Emerson Process Management 53eA Sensor does not respond to changes in chlorine level

Page 99

MODEL 54eA

SECTION 16.0

 

TROUBLESHOOTING

16.5.6 Sensor does not respond to changes in chlorine level.

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

B.Is the pH compensation correct? (Applies only to the 499ACL-01 sensor.) If the controller is using manual pH correction, verify that the pH value in the controller equals the actual pH to within ±0.1 pH. If the controller is using automatic pH correction, check the calibration of the pH sensor.

C.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. Replace the electrolyte solution.

D.Replace the sensor.

16.5.7 Chlorine readings spike following sudden changes in pH (499ACL-01 only).

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

16.5.8 Chlorine readings are too low.

A.Was the sample tested as soon as it was taken? Chlorine solutions are unstable. Test the sample immediate- ly after collecting it. Avoid exposing the sample to sunlight.

B.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. Because the residual current is subtracted from subsequent measured currents, zeroing before the current is a mini- mum 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%. 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 now 1.8%. The absolute difference between the reading remains the same, 0.02 ppm.

C.Sensor response depends on flow. If the flow is too low, readings will be low and flow sensitive. Verify that the flow past the sensor equals or exceeds the minimum value. See the sensor instruction manual for recom- mended flows.

16.6 TROUBLESHOOTING WHEN NO FAULT MESSAGE IS SHOWING - TOTAL CHLORINE

Refer to the instruction manual for the TCL for a complete troubleshooting guide.

