The HY551-B UV254 COD sensor offers one-point or two-point calibration in mg/L. One-point calibration is performed in distilled water and a 150 solution, while two-point calibration is conducted in distilled water, a 150 solution, and a 450 solution.

Instruments and materials required for COD calibration

1. KHP (Potassium hydrogen phthalate, C8H5KO4)

2. Distilled water or deionized water (Watson's distilled water)

3. Beaker

4. Gloves

5. Stirring rod

6. Air pump

Preparation Before Calibration

Accurately weigh 1.2754 g of KHP and place it in a 1000 mL flask. Fill with distilled or deionized water up to the mark. This solution contains a 1500 mg/L COD stock solution (it can also be purchased directly from Yushan Sensor Manufacturer).

(2) Transfer 100 mL of COD stock solution into a 1000 mL volumetric flask, then fill to the mark with distilled or deionized water. Mix thoroughly to ensure a COD concentration of 150 mg/L.

(3) Store this concentrated standard solution in a black glass bottle and keep it refrigerated to prevent decomposition. The diluted standard solution must be used within 24 hours after preparation.

HY551-B UV254 COD Sensor Calibration (2-Point Calibration)

Restore user calibration data to default: K=1, B=0.

(2) Place the sensor in pure water (distilled or deionized water) and ensure all optical paths are submerged more than 2cm below the surface with no bubbles. Note: Do not use tap water. Then read the COD value, e.g., COD=0.2mg/L, and record it as X.

(3) Place the sensor in a 150mg/L COD solution and repeat step 3.2, recording the value as Y.

(4) Record the values of K and B as follows: K = 150 / (Y - X), B = -KX

(5) Write the K and B values into the sensor.