Emerson PN 51-FCL-1056 Calibration Free Chlorine, Procedure-Zeroing the Sensor

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MODEL FCL-1056

SECTION 6.0

 

CALIBRATION

6.3 CALIBRATION — FREE CHLORINE

6.3.1 Purpose

As Figure 6-1 shows, a free chlorine sensor generates a current directly proportional to the concentration of free chlorine in the sample. Calibrating the sensor requires exposing it to a solution containing no chlorine (zero standard) and to a solution containing a known amount of chlorine (full-scale standard).

The zero standard is necessary because chlorine sen- sors, even when no chlorine is in the sample, generate a small current called the residual current or zero cur- rent. The analyzer compensates for the residual current by subtracting it from the measured current before con- verting the result to a chlorine value. New sensors require zeroing before being placed in service, and sensors should be zeroed whenever the electrolyte solution is replaced. Either of the following makes a good zero standard:

FIGURE 6-1. Sensor Current as a Function of Free Chlorine Concentration

•Deionized water containing about 500 ppm sodium chloride. Dissolve about 0.5 grams (1/8 teaspoonful) of table salt in 1 liter of water. DO NOT USE DEIONIZED WATER ALONE FOR ZEROING THE SENSOR. THE CONDUCTIVITY OF THE ZERO WATER MUST BE GREATER THAN 50 uS/cm.

•Tap water known to contain no chlorine. Expose tap water to bright sunlight for at least 24 hours.

The purpose of the full-scale standard is to establish the slope of the calibration curve. Because stable chlorine standards do not exist, the sensor must be calibrated against a test run on a grab sample of the process liquid. Several manufacturers offer portable test kits for this purpose. Observe the following precautions when taking and testing the grab sample.

•Take the grab sample from a point as close to the FCL as possible. Be sure that taking the sample does not alter the flow of the sample to the unit. It is best to install the sample tap just downstream from the tap for the FCL.

•Chlorine solutions are unstable. Run the test immediately after taking the sample. Try to calibrate the sensor when the chlorine concentration is at the upper end of the normal operating range.

Free chlorine measurements also require a pH correction. Free chlorine is the sum of hypochlorous acid (HOCl) and hypochlorite ion (OCl-). The relative amount of each depends on pH. As pH increases, the concentration of HOCl decreases and concentration of OCl- increases. Because the sensor responds only to HOCl, a pH correc- tion is necessary to properly convert the sensor current into a free chlorine reading.

The analyzer uses either continuous (live) or manual pH correction. In continuous (live) correction the analyzer continuously monitors the pH of the sample and corrects the free chlorine reading for changes in pH. In manual pH correction, the analyzer uses the pH entered by the user for the pH correction. Generally, if the pH changes more than about 0.2 units over short periods of time, continuous (live) pH correction is recommended. If the pH is relatively steady or subject only to seasonal changes, manual pH correction is adequate.

During calibration, the analyzer must know the pH of the solution. If the analyzer is using automatic pH correction, the pH sensor (properly calibrated) must be in the process liquid before starting the calibration. If the analyzer is using manual pH correction, be sure to enter the pH value before starting the calibration.

6.3.2 Procedure-Zeroing the Sensor

1.Place the sensor in the zero standard. See Section 6.3.1 for suggested zero standards. Be sure no air bubbles are trapped against the membrane. The sensor current will drop rapidly at first and then gradually reach a stable zero value. To monitor the sensor current, press the DIAG key. Choose Sensor 1 (chlorine). The input current is the first line in the display. Note the units: nA is nanoamps, uA is microamps. Typical zero current for a new sensor is between -10 and 10 nA.

A new sensor or a sensor in which the electrolyte solution has been replaced may require several hours (occa- sionally as long as overnight) to reach a minimum zero current. DO NOT START THE ZERO ROUTINE UNTIL THE SENSOR HAS BEEN IN THE ZERO SOLUTION FOR AT LEAST TWO HOURS.

