BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI - Universitatea ...

Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010 169
Figure 1 shows a functional diagram for pneumatic load cell for the drying
process, which can be used for proving that force change occurs slowly and
processes take place in a single direction.
Fig. 1 – Functional diagram of pneumatic force transducer.
Force measuring Fmas(t) is applied on top of a rod (4) attached to the rigid
center (3) of an embossed flexible membrane (2) with effective diameter Def
and constant effective area Sef, mounted on a body (1). On the rod (4) is
attached a nozzle (5), with the diameter dd, which is based on a ball (6) with
diameter db, closing the chamber as air access to the outside through holes in the
membrane, rigid centre and rod.
The measurement chamber can be connected in parallel with an air capacity
Vad. Pneumatic circuit supply is done by RP variable air resistance and DP
distributor type 2x2. Pressure source must be pal ≥ 1,5 pmas max.
Pressure measured pmas (t) is applied to a converter p / U, which gives the
output voltage yF∈[1, 3] Vdc.
The steady, the balance of forces, pressure pmas (t) in the enclosure is:
(1)
p
F
( t)
+ G
mas em
mas ( t)
=
,
S ef
where: Gem is the weight of mobile equipment, which is constant.
For measuring a force with some variation, included in the measurement,
the supply with compressed gas is sampled with an u1 order form, short pulse,
which provides increased pressure pmas to Fmas balance; then the rigid centre,
membrane and nozzle amount of the ball with h(t) and excess flow gas Dev(t) is
discharged outside.
For measuring a force with a change in one respect, specific processes of
drying, the weight of bodies during drying decreases continuously, it is
necessary to supply compressed gas only at the beginning of drying burden.
During drying Fmas decreases continuously, pmas decreases continuously, and
additional gas is discharged outside through the space between the gasket and
valve, to maintain balance as it shows the Eq. (1).