Myron L 6P and 4P - Manual (Page 45)

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readings for a specific solution. That value remains a constant for
all measurements, and should be reset for different dilutions or
temperatures.
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 Ultrameter II will allow the
user to attain true TDS readings that correspond to evaporated weight.
If none of the 3 standard solutions apply, the User mode must be used.
Temperature Compensation (Tempco) and TDS Derivation below, details
the USER mode.
XXII. TEMPERATURE COMPENSATION (Tempco)
and TDS DERIVATION
The Ultrameter II contains internal algorithms for characteristics of the
3 most commonly referenced compounds. The solution type in use is
displayed on the left. Besides KCl, NaCl, and 442, there is the “USER”
choice. The benefit of USER mode is that one may enter the tempco and
TDS conversion values of a unique solution via the keypad.
A. Conductivity Characteristics
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