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Hach COD – 203 Online CODMn (Permanganate Index) Analyzer User Guide

I. Product Overview and Basic Principles

1.1 Product Introduction

The Hach COD – 203 online CODMn (permanganate index) analyzer is a precision instrument specifically designed for the automatic monitoring of the chemical oxygen demand (COD) concentration in industrial wastewater, river, and lake water bodies. Manufactured in accordance with the JIS K 0806 “Automatic Measuring Apparatus for Chemical Oxygen Demand (COD)” standard, this device employs fully automated measurement operations and adheres to the measurement principle of “Oxygen Consumption by Potassium Permanganate at 100°C (CODMn)” specified in the JIS K 0102 standard.

1.2 Measurement Principle

This analyzer utilizes the redox potential titration method to achieve precise determination of COD values through the following steps:

Oxidation Reaction: A定量 (fixed) amount of potassium permanganate solution is added to the water sample, which is then heated at 100°C for 30 minutes to oxidize organic and inorganic reducing substances in the water.
Residual Titration: An excess amount of sodium oxalate solution is added to react with the unreacted potassium permanganate, followed by titration of the remaining sodium oxalate with potassium permanganate.
Endpoint Determination: The mutation point of the redox potential is detected using a platinum electrode to calculate the amount of potassium permanganate consumed, which is then converted into the COD value.

1.3 Technical Features

  • Measurement Range: 0 – 20 mg/L to 0 – 2000 mg/L (multiple ranges available)
  • Measurement Cycle: 1 hour per measurement (configurable from 1 – 6 hours)
  • Flow Path Configuration: Standard configuration is 1 flow path with 1 range; optional 2 flow paths with 2 ranges
  • Measurement Methods: Supports acidic and alkaline methods (applicable to water samples with high chloride ion content)
  • Automation Level: Fully automated process including sampling, reagent addition, heating digestion, and titration calculation

II. Equipment Installation and Initial Setup

2.1 Installation Requirements

Environmental Requirements:

  • Temperature: 5 – 40°C
  • Humidity: ≤85% RH
  • Avoid direct sunlight, corrosive gases, and strong vibrations

Water Sample Requirements:

  • Temperature: 2 – 40°C
  • Pressure: 0.02 – 0.05 MPa
  • Flow rate: 0.5 – 4 L/min
  • Chloride ion limit: ≤2000 mg/L (for the 20 mg/L range)

Power and Water Supply:

  • Power supply: AC100V ± 10%, 50/60 Hz, maximum power consumption 550 VA
  • Pure water supply: Pressure 0.1 – 0.5 MPa, flow rate approximately 2 L/min

2.2 Equipment Installation Steps

Mechanical Installation:

  • Select a sturdy and level installation base.
  • Secure the equipment using four M12 × 200 anchor bolts.
  • Ensure the equipment is level and maintain a maintenance space of ≥1 m around it.

Pipe Connection:

  • Sampling pipe: Rc1/2 interface, recommended to use transparent PVC pipes (Φ13 or Φ16)
  • Pure water pipe: Rc1/2 interface, install an 80-mesh Y-type filter at the front end
  • Drain pipe: Rc1 interface, maintain a natural drainage slope of ≥1/50
  • Waste liquid pipe: Φ10 × Φ14.5 dedicated pipe, connect to a waste liquid container

Electrical Connection:

  • Power cable: 1.25 mm² × 3-core shielded cable
  • Grounding: Class D grounding (grounding resistance ≤100 Ω)
  • Signal output: Dual-channel isolated output of 4 – 20 mA/0 – 1 V

III. Reagent Preparation and System Preparation

3.1 Reagent Types and Preparation

Reagent 1 (Acidic Method):

  • Take 1000 g of special-grade silver nitrate.
  • Add pure water to reach a total volume of 5 L.
  • Store in a light-proof container and connect with a yellow hose.

Reagent 2 (Sulfuric Acid Solution):

  • Prepare 2 – 3 L of pure water in a container.
  • Slowly add 1.7 L of special-grade sulfuric acid (in 6 – 7 batches, with an interval of 10 – 20 minutes).
  • Add 5 mmol/L potassium permanganate dropwise until a faint red color is maintained for 1 minute.
  • Add pure water to reach 5 L and connect with a green hose.

Reagent 3 (Sodium Oxalate Solution):

  • Take 8.375 g of special-grade sodium oxalate (dried at 200°C for 1 hour).
  • Add pure water to reach 5 L and connect with a blue hose.

Reagent 4 (Potassium Permanganate Solution):

  • Dissolve 4.0 g of special-grade potassium permanganate in 5.5 L of pure water.
  • Boil for 1 – 2 hours, cool, and let stand overnight.
  • Filter and titrate to a concentration of 0.95 – 0.98.
  • Store in a 10 L light-proof container and connect with a red hose.

3.2 System Initial Preparation

Electrode Internal Solution Preparation:

  • Dissolve 200 g of potassium sulfate in 1 L of distilled water at 50°C to prepare a saturated solution.
  • Take the supernatant and dilute it with 1 L of distilled water.
  • Inject the solution into the comparison electrode container to fill one-third of its volume.

Heating Tank Oil Filling:

  • Inject approximately 500 mL of heat transfer oil through the hole in the heating tank cover.
  • The oil level should be between the two liquid level marks.

Pipe Flushing:

  • Open the sampling valve and pure water valve to expel air from the pipes.
  • Start the activated carbon filter (BV1 valve).
  • Set the flow rate to 1 L/min (PV7 valve).

IV. Detailed Operation Procedures

4.1 Power-On and Initialization

  • Turn on the power supply and confirm that the POWER indicator light is on.
  • Load the recording paper (76 mm wide thermal paper).
  • Perform Reagent 4 filling:
    • Enter the maintenance menu and select “Reagent 4 Injection/Attraction”.
    • Confirm that the liquid is purple and free of bubbles.

