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Section 6
6.4.4 REVIEWING THE SPACING METHOD
The flow computer analyzes your transducer selection, mounting mode and pipe size to determine the
best way to install your transducers. It will recommend the use of either a mounting track, a spacer
bar, or independent mounting. The flow computer will list the part number of a mounting track or spacer
bar. If it decides upon independent mounting, it will report the distance required between the two trans-
ducers. In this case, you have to make sure that when you mount the transducers, the space between
them equals the length specified in the Ltn menu cell.
6.4.5 HOW TO USE THE SPACING OFFSET
After you select the mounting method, the flow computer checks your entries for pipe size, transducer
type etc. and then recommends a spacing offset. This is the first step in establishing the correct
distance between the transducers. Spacer bars and mounting tracks utilize number indices (labels) to
simplify transducer placement. One transducer is located at the Reference position, while the other
one is located at the Number Index position. The Number Index cannot be directly edited. However, the
Spacing Offset can be changed via its option list. Changing the Spacing Offset will alter the reported
Number Index. Maximum spacing offset provides moderately greater signal levels but, in some cases,
slightly decreased zero flow stability.
If the flow computer reports "Use Ltn," you have to measure the distance between the upstream and
downstream transducers. The flow computer issues the actual distance between the transducers in
inches or millimeters (See paragraph 6.4.7 Ltn Menu Cell). Note that, even though using Ltn does not
call for the physical use of the Number Index, you can still change the Spacing Offset to influence the
strength of the transmit signal.
System 1020 uses a pair of precisely matched transducers. Therefore, you can select either one for
the Reference position. You must connect the Up transducer cable to the transducer mounted on the
upstream side of the mounting track. This lets the meter display the flow direction correctly.
It is important that you note each transducer's serial number and its Index position during the original
installation because to reinstall the flowmeter successfully, you must remount each transducer in its
original position. Transducer pairs have matching serial numbers except for the appended letters "A"
and "B." This helps you to identify each transducer.
To select a different Spacing Offset
To access to [Spacing Offset] option list press the <Right Arrow>.
To move the cursor to the desired offset press the <Up/Down Arrows>.
To store selection press <ENTER>.
6.4.6 THE NUMBER INDEX MENU CELL
Selecting the [Spacing Offset] menu cell allows the flow computer to calculate the Number Index. The
Number Index establishes the spacing between a pair of transducers. You cannot override this recom-
mendation. To complete the transducer installation, you must accept the Number Index by mounting
the transducer at that point on your spacer bar or mounting track. Initially, the flow computer bases its
Number Index selection on the pipe diameter and estimated liquid sonic velocity (Vs) you entered in the
Pipe Data menu. When you invoke the [Install Complete?] routine, the flow computer actually mea-
sures the liquid sonic velocity (Vs). In some cases, it may prompt you to re-space the transducers to
another number index.
6-19
1020NFM-1D
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