickness after entering the pipe material, and calibrating the
gauge. For the highest possible accuracy, you can also calibrate the velocity
of the pipe material.
Using the thickness gauge involves three steps:
1. Enter the material and soundspeed (refer to Figure 108 on page 160).
2. Measure the pipe wall thickness (in the Display window on page 162).
3. If the measurement seems unreasonable, examine the acoustic signal to
diagnose the problem (in the Graph window on page 163).
Calibrating the thickness gauge involves up to two additional steps:
4. Calibrate the thickness gauge itself (in the Zero window on page 165).
5. Calibrate the velocity of the pipe material (in the Velocity window on
page 168), if possible and
if the pipe material is not the material entered
in the Zero window. This step requires a trustworthy reference, either a
section of pipe (such as a flange or open pipe section) that can be
measured with calipers or another measurement device, or a thickness
calibration block from the same pipe material.
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