93

Page 98 Page 100
Image 99
Page 98 Page 100
Contents Amperometric Hart Analyzer/Controller Model 54eAEssential Instructions Page Model 54eA ANALYZER/CONTROLLER 13.0 10.011.0 12.0List of Figures Section TitleIii Features and Applications Section SpecificationsWeight/Shipping Weight 5 lb/6 lb 2 kg/2.5 kg Specifications GeneralPower Output Accuracy ± 0.05 mA AlarmsSpecifications Ozone Specifications OxygenSpecifications Free Chlorine Specifications Total Chlorine115/230 VAC, 50/60 Hz Power Ordering Information24 VDC Section Installation InstallationUnpacking and Inspection Pipe mounting Pipe and Wall Mounting DimensionsPanel mounting Panel Mounting DimensionsSection Wiring POWER, ALARM, and Output WiringGeneral 454EPH02 Sensor Wiring Wiring Model 499A oxygen, chlorine, and ozone sensorsGeneral 4054eA01 4054eA03 4054eA02 4054eA04 4054eA07 Display Alarm StatusSection Display and Operation General DescriptionProgram Settings List Section Software ConfigurationChoices Factory Settings Configure Choices Factory Settings Temperature compensation Section Menu Tree for the 54eA Controller Main Menu Main Alarm 2 setpoint Alarm setpointsRanging the Outputs MA 0.00 ppm 20 mA 20.00 ppm Output 1 12.00 mASetpoint 1.000 ppm 4mA 0.000 ppm 20mA 10.00 ppm Alarm setpointsOutput setpoints Simulated testTest alarm 1 Open Simulated testsTest output Display ConfigureDisplay contrast Timeout On Temp units C Output 1 mA Output 2 mALanguage English Display left Display right Out Outputs Output 1 controlOutput Measurement Range 4-20 mA Dampen 0 sec Hold Last Value Ctrl mode NormalOutput 1 Setup Output 1 ControlUsing hold Hold setupAlarm Control Settings Changing Alarm ParametersAlways configure the control parameters Before making Changes in the alarm setupAlarm Low Setpoint 0.000 ppm Alarm 1 controlAlarm 1 setup Alarm 2 controlHigh Alarm Low AlarmFeed limit timer setup Alarm FaultFeed limit Disable Timeout 3600 secInterval timer setup Alarm 4 setup Feed limit timerInterval timer Timer Disable Timer Time activated Interval 24.0 hrPH comp Manual PH value 7.00 pH PH sensor EnablePH sensor Disable Using the 499ACL-01 sensorDiagnostics Off Glass imp lo 20 MΩAutocal Standard Operate iso 7.00 pH Sensor iso 7.00 pH Temp coeffTemp comp Manual Temp units C Temperature Compensation and Temperature UnitsTemp comp Auto Temp units CNoise Reduction 60 HzMain sensor cal Bar meas Auto Bar units mm HgBarometric Pressure Lock all Lock program Lock configNoise rejection Main sensor cal SecurityController Mode Priority Condition DefinitionsAction Definitions Introduction Section Calibration TemperatureTemperature Calibration Adjust temp + 025.1 CDissolved Oxygen Concentration Section Calibration Dissolved OxygenZeroing the Sensor Sensor must be in zero solutionCalibrating the Sensor in AIR Stabilizing . . . WaitSection Calibrating the Sensor Against a Standard Instrument Calibrate 8.32 ppmCalibrating Barometric Pressure Zero main sensor Adjust temperatureCalibrate main sensor StandardizeSensor Current as a Function of Free Chlorine Concentration Section Calibration Free Chlorine 499ACL-01Calibrate main sensor Full Scale Calibration Calibrate 1.100 ppmDual Slope Calibration Dual range calOutput trim Calibrate low pointCalibrate high point Low point 2.000 ppmIntroduction Section Calibration Free Chlorine 498CL-01Ppm 100ppm 000 ppm Section Calibration Free Chlorine 498CL-01 Section Calibration Total Chlorine This page intentionally left blank Sensor Current as a Function of Monochloramine Concentration Section Calibration MonochloraminePpm 100ppm Sensor Current as a Function of Ozone Concentration Section Calibration OzonePpm 100ppm PH at 25C Standards Nominal pH SectionAutomatic TWO-POINT Calibration Autocal buffer10.02 pH Calibrate point Pt 04.00pH 25CManual TWO-POINT Calibration Pt 4.00pH 25.0C 10.01 pHPt calibration Standardize pH pH slope Standardization ONE-POINT CalibrationPH slope 60.00 mV/pH Trimming the Outputs Section Calibration Current OutputsPID Control Code Section PID and TPC ControlProportional Gain Plus Integral Reset Control Loop Adjustment and TuningProcess Reaction Curve Method Process Reaction Curve Section Time Proportional Control TPC Mode Code Overview Section TroubleshootingTroubleshooting When a Fault Message is Showing Fault message Explanation See SectionPH low or high input voltage Temperature error low or highHigh input current Check sensor zeroFailure factory and Failure eeprom Troubleshooting When no Fault Message is Showing OxygenProblem See Section Sense line openPossible error warning during in-process calibration Zero current is too highZero reading Is unstable Sensor does not respond to changes in oxygen level Barometric pressure reading is too high or too low Process readings are erratic Readings driftZero current is unstable ProblemSensor can be calibrated, but the current is too low Chlorine readings are too low Sensor does not respond to changes in chlorine levelProblem See Section Sensor does not respond to changes in monochloramine level Readings are too low Troubleshooting When no Fault Message is Showing Ozone Ozone readings are too low Sensor does not respond to changes in ozone levelTroubleshooting When no Fault Message is Showing pH Controller will not accept manual slope Sensor does not respond to known pH changes100 101 Process pH readings are noisySensor Polarizing Voltage Resistance Expected current Troubleshooting not Related to Measurement ProblemsProblem Action Simulating Inputs Dissolved OxygenSimulate Chlorine and Ozone 103 Simulating Inputs Other Amperometric MeasurementsSimulating pH input when the preamplifier is in the sensor Voltage mV PH at 25C104 Simulating Temperature Simulating temperature105 106 Measuring Reference VoltageReplacement Parts Part Number Description Section MaintenanceGeneral Section Return of MaterialWarranty Specifications subject to change without notice
Top Page Image Contents