2. Press MENU. The main menu screen appears. The cursor will be on Calibrate. Press ENTER.

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Contents FCL with 1056 Analyzer Essential Instructions Free Chlorine EnglishPpm mg/L ORPLive/Continous S1 Free Cl PH Correction ManualS1 Manual pH Temp Units Calibrate Sensor 1 Free chlorine Menu TreeSensor 2 pH Temperature AlarmsDiagnostic Setup Reset AnalyzerRev. Level Date About This DocumentFCL-1056 Table of ContentsList of Tables Table of Contents CONT’DIii List of Tables CONT’DFeatures Section Description and SpecificationsApplications Specifications Sensor Specifications GeneralSpecifications Analyzer Ordering Information AccessoriesComponent Parts PH Correction required selectionThis page left blank intentionally Unpacking and Inspection Section InstallationFCL-01 free chlorine without continuous pH correction FCL-02 free chlorine with continuous pH correctionInstalling the Sensors InstallationGeneral Information Mounting, Inlet, and Drain ConnectionsModel FCL-01 This page left blank intentionally POWER, ALARM, and Output Wiring Section WiringPower Analog output wiringAlarm relay connections Sensor WiringWiring Diagram for Free Chlorine Sensor Model FCL-1056 Section Wiring Display Section Display and OperationKeypad Calibrate Programming the ANALYZER-TUTORIALOutputs RangeO1 S1 20mA 08.50 ppm Output Range O1 S1 4mA 0.000 ppmO2 S1 4mA 0.0C O2 S1 20mA 100.0C SecurityHold Using HoldMain Format Configuring the Main DisplayLanguage English Contrast Format, Language, Warning, and ContrastSection Programming the Analyzer Default SettingsGeneral Sensor assignment AlarmsChoices Default Definitions CONFIGURING, RANGING, and Simulating OutputsProgramOutput ConfigureAssign Procedure Ranging Outputs Configure Simulate Output ConfigureOutput Output Range O1 S1 20mA 10.00 ppm O2 S1 4mA 0.0C O2 S1 20mA 100.0CConfiguring Alarms and Assigning Setpoints Configure SimulateRangeSimulate OutputSection Programming the Analyzer Configure/Setpoint AlarmsAlarm Alarm Simulate Alarm Alarms Configure/SetpointSimulate Don’t SimulateSynch Timers Yes Alarms Configure/Setpoint SimulateProcedure Synchronizing Timers Definitions Chlorine Configuring the MeasurementDefinitions pH/ORP Sensor1Sensor MeasurementDefinitions pH Configuring Temperature Related SettingsTemperature Program Outputs Alarms MeasurementConfiguring Security Settings S1 Temp Comp Auto S2 Temp CompSetting UP Diagnostics Program Alarms Measurement TemperatureSecurity SecurityDiagnostic Setup Program Measurement Temperature SecurityGI Fault High 1500MΩ Procedure Setting Up Diagnostics Program Temperature Security Diagnostics Resetting the Analyzer Reset Analyzer Reset AnalyzerSection Calibration Calibrating TemperatureIntroduction Calibrate SensorSensor11 Output ProcedureS1 Calibration S1 Calibration + 25.0CCalibration Free Chlorine Procedure-Zeroing the SensorChoose Free Chlorine Calibrate SensorSensor11 Output S1 CalibrationCalibrate? Temperature S1 Calibration ZeroZeroCalCal Process CalSensor Sensor OutputCalibration Slope and Offset Calibration pHAuto ZeroBufferCalCal10.01 pH 07.01 pHStable Time Buffer ManualManual Buffer 1 0 7.00 pH S2 pH Manual Cal Buffer StandardizeStandardize Redox Temperature S2 pH Cal Buffer CalSlope 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 Analyzer Section MaintenanceReplacing the electrolyte solution and membrane Cleaning the membraneChlorine Sensor GeneralOther Maintenance Cleaning the SensorPH Sensor Constant Head Flow Controller Cleaning the flow controllerWeight Weight Using the Diagnostic Feature Section TroubleshootingFaults OverviewFault message Explanation Section Troubleshooting When a Fault Message is ShowingHardware Error Sensor ADC Error Sensor CPU ErrorSensor Incompatible Sensor RTD OpenGlass Z Too High Sensor RTD Out of RangeReference 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 Chlorine readings are too low Sensor does not respond to changes in chlorine levelCalibration Error During Two-Point Calibration Troubleshooting When no Error Message is Showing pHSensor Does Not Respond to Known pH Changes Calibration Error during StandardizationPH Readings Are Moderately Noisy and Tend to Wander Simulating Inputs Chlorine Troubleshooting When no Error Message is Showing GeneralAnod CathSimulating pH input Simulating Inputs pHSimulating temperature Simulating Inputs TemperaturePage ASIA-PACIFIC Americas HeadquartersEurope GermanyWarranty Specifications subject to change without notice
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