VEGA VEGADIF 65 Chemical seal CSB - Manual (Page 13)

13
3 Planning instructions for isolating systems
Chemical seal CSB • for VEGADIF 65
36133-EN-130417
3.5 Selection of the measuring range
For instruments with chemical seals and capillaries, the zero point
shift due to the hydrostatic pressure of the fluid column in the capillar-
ies must be taken into account when selecting the measuring cell.
+ –
+
–
min.
∆
ρ
M
= 0,96 kg/dm 3
= 1,0 kg/dm 3
p
i
ρ
Fl
H1 = 0,3 m
Hv = 1,8 m
H = 1 m
Hu = 0,2 m
max.
Fig. 14: Data for selection of the measuring cell
Pressure on the minus side of the differential pressure trans-
mitter with min. level:
p
-
= p
Hv
+ p
H1
= Hv • ρ
Fl
• g + H1 • ρ
Fl
•g+ p
i
= 1.8 m • (0.96 kg/dm³ • 9.81 m/s) + 0.3 m • (0.96 kg/dm³ • 9.81m/s)
+ p
i
= 197.77 mbar + p
i
Pressure on the plus side of the differential pressure transmit-
ter with min. level:
p
+
=p
Hu
+ p
H1
= Hu •ρ
FM
• g + H1 •ρ
Fl
•g+p
i
= 0.2 m • (1 kg/dm³ • 9.81 m/s) + 0.3 m • (0.96 kg/dm³ • 9.81 m/s) +p
i
= 47.87 mbar + p
i
Differential pressure on the transmitter with min. level:
Δp
Transmitter
= p
+
- p
-
= 47.87 mbar - 197.77 mbar
= -149.90 mbar
Differential pressure on the transmitter with max. level:
Δp
Transmitter
= p
+
- p
-
+ΔH •(1.0 kg/dm³ • 9.81 m/s)
= -149.90 mbar + 98.1 mbar
Example for selection of
the measuring cell