Vaisala DM70 - Manual (Page 65)

Chapter 8 ____________________________Measuring Moisture in SFB6B Gas-insulated Equipment
With DSC74B, the dewpoint can be measured at the GIE pressure. If
the measurement is done in the GIE pressure, DM70 is able to show
the corresponding dewpoint in the atmospheric pressure.
DSC74B limits the flow rate with a leakage screw. The flow rate is
optimized for GIE pressures between 3 ... 10 bar
g
, and no external
flow meter is needed. The maximum flow can also be increased by
removing the leak screw and adjusting the flow manually with the
valve. To remove the leak screw, see Figure 30 below.
0405-012
Figure 30 Removing the Leak Screw
Parts per million by volume (ppm
v
) and parts per million by weight
(ppm
w
) are frequently used to indicate humidity. The latter depends on
the molecular weight of the gas. For SF
6
, the molecular weight is
146.06, and the conversion between ppm
v
and ppm
w
is the following:
ppm
w
= ppm
v
/ 8.1
DM70 is able to show the ppm
v
and ppm
w
values for moisture.
VAISALA _______________________________________________________________________ 63