DS Europe 500QD Series, Instructions Manual

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6.2 PANS, PLANES AND STRUCTURES OF WEIGHING (see paragraph 4.2.1):
Cells with pan directly connected and solid with the load cell (i.e.: QB 700 and EG):
The pan has to be very stiff.
Flexions of about 1 mm at the edges may reduce even 10 times the measure accuracy.
To avoid increase of weight of the pan: bending beads or the use of aluminium die-
casting pans are suggested.
Cells with overhanging structures (i.e.: Series LD - MB 5000 – HC 2000 - ME –MF –
BC 300-PT500 – MP – MB490 – 560QDT- 500QD):
The applied force has to be always coincident with the weighing axis. Transversal
components of the force or torque moments introduce errors and may damage the cell.
It is advisable: the use of saddles (LD Series), spherical heads, thrust spherical plain
bearings (HC 2000), rod ends, etc. and of stiff and strong overhanging structure welded
together and never connected by screws or riveted joints.
A flexion or a displacement of few millimetres of the barycentre of the applied force may
introduce errors of 5÷20% FS.
6.3 WEIGHING SYSTEM WITH SEVERAL CELLS (see again the paragraph 4.2.1.):
The distance among the cells brings to the solution of the following installation problems:
Important: with several cell systems use only not-amplified load cells (see par. 8.1.2).
6.4.1 The radial movement between the upper structure of the cell and the lower one, due
to the difference of the thermal and mechanical expansion of the two structures: this
problem is usually limited as the upper structure is, in general, in steel and the lower
structure (= the bed-plate) is in the same metal or in reinforced concrete which has the
same coefficient of thermal expansion of the steel.
If possible, for round reservoirs lay radially the reinforcing rods. The remaining
expansion difference may be compensated by saddles, or by thrust spherical plain
bearings or by roller plates.
6.4.2 Flexion of the upper structure due to the load: it is compensated by strengthening of
the structure, by tie rods, by rod ends, by spherical bearings, etc.
In case of weighing vertical reservoirs, if possible, settle the shelfs with the load cells
at half the height, that is, at the same elevation of the barycentre of the tank.
In general, the technical cares applied on the installation are important elements to
define the quality results of the weighing system.