Definition
A total dissolved solids meter, commonly known as a TDS water quality meter, is a portable or online detection device used to determine the total dissolved solids content in water. Total dissolved solids refers to the total amount of inorganic salts, organic matter and some soluble particles dissolved in water, usually expressed in terms of mass concentration per milligram per liter. This instrument is widely used in environmental monitoring, industrial production, agricultural irrigation, and daily water quality assessment, providing key data support for water quality management.
Principle
TDS water quality measuring instrument mainly works on the principle of conductivity measurement. Since the ions dissolved in water are electrically conductive, the instrument indirectly estimates the total dissolved solids content by measuring the conductivity of the aqueous solution. The core relationship can be expressed as: TDS ≈ k × EC, where EC is the conductivity value and k is the conversion coefficient, usually between 0.55 and 0.8, depending on the ionic composition of the dissolved solid in the water. The instrument has a built-in temperature sensor for automatic temperature compensation to eliminate the effect of temperature on conductivity measurements.
Measurement method
The standard measurement process includes three steps: instrument calibration, sample preparation, and data reading. First, the instrument needs to be calibrated using a standard conductivity solution to ensure accurate measurement references. When preparing the sample, it is necessary to ensure that the water sample to be tested is fully mixed and free of bubbles, and the measuring probe should be completely submerged below the liquid level. Readings should be recorded after the values have stabilized, and most instruments offer real-time display capabilities. For different application scenarios, the appropriate measurement mode can be selected according to relevant standards such as GB/T 5750.4 or ISO 7888.
Influencing factors
The accuracy of the measurement results is influenced by several factors. Water temperature changes the ion mobility, and although modern instruments have temperature compensation functions, they still need to be calibrated under extreme temperature conditions. The type and proportion of ions in water will affect the conversion relationship between conductivity and total dissolved solids, and a specific conversion factor should be used for water samples with special compositions. Contamination of the probe or aging of the electrodes can lead to a decrease in response sensitivity and require regular cleaning and maintenance. In addition, air bubbles, suspended particles, and the material of the measurement container in the water sample can also introduce interference.
Applications
In the field of drinking water treatment, the instrument is used to monitor the efficiency of purification equipment and changes in water quality in the pipe network. It is used in aquaculture to maintain the appropriate mineral concentration in water. In terms of agricultural irrigation, the selection of irrigation water is guided according to the water quality grading standards. In industrial production, boiler water, cooling circulating water, and ultrapure water preparation in the electronics industry all need to continuously monitor total dissolved solids. It is often used in laboratories as a preliminary screening tool for water quality, in conjunction with more precise analytical methods.
Selection reference
When choosing an instrument, the measurement range, accuracy level, functional configuration and actual needs should be comprehensively considered. Basic models typically cover the range of 0 to 2000 mg/litre, and professional models can be scaled to higher concentrations. In terms of accuracy, models with an error of less than ±2% can be selected for conventional applications, while higher precision is required for scientific applications. In terms of function, practical features such as automatic temperature compensation, data storage, and multi-point calibration should be paid attention to. The use environment determines the requirements of the protection level of the instrument, and products with corresponding protective shells should be selected outdoors or industrial sites. The user-friendly design of the user interface and the ease of subsequent maintenance should also be taken into account.