Myron L PS9TK User Manual
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C. When does it make a lot of difference?
First, the accuracy of temperature compensation to 25°C determines the
accuracy of any TDS conversion. Assume we have industrial process
water to be pretreated by RO. Assume it is 45°C and reads 1500 µS
uncompensated.
1.
If NaCl compensation is used, an instrument would report 1035
µS compensated, which corresponds to 510 ppm NaCl.
2.
If 442 compensation is used, an instrument would report 1024
µS compensated, which corresponds to 713 ppm 442.
The difference in values is 40%.
In spite of such large error, some users will continue to take data in
the NaCl mode because their previous data gathering and process
monitoring was done with an older NaCl referenced device.
Selecting the correct Solution Type on the P
OOL
P
RO
will allow the
user to attain true TDS readings that correspond to evaporated
weight.
XXi. TEMPERaTuRE cOMPEnSaTiOn (Tempco) and TDS
DERivaTiOn
The P
OOL
P
RO
contains internal algorithms for characteristics of the 3
most commonly referenced compounds. The solution type in use is
displayed on the left.
When taking conductivity measurements, the Solution Selection
determines the characteristic assumed as the instrument reports what
a measured conductivity would be if it were at 25°C. The characteristic
is represented by the tempco, expressed in %/°C. If a solution of 100
µS at 25°C increases to 122 µS at 35°C, then a 22% increase has
occurred over this change of 10°C. The solution is then said to have a
tempco of 2.2 %/°C.
Tempco always varies among solutions because it is dependent on
their individual ionization activity, temperature and concentration.
This is why the P
OOL
P
RO
features mathematically generated models
for known salt characteristics that also vary with concentration and
temperature.