Myron-l 6PFCE and 4P Bedienungsanleitung PDF herunterladen (Seite 47)

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 benet 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 xed tempco

for a limited measurement range, enter a specic 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. 15 (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. 15. 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).

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Myron-l 6PFCE and 4P Bedienungsanleitung Seite 47