Yokogawa EXA DC402 Dual-Channel Conductivity Analyzer - Manual (Page 72)

IM 12D08E02-01E
Appendix 10-9
10-9. WHAT IS DUAL CONDUCTIVITY?
Dual cell conductivity is a precise, comparative
measurement.
The EXA DC402G receives inputs from two
conductivity cells located at different points in
the process and compares them according to
one of six programmed user-selectable formula
- Ratio (a/b)
- Differential or linear difference (a-b)
- Percent passage (b/ax 100)
- Percent rejection {(a-b)/a x100}
- Deviation {(b/a) a x100}
- pH calculation acc. VGB directive 450L
The output signal corresponds directly to the
formulas. The EXA DC402G also displays the
absolute value of each cell on a second display
line, as desired by the user.
The unit displays all values in conductivity units
(µS/cm or mS/cm), percentage (%), resistivity
(MΩ•cm) or pH.
The pH value of the (boiler) water/condensate
is calculated from the conductivity value before
and after the cation filter according the VGB
directive 450L.
12
11
10
9
8
7
0.1 1.0 10 100
pH
SC(before) - SC(cation) / 3
pH as function of differential Conductivity
This pH calculation requires two conductivity
values which are compensated to 25ºC.
Normally matrix compensation for morpholine/
ammonia and cation are used (service code 22
should be set to 2.1 or 3.1). Consequently the
pH value displayed corresponds to 25ºC.
RETURN LINE
COOLING
TOWER
DUAL CELL
CONDUCTIVITY
RATIO
A/B
B A
MAKE-UP WATER
COOLING WATER SYSTEM
BLOW DOWN LINE
Fig. 10-2. Ratio output controls blow-down of cooling tower
based on concentration factor.
A
B
DIFFERENTIAL A-B
WASHING PROCESS
Fig. 10-3. Differential output water flow to optimize washing
efficiency.
Fig. 10-5. pH output as a function of two conductivity
values before and after the cation exchanger.
Fig. 10-4. Deviation output alarms directly after leakage in the
heat exchanger.
A
B-A X 100
(TA - TB)
SEA WATER
CONDENSATE
A
B
SEA WATER
DEVIATION
DIFFERENTIAL
TEMPERATURE
HEAT EXCHANGER