Appendix D. Measuring P And L Dimensions; Introduction; Measuring P And L Distances - GE DigitalFlow GF868 Startup Manual

Appendix D. Measuring P and L Dimensions

D.1 Introduction
When programming the
(L) must be entered. These parameters are determined by measurements on the actual transducer installation, with P
equal to the face-to-face distance between the transducers and L equal to the axial distance between the centers of the
transducer faces.
The accuracy of the programmed P and L values is critical to precise flow rate measurements. If GE supplies the
flowcell for the system, the correct values will be included in the documentation supplied with the unit. For transducers
installed on an existing pipe (see Figure 17 on page 60), P and L must be measured at the site. This appendix provides
instructions for properly determining these dimensions.
D.2 Measuring P and L Distances
Whenever possible, physically measure the face-to-face distance (P) and the axial distance (L) between the centers of
the flat faces of the transducers. Refer to Figure 17 on page 60 for an illustration of the proper distances to measure in a
typical installation.
In some situations only one of the required distances can be directly measured. When this happens, a knowledge of the
installation angle () of the transducers, permits the second distance to be calculated from the equation below:
As an example, assume that the transducer installation angle is known to be 45° and the L distance is measured to be
10.00 inches. Then, the P distance is calculated to be P = 10.00/0.707 = 14.14 inches.
With a Bias 90° transducer installation, it sometimes happens that the only known parameters are the transducer angle
() and the centerline distance between the transducer bodies (CL). In these cases, it is still possible to calculate both P
and L by combining the first equation above with the second equation below (see Figure 17 on page 60):
Standard GE 90° transducers have the face offset from the centerline of the body by 0.6 inches. Thus, a pair of
transducers has a total offset of 1.2 inches, as indicated in the second equation. For example, suppose that the
transducer installation angle is 30° and CL is measured to be 12.00 inches. Then, P = 12.00 – 1.2 = 10.80 inches and L
= 10.80 x 0.866 = 9.35 inches.
DigitalFlow™ GF868 Startup Guide (1 and 2-Channel)
menu of the Model GF868's User Program, the path length (P) and the axial dimension
PIPE
L

cos = -- -
P
P = CL 1.2 –
Appendix D. Measuring P and L Dimensions
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