Flux FMC 100, Original Main Operating Instructions

Page: 22 / 60

22 / 60 Operating Instructions FMC
ENGLI
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4.2 Filling Accuracy with the FMC Nutating Disc Meter
The accuracy of the filling process depends on the precision of the nutating disc and its
bearing, as well as the precision of the measuring chamber. All of the components in-
volved in the measuring process are made from different plastics with our design.
In addition, various different combinations of plastics are used to be able to measure as
many liquids as possible.
Sufficiently large gaps must be provided between the moving parts to compensate for
manufacturing tolerances, material changes, for instance volumetric expansion of the
plastic due to temperature changes or swelling due to chemical processes. This results
in a fundamental inaccuracy of the measuring units.
A minimum flow rate is needed to operate the measuring unit, as construction-related
friction must be overcome to move the nutating disc and there are also gaps through
which the liquid can flow without the nutating disc moving.
Tests have shown that 100 % operation cannot be achieved when flow speeds of less
than 5 l/min are used.
The influence of friction and the gaps is so great at between 5 l/min and 20 l/min that
there is no linear relationship between the flow rate and measuring accuracy. It is then
necessary to maintain the flow rate constant and determine the deviation at this operat-
ing point. This deviation from the actual measuring volume can be compensated for
with a calibration constant.
A virtually linear error can be assumed at a measuring range of between 20 l/min and
120 l/min. A calibration constant can therefore be applied to the entire range. The
FLUXTRONIC
®
can convert the switching processes of the sensor into the volume and
display this.
A pre-requisite for as precise a filling process as possible is that the entire system is
always completely filled with liquid ("full hose system").
The following points must be taken into consideration to ensure that the above accuracy
is achieved:
-
Fill without interruption.
- The flow speed must be constant.
- The flow volume should not exceed or fall below the flow volume for which the unit
is designed.
- The temperature must be constant.
- The viscosity must be constant.
- There should be no air bubbles in the liquid.
- The opening and closing times of the valves used must always be the same.