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Fixed
Regulator
A
djustable
Regulator
Sonic
Nozzle
OR Porous Plug
DryCal
Piston or
Bell Prover
Gas
Supply
Stable Pressure
> 200 kPa
Figure 6 Alternative Setup for Piston Provers
7.2 Vacuum Comparison of Cal=Trak with Piston or Bell Provers
The Cal=Trak operates similarly in both pressure and suction applications. Sometimes, however, users wish to compare the Cal=Trak under
suction (vacuum) conditions. With a piston or bell prover, the setup of Figure 7
can be used. Note that the inlet to the Cal=Trak is at
atmospheric pressure.
The restrictor should be sized to provide a drop of at least 70 kPa (21 inches or 500 mm Hg). The purpose of the restrictor is to render the
piston insertion pressure change (0.1 kPa) relatively insignificant, as in the similar pressure calibration methodology.
In volumetric, comparisons, it is important to compensate for the difference in outlet temperature from input temperature. Although the
pressure is the same on each end, the restrictor and the pump affect the outlet temperature and flow must be normalized to the inlet
(ambient) temperature.
DryCal
Vacuum Pump
Restrictor
Figure 7 Vacuum Setup for Piston or Bell Provers
Cal=Tra
k
Cal=Trak