Measurement of TDS (Total Dissolved Solids) in field and laboratory conditions is based on measuring the electrical conductivity and converting it to ppm using a conversion factor.

Practical procedure:

• Calibrate the device according to the instructions.
• Rinse the electrode with distilled water.
• Immerse the electrode to the recommended depth so that the sensors are fully covered.
• Remove air bubbles and keep the sample still until the reading stabilizes (usually 10–30 seconds).

Record the temperature at the time of measurement — it affects conductivity and requires compensation.

Calibration is critically important:

• Use factory standard conductivity solutions (common standards ≈84 µS/cm, 1413 µS/cm, 12,880 µS/cm) or ready-made TDS standards.
• For higher accuracy, a two-point or three-point calibration within the expected range is recommended.
• Check calibration before a series of measurements and after any mechanical impact on the device.

Conversion to TDS:

TDS (ppm)=κ(μS/cm)×CF\text{TDS (ppm)} = \kappa (\mu S/cm) \times CFTDS (ppm)=κ(μS/cm)×CF

where κ is the measured conductivity and CF is the conversion factor.
Typical CF for portable devices is 0.5 (default) or 0.64; depending on the ionic composition of the solution, CF can vary approximately 0.45–0.8.
Example: κ = 500 µS/cm, CF = 0.5 → TDS = 500 × 0.5 = 250 ppm.

Sensor types:

• Simple two-pole electrodes are cheaper but sensitive to polarization and lose stability at high concentrations.
• Four-pole electrodes (Kelvin method) provide more stable readings over wide ranges and are less affected by electrode contact with the solution.

Errors and sources of instability:

• Incorrect calibration, dirty or dried electrodes, air bubbles, sample inhomogeneity, high proportion of nonionic substances, rapid temperature changes.
• Typical error of handheld TDS meters is ±2–5%, resolution often 1 ppm.

Protocol recommendations:

• Calibrate before a series of measurements.
• Perform at least three repetitions and take the average.
• Record the temperature and the CF used.
• Clean the sensor according to the manufacturer’s instructions and store it in the recommended solution.
• For critical or regulatory applications, use laboratory methods with full analytical breakdown and traceable standards.