K-Patents PR-01-S - Manual (Page 37)

INSTRUCTION MANUAL FOR K-PATENTS PR-01-S (-AX/FM/CS) DOCUMENT/REVISION No. INM 1/14
Effective: May 15, 2009
35
5. CALIBRATION
K-Patents Process Refractometer is delivered precalibrated according to the DELIVERY DATA SHEET.
Adjustments or change of range can be made by keyboard entry (Sections 5.1 and 5.2). Larger changes of
measuring range may require mechanical zero adjustments (Section 5.5). For sensor rangeability, see
Section 5.6.
Field calibration
The final calibration to obtain full accuracy is made by sending data to K-Patents or local K-Patents
representative for calculations (Section 5.3.).
Temperature calibration is explained in Section 5.8.
5.1. OUTPUT CURRENT RANGE SELECTION
It is possible to change the concentration range of the output current, also when the instrument is installed
and operating.
Example: To change 4-20 mA = 15 - 25 CONC% to 4-20 mA = 10 - 30 CONC%, key in the sequence
Calibrate/Parameters/Output signals/Current output and then enter Zero = 10 and Span = 20.
Important: This change is useful only if the TEST value is correct over the entire new range, see Section
5.6.
5.2. CONCENTRATION CALIBRATION FROM KEYBOARD
The concentration display should be in agreement with laboratory determinations. Deviations can be
corrected from keyboard if the diagnostic message is Normal operation. If the TEST display is outside the
range 20 - 246 (High concentration or Low concentration messages) mechanical adjustment is needed
(Section 5.5).
Off-set adjustment:
A change of the calibration constant Bias influences the CONC% reading the same amount. Key in
Calibrate/Parameters/CONC (RI)/Parameters/Bias to read and change the Bias.
Example: If the CONC% display is 26% and the laboratory determination is LAB% = 28%, then a value
Bias = 23.456 should be changed to Bias + LAB% - CONC% = 25.456.
Note: The CONC% reading is restricted to positive values even if the mathematical calculation gives a
negative value. For a negative CONC% the display shows "0.0". For BIAS adjustment it is useful to know
the real CONC% value. For this reason the calculated negative CONC% reading is shown in the
Calibration branch of the Selection tree, Figure 2.61.
Warning: Never try to change Bias in a day-to-day manner, or week-to-week. Frequent bias changes will
increase the measurement variation, not decrease it.
Amplification adjustment. The size of CONC% changes are directly proportional to the calibration
constant Gain. The point, where TEST = 128, is not influenced by Gain. From two measurement points the
new Gain can be estimated by the formula Gain*(LAB%1-LAB%2)/(CONC%1-CONC%2). After the
change of the Gain, the Bias has to be determined by a new sample.
The constants Square and Cube are linearity corrections that can be provided by K-Patents, see Section 5.3.