Preheating:

  • Check the heating tank temperature (INPUT screen).
  • The temperature must reach above 85°C before measurement can begin.

4.2 Calibration Procedures

Zero Calibration:

  • Enter the ZERO CALIB screen.
  • Set the number of calibrations (default is 3 times).
  • Start the calibration using activated carbon-filtered water.
  • Confirm that the calibration value is within the range of 0.100 – 2.500 mL.

Span Calibration:

  • Enter the SPAN CALIB screen.
  • Select the range (R1 or R2).
  • Use a 1/2 full-scale sodium oxalate standard solution.
  • Confirm that the calibration value is within the range of 4.000 – 8.000 mL.

Automatic Calibration Settings:

  • Parameter B07: Set the calibration cycle (1 – 30 days).
  • Parameter B08: Set the calibration start time.
  • Parameter B09: Set the date for the next calibration.

4.3 Routine Measurement

Main Interface Check:

  • Confirm that the “AUTO” status indicator light is on.
  • Check the remaining amounts of reagents and the status of the waste liquid container.

Start Measurement:

  • Select “SAMPLE” on the OPERATION screen.
  • The system will automatically complete the sampling, heating, and titration processes.

Data Viewing:

  • The DATA screen displays data from the last 12 hours.
  • The CURVE screen shows the titration curve shape.
  • Alarm information is集中 (centrally) displayed on the ALARM screen.

V. Maintenance Procedures

5.1 Daily Maintenance

Daily Checks:

  • Reagent and waste liquid levels.
  • Recording paper status and print quality.
  • Leakage in pipe connections.

Weekly Maintenance:

  • Activated carbon filter inspection.
  • Backflushing of the sampling pipe.
  • Solenoid valve operation test.

5.2 Regular Maintenance

Monthly Maintenance:

  • Cleaning and calibration of the measuring device.
  • Cleaning of the reaction tank and electrodes.
  • Replacement of control valve hoses.

Quarterly Maintenance:

  • Replacement of heating oil.
  • Inspection and replacement of pump diaphragms.
  • Comprehensive flushing of the pipe system.

Annual Maintenance:

  • Replacement of key components (electrodes, measuring devices, etc.).
  • Comprehensive calibration of system parameters.
  • Lubrication and maintenance of mechanical components.

5.3 Reagent Replacement Cycles

  • Reagent 1 (Silver Nitrate): Approximately 14 days/5 L
  • Reagent 2 (Sulfuric Acid): Approximately 14 days/5 L
  • Reagent 3 (Sodium Oxalate): Approximately 14 days/5 L
  • Reagent 4 (Potassium Permanganate): Approximately 14 days/10 L

VI. Fault Diagnosis and Handling

6.1 Common Alarm Handling

AL – L (Minor Fault):

  • Symptom: Automatic measurement continues.
  • Handling: Check the alarm content and press the ALLINIT key twice to reset.

AL – H (Major Fault):

  • Symptom: Measurement is suspended.
  • Typical Causes:
    • Abnormal heating temperature: Check the heater, SSR, and TC1 sensor.
    • Full waste liquid tank: Empty the waste liquid and check the FS2 switch.
    • Abnormal titration pump: Check the TP pump and SV16 valve.

6.2 Analysis of Abnormal Measurement Values

Data Drift:

  • Check the validity period and preparation accuracy of reagents.
  • Verify the response performance of electrodes.
  • Re-perform two-point calibration.

No Data Output:

  • Check the sampling system (pump, valve, filter).
  • Verify that parameter G01 = 1 (printer enabled).
  • Test the signal output line.

Large Data Deviation:

  • Perform manual comparison tests.
  • Adjust conversion parameters (D01 – D04).
  • Check the representativeness of sampling and pretreatment.

VII. Safety Precautions

7.1 Safety Sign Explanations

  • Warning: Indicates a serious hazard that may cause severe injury or death.
  • Caution: Indicates a general hazard that may cause minor injury or equipment damage.
  • Important: Key matters for maintaining equipment performance.

7.2 Safety Operation Procedures

Personal Protection:

  • Wear protective gloves and glasses when handling reagents.
  • Use a gas mask when handling waste liquid.

Chemical Safety:

  • Dilute sulfuric acid by adding “acid to water”.
  • Avoid contact between potassium permanganate and organic substances.
  • Store silver nitrate solution in a light-proof container.

Electrical Safety:

  • Do not touch internal terminals when the power is on.
  • Ensure reliable grounding.
  • Cut off the power supply before maintenance.

High-Temperature Protection:

  • The reaction tank reaches 100°C; allow it to cool before maintenance.
  • Heating oil may cause burns.

VIII. Technical Parameters and Appendices

8.1 Main Technical Parameters

  • Measurement Principle: Redox potential titration method
  • Measurement Range: 0 – 20 mg/L to 0 – 2000 mg/L (optional)
  • Repeatability: ≤±1% FS (for the 20 mg/L range)
  • Stability: ≤±3% FS/24 h
  • Output Signal: 4 – 20 mA/0 – 1 V
  • Communication Interface: Optional RS485/Modbus

8.2 Consumables List

Standard Consumables:

  • Printer ribbon (131F083)
  • Recording paper (131H404)
  • Silicone oil (XC885030)

Annual Consumables:

  • Pump diaphragm (125A114)
  • Control valve (126B831)
  • Activated carbon (136A075)

This guide comprehensively covers the operational key points of the Hach COD – 203 analyzer. In actual use, adjustments should be made based on specific water quality characteristics and site conditions. It is recommended to establish a complete equipment file to record each maintenance, calibration, and fault handling situation to ensure the long-term stable operation of the equipment.