Definition
The Total Dissolved Solids Test Pen, often referred to simply as the TDS Test Pen, is a portable electronic instrument used to quickly measure the total dissolved solids content in liquids. Total dissolved solids refers to the total amount of inorganic salts and small amounts of organic matter dissolved in water, usually expressed in mass concentrations in milligrams per liter or ppm. This instrument is widely used in water quality assessment, production process monitoring, and other fields, providing users with instant dissolved solids content reference data.
Principle
The TDS test pen works based on the conductivity measurement principle. Ionized solid matter dissolved in water increases the conductivity of water. The instrument measures the conductivity value of the solution by applying an AC voltage between the electrodes, which is then converted into the total dissolved solids concentration value by a built-in algorithm. The basic conversion relationship can be expressed as: TDS = k × EC, where EC is the measured conductivity value and k is the conversion coefficient, usually in the range of 0.5 to 0.8, depending on the ionic composition properties of the dissolved solid.
Measurement method
When measuring with a TDS test pen, the instrument is first calibrated with a standard calibration solution to ensure measurement accuracy. During the measurement process, the electrode should be completely immersed in the liquid to be measured to avoid air bubble interference. After the reading stabilizes, the value is recorded and displayed. Clean the electrode with deionized water before and after each measurement to prevent cross-contamination. For samples at different temperatures, some instruments have automatic temperature compensation to correct readings to values at standard reference temperatures.
Influencing factors
Measurement results are influenced by a variety of factors. Changes in solution temperature can change ion mobility, which can affect conductivity measurements. The chemical composition of the dissolved solid determines the conversion relationship between conductivity and TDS, and different ion combinations have different conductive properties. Contaminated or aging of the electrodes can lead to measurement deviations and require regular maintenance calibration. In addition, air bubbles in the sample, the material of the measuring vessel, and external electromagnetic interference can also affect the measurement accuracy.
Applications
In the water treatment industry, this instrument is used to monitor the effluent quality of reverse osmosis systems and evaluate the efficiency of filter elements. It is commonly used in the field of drinking water testing to quickly assess water quality. It is used in aquaculture to monitor the mineral content of water bodies and maintain a suitable breeding environment. It can be used as a preliminary screening tool in the laboratory and combined with other analytical methods to complete comprehensive water quality assessment. The food and beverage industry is used for production water quality monitoring to ensure that product water meets process requirements.
Selection reference
The selection of the right TDS test pen should consider whether the measurement range covers the actual application requirements, with common instruments ranging from 0 to 9990 mg/L. The measurement resolution should meet the monitoring requirements, typically up to 1 mg per liter. The automatic temperature compensation function helps reduce temperature-induced measurement errors. The instrument calibration method should be simple and reliable, and models that support multi-point calibration can improve measurement accuracy. In addition, practical usage requirements such as electrode material durability, power supply method, and data storage function need to be considered.