Myron L 6Pfc and 4P - Manual (Page 42)

38
Chart 1
0 5 10 15 20 25 30 35 40 45 50 55 60
1.500%
1.600%
1.700%
1.800%
1.900%
2.000%
2.100%
2.200%
2.300%
2.400%
2.500%
KCl % / °C
% / °C
Temperature
C. an Example of 2 different solution selections and the
resulting compensation
How much error results from treating natural water as if it were KCl at
15°C?
a tap water solution should be compensated as 442 with a tempco of
1.68 %/°C, where the KCl value used would be 1.90 %/°C.
Suppose a measurement at 15°C/59°F is 900 microsiemens of true
uncompensated conductivity.
Using a 442 correction of 10 (degrees below 25) x 1.68% indicates the
solution is reading 16.8% low. For correction, dividing by (.832) yields
1082 microsiemens as a compensated reading.
a KCl correction of 10 (degrees below 25) x 1.9% indicates the solution
is reading 19% low. Dividing by (.81) yields 1111 microsiemens for a
compensated reading. The difference is 29 out of 1082 = 2.7%.
D. A Chart of Comparative Error
In the range of 1000 µS, the error using KCl on a solution that should
be compensated as NaCl or as 442, is illustrated in Chart 2 on pg. 39.
Users wanting to measure natural water based solutions to 1% would have
to alter the internal compensation to the more suitable preloaded “442”
values or stay close to 25°C. Users who have standardized to KCl- based
compensation may want to stick with it, regardless of increasing error as
you get further from 25°C. The Ultrameter II will provide the repeatability
and convertibility of data necessary for relative values for process control.