Jenway 3540 - Manual (Page 34)

4.12 EC Ratio Setting
The EC ratio is the factor that calculates the TDS value from the conductivity
measurement. There are a number of different international and trade standards that
specify this value. The model 3540 offers adjustment over the range of 0.5 to 0.8, this
covers all potential requirements for this value. The most common standard requires
a value of 0.60 that is the default setting. Should you require to set an alternative
value press the down arrow to highlight EC Ratio in the Conductivity Calibration set
Up screen, then press the Enter key to move the highlight to the current selection. A
data entry box will appear in the centre of the screen (as shown below). The box
around the least significant digit will be flashing to indicate that this digit can be
changed by pressing the up or down arrow keys. When this is set to the desired value
the right or left arrow keys can be used to move the flashing highlight to the other
digits, which in turn can be adjusted to the desired levels with the up or down arrow
keys. When all digits are set to the desired levels press the Enter key to confirm the
setting and return the highlight to the left-hand side of the menu. Use the Escape
[ESC] key to return to other menu levels or continue with the conductivity calibration
set up as follows.
Data entry box for setting the EC ratio for TDS measuremnts
4.13
Temperature Co-efficient Setting
Conductivity varies with temperature; this variation is dependent on the different ions
in solution and their total and respective concentrations. The temperature co-efficient
is the percentage change in conductivity per degree Celsius. Where just one ionic
species is present in solution relevant data is available and an accurate temperature
co-efficient can be entered. Where a more complex mixture of ions exists in solution
the co-efficient will need to be estimated or calculated by experiment. The default
value of 1.91 is regarded as an effective average where the temperature co-efficient
is unknown. Alternatively (and in conformance with USP standards) the temperature
co-efficient can be set to zero (where the temperature compensation is switched off)
and all calibration and sample measurement carried out at the Reference
Temperature.