Emerson PN 51-FCL-1056 instruction manual Sensor does not respond to changes in chlorine level

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MODEL FCL-1056

SECTION 9.0

 

TROUBLESHOOTING

9.5.6 Sensor does not respond to changes in chlorine level.

1.Is the grab sample test accurate? Is the grab sample representative of the sample flowing to the sensor?

2.Is sample flowing past the sensor? Be sure the liquid level in the constant head sampler is level with the central overflow tube and that excess sample is flowing down the tube. If necessary, disassemble and clean the over flow sampler. See Section 8.4.

3.Is the pH compensation correct? If the analyzer is using manual pH correction, verify that the pH value in the analyzer equals the actual pH to within ±0.1 pH. If the analyzer is using automatic pH correction, check the calibration of the pH sensor.

4.Is the membrane clean? Clean the membrane and replace it if necessary. Check that the holes at the base of the cathode stem are open. Use a straightened paper clip to clear blockages. See step 4 in Section 9.5.2. Replace the electrolyte solution.

5.Replace the sensor.

9.5.7 Chlorine readings spike following sudden changes in pH (automatic pH correction).

Changes in pH alter the relative amounts of hypochlorous acid (HOCl) and hypochlorite ion (OCl-) in the sample. Because the sensor responds only to HOCl, an increase in pH causes the sensor current (and the apparent chlorine level) to drop even though the actual free chlorine concentration remained constant. To correct for the pH effect, the analyzer automatically applies a correction. Generally, the pH sensor responds faster than the chlorine sensor. After a sudden pH change, the analyzer will temporarily over-compensate and gradually return to the correct value. The time constant for return to normal is about 5 minutes.

9.5.8 Chlorine readings are too low.

1.Was the sample tested as soon as it was taken? Chlorine solutions are unstable. Test the sample immediately after collecting it. Avoid exposing the sample to sunlight.

2.Low readings can be caused by zeroing the sensor before the residual current has reached a stable minimum value. Residual current is the current the sensor generates even when no chlorine is in the sample. It is also called the zero current. Because the residual current is subtracted from subsequent measured currents, zeroing before the current is a minimum can lead to low results.

Example: The true residual current for a free chlorine sensor is 4 nA, and the sensitivity is 350 nA/ppm. Assume the measured current is 200 nA. The true concentration is (200-4)/350 or 0.56 ppm. If the sensor was zeroed prematurely when the current was 10 nA, the measured concentration will be (200-10)/350 or 0.54 ppm. The error is 3.6%. Now, suppose the measured current is 400 nA. The true concentration is 1.13 ppm, and the measured concentration is 1.11 ppm. The error is 1.8%. However, the absolute difference between the reading remains the same, 0.02 ppm.

3.Sensor response depends on flow. If the flow is too low, readings will be low and flow sensitive. Verify that the chlorine sensor is installed in the correct flow cell. See Figures 2-1 and 2-2. Verify that the liquid level in the constant head sampler is level with the central overflow tube and that excess sample is flowing down the tube. If necessary, disassemble and clean the overflow sampler. See Section 8.4.

