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AQUA M A STE R4
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EL EC T R O M AG N E T I C FLO W M E T ER I N SER T I O N SEN S O R | O I/FE W4 0 0/A P - EN R E V. B
…5 Installation
Measuring the internal diameter of the pipe
When a standard full-bore electromagnetic insertion sensor is
manufactured, it is usually supplied in a nominal bore size of a
round figure anywhere between 15 and 2000 mm (for example
600 mm, 700 mm). Rarely are insertion sensors precisely this
nominal size, but it is not important as the wet flow calibration
(performed on ABB's UKAS-approved and traceable flow rigs in
the UK) compensates for small deviations in size. In the case of
a insertion sensor, clearly it can't be tested in the pipe in which
it is to be finally installed. It is therefore not possible to take
account of the difference between the nominal or expected
internal diameter of the pipe and its actual value.
Since the relationship between the point velocity measurement
and the flow depends on the area of the cross section of the
pipe (
p
x the radius squared), an error in the value of the internal
diameter of the pipe causes a much greater error in the volume
flow measurement due to the 'square effect'. Therefore it is
essential, whenever possible, to measure the internal diameter
accurately to eliminate this extra source of errors.
ABB supply an internal pipe-measuring insertion sensor
(pipe-bore gauging tool) for this purpose – see Figure 15.
The tool is used as follows:
1
Fit the tool into the back of the valve, so that the red line on
top of the fitting and the handle of the tool is in line
longitudinally with the center line of the pipe.
2
Open the valve and push the tool in gently until it touches
the other side of the pipe.
3
Back off the tool a small amount and rotate the handle
through 180° so it is again in line with the longitudinal axis of
the pipe.
4
Push the tool down again carefully until it touches the wall of
the pipe. Now, slide the small collar on the tool down to
touch the top of the fitting.
5
Pull the tool back carefully until it touches the top of the
pipe. During this withdrawal, take care not to touch the
sliding collar. This distance between the top knife-edge of
the sliding collar and the top of the fitting is the internal
diameter of the pipe. Measure this distance using a good
quality tape rule.
6
Once the diameter has been measured and recorded, push
the measuring tool back into the pipe a little then turn it
through 180° so that the handle is once more in line with the
longitudinal axis of the pipe and in the same direction as the
red line on the top fitting.
7
Retract the insertion sensor fully into its fitting and close the
valve fully.
Pipe
alignment
Figure 15 Pipe-bore gauging tool
