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TDS METER – CALIBRATION, TESTING & RESULT

Laboratory Testing Form – Engineers India Solutions
Test: Determination of Total Dissolved Solids (TDS) in Water
Field: Environmental Engineering / Water Quality Testing

1. Objective

To calibrate a Digital TDS Meter and determine the Total Dissolved Solids (TDS) concentration of a given water sample. TDS testing is an important water-quality test used for drinking water, groundwater, surface water, wastewater, industrial water, and environmental monitoring.

2. Principle

Total Dissolved Solids represent the concentration of dissolved substances present in water, including dissolved salts, minerals, and other ionic materials. A digital TDS meter generally estimates TDS from the electrical conductivity (EC) of the water and displays the result in mg/L or ppm.

Higher TDS indicates a greater concentration of dissolved substances, although TDS alone does not identify which substances are present.

3. Apparatus and Materials

• Digital TDS Meter

• Standard calibration solution

• Clean glass or plastic beaker

• Distilled/deionized water

• Water sample

• Tissue or lint-free paper

• Sample container

• Thermometer, where required

4. Calibration Procedure

1. Switch ON the digital TDS meter.

2. Check the electrode/sensor for cleanliness and physical damage.

3. Rinse the sensor with distilled or deionized water.

4. Gently remove excess water without damaging the sensor.

5. Pour a suitable quantity of standard TDS calibration solution into a clean beaker.

6. Immerse the TDS sensor in the calibration solution.

7. Ensure that the sensor is completely immersed according to the manufacturer's instructions.

8. Gently move the sensor to remove trapped air bubbles.

9. Allow the displayed value to stabilize.

10. Adjust the meter using its calibration function until the displayed value agrees with the certified value of the standard solution.

11. Remove and rinse the sensor with distilled water.

12. The instrument is now ready for sample testing.

5. Testing Procedure

1. Collect a representative water sample in a clean container.

2. Mix the sample gently to ensure uniformity.

3. Pour the required quantity into a clean beaker.

4. Rinse the TDS sensor with distilled water.

5. Immerse the sensor into the sample.

6. Avoid touching the sensor against the bottom or sides of the container.

7. Gently stir or move the sensor to eliminate air bubbles.

8. Wait until the digital display becomes stable.

9. Record the TDS value.

10. Repeat the measurement at least three times to check consistency.

11. Rinse the sensor after testing and store it according to the manufacturer's instructions.

6. Laboratory Observation

ParameterObservationInstrumentDigital TDS MeterCalibration Standard342 ppmCalibration

Reading342 ppmSample Temperature25°CTrial 1486 ppmTrial 2489 ppmTrial 3487 ppm

7. Calculation

Average TDS:

TDS = (486 + 489 + 487) / 3

Average TDS = 487.33 ppm

Therefore:

TDS ≈ 487 ppm

8. Test Result

The measured TDS of the tested water sample is approximately 487 ppm at the recorded test temperature.

The result should be interpreted according to the applicable water-quality requirements and the intended use of the water. TDS is an indicator of dissolved material concentration and should not be considered a complete assessment of water quality.

9. Precautions

• Calibrate the meter before testing.

• Use a clean and appropriate calibration solution.

• Do not contaminate the standard solution.

• Rinse the sensor between measurements.

• Remove air bubbles from the sensor.

• Wait for a stable reading before recording the result.

• Maintain consistent temperature where possible.

• Do not touch the sensing electrodes during measurement.

• Follow the manufacturer's calibration and storage instructions.

10. Conclusion

The digital TDS meter was successfully calibrated using a standard solution and subsequently used to test

the water sample. Three observations were recorded and the average TDS was calculated as approximately

487 ppm. Proper calibration, clean equipment, representative sampling, and careful observation are essential

for obtaining reliable laboratory testing results.

Note: The numerical readings shown above are illustrative laboratory observations. Actual laboratory or

field results should be entered in the testing form based on the instrument readings obtained during the test.

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Note-The ideal Total Dissolved Solids (TDS) level for drinking water is 150–250 ppm (parts per million), while a general safe range falls between 50 and 500 ppm