KROHNE CORIMASS MFC 85 EN - Manual (Page 13)

13
Case 4: Dissolved solids.
To program the converter for this case two density / concentration points are required at three
different temperatures. The three temperatures should cover the normal operating range of the
process and the concentration points should be chosen to match the normal operating span of
concentrations over which maximum accuracy is required.
Temp. /°C Conc. by Mass /% Density /g/cm
3
T
1
C
11
ρ
11
C
21
ρ
21
T
2
C
12
ρ
12
C
22
ρ
22
T
3
C
13
ρ
13
C
23
ρ
23
This data should then be input into the Microsoft Excel

CONC4.XLT spread sheet which will
then proceed to calculate the settings for the 3.10 menus. Manual solution of the equations is
possible but the Excel method is preferable as it will also produce tables and charts so the
algorithm can be compared against real data and adjustments quickly made if necessary.
To solve manually,
ρ
S
and
ρ
C
values must be calculated for each of the temperatures, T
1
, T
2
and T
3
, using the equations:
( )
( )
ρ
ρ ρ
ρ ρ
ρ
ρ ρ
ρ ρ ρ
Cn
n n n n
n n n n
Sn
n n cn
n n n cn
n
C C
C C
C
C
T
=
−
−
=
− −
1 2 1 2
1 1 2 2
1 1
1 1 1
100
for temperature
With three temperature /
ρ
C
points the Liquid
ρ
20
, K
1
and K
2
values can be calculated as
detailed for Case 2. The Solute
ρ
20
, K
1
and K
2
values can then be calculated in the same way
from the three
ρ
S
values.
Example: Aqueous Sodium Chloride Solution (NaCl).
The process operates between 10 to 30°C and is required to measure NaCl concentrations
between 5 and 15% by mass.