<6. Troubleshooting>
6-5
IM 12Y18A03-01EN
1st Edition : Oct. 04, 2019-00
6.2
Slope Problems
6.2.1
Low Slope
Slope less than -40 mV/decade
• Check the electrode function, clean the electrode, recalibrate the analyzer, and if the
analyzer continues to read low, replace the electrode.
• An oxygen scavenger-free sample must be used for calibration.
• Check electronics to read mV input correctly. Use electronic test kit procedure for checking
electronics function.
Ion-selective electrodes (ISE) can be shown as DC-voltage sources with 50 to 1000 Megohm; a
very high output impedance. ISEs respond to ion concentration changes with a voltage change
of approximately -59 mV/decade for monovalent anions such as iodide. Knowing electrode and
analyzers parameters like offset potential, slope, etc allows testing of various instruments by
applying a known mV voltage.
Input Signal
Expected Reading: ± (0.5 mV + 0.1%)
0 mV
- 0.5 mV to + 0.5 mV
- 1000 mV
-1001.5 mV to – 998.5 mV
+ 1000 mV
+ 998.5 mV to + 1001.5 mV
• Standards contaminated or incorrectly made – verify calibration with fresh standards.
• Standard 1 and standard 2 values not set correctly – check the percent flow rate setting and
range setting on the dynamic calibrator and in the setup mode of the analyzer. If using a
custom standard, verify the values for the dynamic calibrator.
• Standard 1 and standard 2 added in wrong sequence – check the sequence of the
standards and repeat the calibration.
• pH adjustment is not correct – check the level and flow of the reagent. Replace the reagent
if it is contaminated or the level is less than 50 mL. Refer to Section 2.4, Installation of
Reagent and Diffusion Tubing.
6.2.2
High Slope
Slope greater than -75 mV/decade
• Improper calibration technique – refer to Section 4.4, Performing a DYN Calibration.
• Calibration standards contaminated – repeat the calibration using fresh standards.
• Electronics failure – reset the analyzer. Refer to Section 6.4, Resetting the Analyzer.
• Improper dynamic calibrator settings – refer to Section 4.4, Performing a DYN Calibration.
• An oxygen scavenger-free sample must be used for calibration.
• Cables interchanged – verify wiring of cable connections to terminal strip. Refer to Section
2.3, Wiring the Analyzer.
• Check the connection of the cable markers for the corresponding electrode. Cable markers
are the white tape at the cap connector on the cable.
• “Ref” for the reference electrode.
• “Sensing” for the iodide electrode.
• Sensing electrode coated – clean or replace the sensing electrode.