Letter Index (1011 Transducer) - Letter And Number Index; Ducer); The 1011 Transducer; The 990 Transducer - Siemens SITRANS F Operating Instructions Manual

Section 2 1010PFM-3G
2.4.6 LETTER INDEX (1011 Transducer) - LETTER and NUMBER INDEX (990 Trans-

ducer)

The 1011 Transducer

Note: The 1011 transducers utilize a different spacing method then the 990 transducers. After select-
ing the mounting method, the flow computer checks entries for pipe size, transducer type, etc., and
then recommends a number index. Use this number index to position the transducers at the proper
distance apart when using a track or spacer bar. One transducer is positioned at the REF point and the
other is positioned at the given Number Index. While this positioning provides the best signal strength
in most cases, there are situations where either more signal quality or more amplitude is desired. This
can be accomplished by moving the cursor to [Spacing Offset] and selecting either "Min" for a better
signal quality, or "Max" for greater amplitude. After selecting "Min" or "Max", the computer will recom-
pute a different Number Index. Move the transducer to that new position.

The 990 Transducer

This menu provides both a Letter Index and a Number Index. The Number Index (like the 1011) pro-
vides the spacing between transducers while Letter Index provides for changes, if necessary, for
signal strength and amplitude. Higher letter indices provide greater signal levels but, in some cases,
slightly decreased signal quality. For transducers mounted independently and where manual mea-
surements of the distance between transducers must be determined (e.g., 1011 Transducers in direct
mode), the flow computer issues the actual distance between the transducers in inches or millimeters
(Ltn). Please review Section 3 for details on how to use the Ltn measurement. You must connect the
Up transducer cable to the transducer mounted on the upstream end of the mounting track. This lets
the meter report the flow direction correctly.
It is important that you note each transducer's serial number, its Index position during the original
installation, and whether it is in the upstream or downstream position. If you cannot recreate the origi-
nal installation's exact physical arrangement, it will be necessary to do a "New Install." In addition,
please note that transducer pairs have matching serial numbers except for the appended letters 'A"
and "B." These letter designations help you identify each transducer.

2.4.7 THE NUMBER INDEX MENU CELL

Selecting the Spacing Offset allows the flow computer to calculate the Number Index. The Number
Index establishes the spacing between a pair of transducers. You cannot override this recommenda-
tion. 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
Application Data menu. When you Invoke the [Install Completed?] routine, the flow computer actually
measures the liquid sonic velocity (Vs). In some cases, it may prompt you to re-space the transducers
to another number index.

2.4.8 THE Ltn MENU CELL

This view only menu cell shows the distance in inches or millimeters between the front faces of the
transducers along the axis of the pipe. If you are mounting the transducers without a track or spacer
bar, you will have to space them according to this value (see Section 3 for details). Note that Ltn may
be a negative number for direct mount on very small pipes where the transducer spacing overlaps.
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