Flowmeter SVTU-11B, Operating Manual

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Appendix M
How to set hydraulic zero
Setting of hydraulic zero is necessary for exception of a systematic measurement error.
It is possible occurrence can be caused by difference in manufacturing and real conditions of
setting zero.
This phenomenon appears as non-zero meter indications when the real flow velocity is
equal to zero.
This action allows eliminating of a systematic measurement error from measuring re-
sults.
Device maintenance without zero setting or with incorrect zero setting can lead to sig-
nificant flow measurement errors, especially in a range of low flow rates.
Zero setting should be carried out:
−
at device commissioning;
−
after mounting (dismantling) of flow sensors (FlS) during routine maintenance;
−
after changing of order of cable connections to flow measurement section (FS);
−
at inspection of flow measurement channel functionality.
Zero setting in each water meter channel is desirable to conduct at first out of pipe (on
‘tapped’ FS) and then (it is obligatory) on the object. If there is no possibility to cut off a wa-
ter, zero setting out of pipe is a unique way for correct device commissioning. Thus it is ne-
cessary to provide repeated connection of flow measurement channels cables and FlS, which
has been used during zero setting in laboratory conditions. Thus FlS should not be disman-
tled from ‘tapped’ FS.
1 Inspection of correctness for zero setting on ‘tapped’ FS:
1.1 Assemble a flow measurement section with technological tap at the end face, lo-
cate it vertically, fix flow sensors and completely fill FS with preliminary boiled or settled
water. Clean end faces of flow sensors from remained air bubbles manually (by a finger or a
brush) if they were appeared during filling of FS.
1.2 Connect flow sensors (FlS) and resistive temperature detectors (R
Т
D) to corres-
ponding cables.
1.3 No error messages concerning flow rate and temperature measurements.
1.4 Enter the mode ‘Zero setting’ and make setting on both channels simultaneously
or separately. While setting, two groups of digits are displayed on the screen. The first one
represents the hardware information about zero water velocity. This group is stored before
following resetting. The second group shows number of zero velocity measurement cycles.
For identical FS types these numbers of measurement cycles usually coincide. For different
FS types they can be different, within the limits of 96 cycles, but do not exceed 120.
1.5 If zero setting has not been completed positively, it is necessary to check up ser-
viceability of cables, quality of connections in sockets and then repeat the previous item.
2 For successful zero setting on an object it is necessary to provide :
−
reliable water cutting off from both sides of flow measurement section by means of
valves;
−
qualitative installation and serviceability of flow sensors, temperature sensors and al-
so device entrance cables;