Emerson 6081-P Checking the Reference Electrode, Rejuvenating Reference Electrodes

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MODEL 6081-P pH/ORP

SECTION 11.0

 

MAINTENANCE

11.3.3 Checking the Reference Electrode.

Some processes contain substances, for example, sulfides, that poison the reference electrode. Poisoning alters the electrode potential. For example, sulfide poisoning converts the reference electrode from a silver/silver chloride elec- trode into a silver/silver sulfide electrode, causing a shift in potential of several hundred millivolts.

A good way to check for poisoning is to compare the voltage of the reference electrode with a silver/silver chloride electrode that is known to be good. The reference electrode from a new sensor is the best choice. To check the sus- pect electrode, place both sensors in a beaker containing buffer or a solution of potassium chloride. Connect the ref- erence leads to a voltmeter and measure the potential difference. If the suspect electrode is good, the difference should be no more than about 20 mV. Refer to Figure 11-1. A poisoned reference electrode usually requires replace- ment.

FIGURE 11-1. Checking the Potential of the Reference Electrode.

Refer to the wiring diagram(s) for the sensors to identify the reference leads.

A laboratory silver/silver chloride reference electrode can be used in place of the second sensor. All Rosemount Analytical pH sensors have a silver/silver chloride reference, and most sensors use gelled saturated potassium chlo- ride for the fill. The potentials of a good sensor reference electrode and a saturated silver/silver chloride laboratory electrode will agree within about 20 mV.

11.3.4 Rejuvenating Reference Electrodes

Occasionally, a poisoned or plugged reference electrode can be reconditioned. Although the electrode seldom recovers completely, the procedure might extend the life of the sensor by a few weeks.

1.Clean the sensor as thoroughly as possible.

2.Soak the sensor for several hours in a hot (NOT BOILING) 3% potassium chloride solution. Prepare the solution by dissolving 3 g of potassium chloride in 100 mL of water.

3.Soak the sensor in pH 4 buffer at room temperature overnight.

4.Calibrate the sensor in buffers and retest it in the process liquid.

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Contents Model 6081-P Essential Instructions Shipping considerations for wireless products Power ModulesAbout This Document Quick Start Guide Hart PollAddress Menu Tree for Model 6081 pH Wireless Transmitter Model 6081-P pH/ORP Table of Contents CONT’D Number Title List of FiguresIii This page left blank intentionally Features and Applications Section Description and SpecificationsSpecifications General PH Range 0 to Specifications WirelessFunctional Specifications Measurement update rate 1/sec. to 1/10 minTelecommunication Compliance Hart CommunicationsFCC and IC Asset Management Solutions Considerations Section InstallationUnpacking and Inspection Preamplifier Location PRE-INSTALLATION SetupTemperature Element Reference Electrode ImpedanceSection Mounting on a Flat Surface Pipe Mounting Installing the Power Module Power Module InstallationSection This page left blank intentionally Sensor Wiring Section Sensor WiringGeneral Information This page left blank intentionally This page left blank intentionally Section Intrinsically Safe InstallationThis page left blank intentionally Section Commissioning Device Network ConfigurationNetwork Communications Verify Operation Screen B Section Display and OperationDisplay Screen a Screen CInformation Screen Messages KeypadHow the Security Code Works SecurityThis page left blank intentionally Section Operation with Model Off-line and On-line Operation Making Hart related settings from the keypadSection Programming the Transmitter Changing START-UP SettingsGeneral Purpose Choosing and Configuring the Analytical MeasurementDefinitions Choose Soln Temp Corr or Sensor Isoptntl Choose MeasurementPurpose Procedure Setting a security code Setting a Security CodeChoose Calib or Config Choose ResetTransmitter Making Hart Related SettingsResetting Factory Calibration and Factory Default Settings Procedure Installing default settingsProcedure Changing screen contrast Selecting a Default Screen and Screen ContrastProcedure Choosing a display screen Choose Default DisplayProcedure Programming the display timeout Choosing a Display TimeoutCalibrating Temperature Section Calibration TemperatureIntroduction Procedure Calibration pH and ORP SectionCalibration Slope and Offset Choose BufferCal Procedure Auto Buffer CalibrationProcedure Manual TWO-POINT Buffer Calibration Choose Standardize Procedure StandardizationProcedure Entering a Known Slope Value ORP Calibration Preparation of ORP standard solutionsThis page left blank intentionally Transmitter Maintenance Section MaintenanceOverview Cleaning Procedures Frequency of CleaningRejuvenating Reference Electrodes Checking the Reference ElectrodeCalibration Frequency ORP Sensor MaintenanceCalibration GeneralPower Module Replacement Environmental Considerations Handling ConsiderationsShipping Considerations General Section Return of MaterialThis page left blank intentionally Warranty Specifications subject to change without notice
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