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

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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 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 Ultrameter II features mathematically generated models for known
salt characteristics that also vary with concentration and temperature.
B. Finding the Tempco of an Unknown Solution
One may need to measure compensated conductivity of some solution
unlike any of the 3 standard salts. In order to enter a custom fixed tempco
for a limited measurement range, enter a specific value through the
User function. The tempco can be determined by 2 different methods:
1.
Heat or cool a sample of the solution to 25°C, and measure its
conductivity. Heat or cool the solution to a typical temperature
where it is normally measured. After selecting User function, set
the tempco to 0 %/°C as in Disabling Temperature Compensation,
pg. 14 (No compensation). Measure the new conductivity and the
new temperature. Divide the % decrease or increase by the 25°C
value. Divide that difference by the temperature difference.
2. Heat or cool a sample of the solution to 25°C, and measure its
conductivity. Change the temperature to a typical measuring
temperature. Set the tempco to an expected value as in User
Programmable Temperature Compensation, pg. 13. See if the
compensated value is the same as the 25°C value. If not, raise or
lower the tempco and measure again until the 25°C value is read.
C. Finding the TDS Ratio of an Unknown Solution
Once the effect of temperature is removed, the compensated conductivity
is a function of the concentration (TDS).