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Contents FCL with 1056 Analyzer Essential Instructions English Free ChlorinePpm mg/L ORPLive/Continous S1 Free Cl PH Correction ManualS1 Manual pH Temp Units Calibrate Sensor 1 Free chlorine Menu TreeSensor 2 pH Alarms TemperatureDiagnostic Setup Reset AnalyzerAbout This Document Rev. Level DateTable of Contents FCL-1056Table of Contents CONT’D List of TablesList of Tables CONT’D IiiFeatures Section Description and SpecificationsApplications Specifications Sensor Specifications GeneralSpecifications Analyzer Accessories Ordering InformationComponent Parts PH Correction required selectionThis page left blank intentionally Section Installation Unpacking and InspectionFCL-01 free chlorine without continuous pH correction FCL-02 free chlorine with continuous pH correctionInstallation Installing the SensorsGeneral Information Mounting, Inlet, and Drain ConnectionsModel FCL-01 This page left blank intentionally Section Wiring POWER, ALARM, and Output WiringPower Analog output wiringSensor Wiring Alarm relay connectionsWiring Diagram for Free Chlorine Sensor Model FCL-1056 Section Wiring Section Display and Operation DisplayKeypad Programming the ANALYZER-TUTORIAL CalibrateOutputs RangeOutput Range O1 S1 4mA 0.000 ppm O1 S1 20mA 08.50 ppmO2 S1 4mA 0.0C O2 S1 20mA 100.0C SecurityUsing Hold HoldConfiguring the Main Display Main FormatLanguage English Contrast Format, Language, Warning, and ContrastSection Programming the Analyzer Default SettingsGeneral Alarms Sensor assignmentChoices Default CONFIGURING, RANGING, and Simulating Outputs DefinitionsProgramOutput ConfigureAssign Configure Simulate Output Configure Procedure Ranging OutputsOutput Output Range O1 S1 20mA 10.00 ppm O2 S1 4mA 0.0C O2 S1 20mA 100.0CConfigure Simulate Configuring Alarms and Assigning SetpointsRangeSimulate OutputSection Programming the Analyzer Configure/Setpoint AlarmsAlarm Alarms Configure/Setpoint Alarm Simulate AlarmSimulate Don’t SimulateSynch Timers Yes Alarms Configure/Setpoint SimulateProcedure Synchronizing Timers Definitions Chlorine Configuring the MeasurementDefinitions pH/ORP Measurement Sensor1SensorConfiguring Temperature Related Settings Definitions pHProgram Outputs Alarms Measurement TemperatureConfiguring Security Settings S1 Temp Comp Auto S2 Temp CompProgram Alarms Measurement Temperature Setting UP DiagnosticsSecurity SecurityProgram Measurement Temperature Security Diagnostic SetupGI Fault High 1500MΩ Procedure Setting Up DiagnosticsResetting the Analyzer Program Temperature Security DiagnosticsReset Analyzer Reset AnalyzerSection Calibration Calibrating TemperatureIntroduction Procedure Calibrate SensorSensor11 OutputS1 Calibration S1 Calibration + 25.0CProcedure-Zeroing the Sensor Calibration Free ChlorineCalibrate SensorSensor11 Output S1 Calibration Choose Free ChlorineTemperature S1 Calibration ZeroZeroCalCal Process Cal Calibrate?Sensor Sensor OutputCalibration pH Calibration Slope and OffsetZeroBufferCalCal Auto10.01 pH 07.01 pHStable Time Manual BufferManual Buffer 1 0 7.00 pH S2 pH Manual Cal Buffer Redox Temperature S2 pH Cal Buffer Cal StandardizeStandardizeSlope 56.19 mV/pH Offset S1 Enter Value 00 pHProcedure-Entering a Known Slope and Offset Output Calibration Analog OutputsMA Output Cal Meter 000 mA Trim Complete This page left blank intentionally Section Digital Communications Model FCL-1056 Section Section Maintenance AnalyzerCleaning the membrane Replacing the electrolyte solution and membraneChlorine Sensor GeneralOther Maintenance Cleaning the SensorPH Sensor Cleaning the flow controller Constant Head Flow ControllerWeight Weight Section Troubleshooting Using the Diagnostic FeatureFaults OverviewFault message Explanation Section Troubleshooting When a Fault Message is ShowingHardware Error Sensor CPU Error Sensor ADC ErrorSensor Incompatible Sensor RTD OpenSensor RTD Out of Range Glass Z Too HighReference Impedance Too High Broken GlassTroubleshooting When a Warning Message is Showing Troubleshooting When no Error Message is Showing Chlorine Process readings are erratic Sensor can be calibrated, but the current is too lowReadings drift Sensor does not respond to changes in chlorine level Chlorine readings are too lowTroubleshooting When no Error Message is Showing pH Calibration Error During Two-Point CalibrationCalibration Error during Standardization Sensor Does Not Respond to Known pH ChangesPH Readings Are Moderately Noisy and Tend to Wander Troubleshooting When no Error Message is Showing General Simulating Inputs ChlorineAnod CathSimulating Inputs pH Simulating pH inputSimulating Inputs Temperature Simulating temperaturePage Americas Headquarters ASIA-PACIFICEurope GermanyWarranty Specifications subject to change without notice