Density Meter LB 444 SECTION 6. BASICS OF DENSITY MEASUREMENTS
65
During multi-point calibration, the following additional functions will be initiated
after selection of the calibration mode with <
enter
> and then <
more
> :
a) Calculation of curve function:
The curve function is calculated in accordance with the selected calibra-
tion mode from the value pairs entered and corrected as described below
(see 0 Correction of Analysis Values).
b) Calculation of the square error of the curve fit:
The quality of the calibration curve is calculated from the differences be-
tween the calculated calibration curve and the value pairs entered.
Ideally, all points exactly match the calculated curve. The square error
becomes “0”.
c) Checking the calibration curve for turning points:
With the limits of the current output values (Product Data menu) one
checks whether the curve has a monotonously rising or falling trend. If this
is not the case the error message “Curve not clear” will be displayed (see
section 0 Error Messages during Calibration).
Correction of Analysis Values
The countrate read into the Data input menu is dependent upon the density of
the product during reading-in. In the laboratory the density is usually determined
at constant temperatures. With constant concentrations but different tempera-
tures during reading in of the pulses one may get:
• the same lab values
• different density values and therefore
• different countrates.
To avoid calibration errors, the product temperature is stored as well. When cal-
culating the calibration curve, the entered laboratory value is corrected by
means of the temperature coefficient. This correction is carried out only when
• temperature compensation has been enabled in Config. Instrument
• a temperature coefficient has been entered.
The corrected lab values from which the calibration curve is calculated are dis-
played after the coefficients and the square error.
The following two points are relevant only when measuring the density. For con-
centration measurements the temperature compensation is always enabled prior
to performing calibration.
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