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4. DATA REDUCTION
4.1 Calculation of Sensor Elevation
Readings can be used to calculate the elevation of the sensor and to plot them on a graph versus
time. The graph should also show the elevation of the fill above the sensor at the time of each
reading. A plot of temperature can also be included. For the standard 4650 settlement system,
using type 4500SV or 4500ALV transducers, the readings will get smaller as the sensors settle
relative to the reservoir.
For these sensors, the elevation (E) of the sensor is given by:
E = E
0
– (R
1
– R
0
) G +
∆
E
RES
Equation 1 - Elevation
Where;
E
0
is the sensor elevation at installation.
∆
E
RES
is any change of the fluid level inside the reservoir sight glass.
(If the fluid level falls,
∆
E
RES
is negative. If the fluid level rises,
∆
E
RES
is positive.)
R
0
is the initial sensor reading.
R
1
is the subsequent sensor reading.
G is the calibration factor supplied with the sensor. (A typical calibration report supplied by the
factory is shown in Figure 6.)
For Example:
If;
E
0
= 541.62 meters
R
0
= 9030 digits
R
1
= 8800 digits
G = -0.001765 meters/digit
∆
E
RES
= –10 mm (i.e. the level of water in the reservoir sight tube is 10 mm lower than the level
measure at the time of the initial reading).
Then the new sensor elevation equals:
E = 541.62 – [(8800-9030) x -0.00175] + (–0.010)
E= 541.204 meters
In other words, there has been a settlement of 0.416 meters.
