Definition
The Pen TDS Meter is a portable water quality detection instrument used to quickly determine the total dissolved solids content in aqueous solutions. Total dissolved solids refer to the total amount of soluble substances such as inorganic salts and organic matter dissolved in water, usually expressed in mass concentration in milligrams per liter or ppm. Named for its pen-like shape, this instrument is easy to operate and responsive, and is widely used in environmental monitoring, industrial production, agricultural irrigation, and water quality assessment in daily life.
Principle
The pen TDS meter works on the principle of conductivity measurement. Ions dissolved in water produce conductivity under the action of electric fields, and their conductivity is positively correlated with ion concentration. The instrument measures the conductivity of the solution through the electrode and converts the conductivity value into TDS value using a preset algorithm. The conversion formula is usually expressed as:TDS = k × EC, where EC is the measured value of conductivity and k is the conversion coefficient, and its value is related to the composition of the solution and temperature, and the common range is between 0.5 and 0.8.
Measurement method
When measuring, the power supply of the instrument should be turned on first, and the electrode should be submerged below the liquid level to be measured to avoid contact with the container wall. Read the results after the values stabilize. In order to ensure the accuracy of measurement, it is necessary to calibrate with a standard solution before use, and the calibration frequency is determined according to the use environment. The electrode should be kept clean during the measurement process to avoid bubble adhesion. For samples with different temperatures, some instruments have automatic temperature compensation to correct the effect of temperature on conductivity.
Influencing factors
Measurement results are influenced by a variety of factors. Changes in solution temperature can alter ion mobility rates, leading to fluctuations in conductivity. Different types of ions in water will affect the conversion coefficient, for example, there is a difference in the conversion coefficient between sodium chloride solution and calcium carbonate solution. Contamination or aging of the electrodes can cause a decrease in response sensitivity. In addition, although suspended particulate matter in water samples is not a dissolved solid, it may interfere with the measurement if it is deposited on the electrode surface. The calibration status of the instrument and the operational standardization of the measurement will also affect the reliability of the results.
Applications
In the field of drinking water treatment, the instrument can be used to monitor the quality of effluent from purification equipment. Used in aquaculture to control mineral concentrations in water bodies. Guiding water quality suitability assessment in agricultural irrigation. Water monitoring for processes such as electroplating and pharmaceuticals in industrial production. Laboratories are used for routine water quality screening. Simple testing of drinking water and water purifier effluent can be carried out in the home. These applications are based on the rapid acquisition of water quality parameters to provide reference for subsequent decision-making.
Key points of selection
When selecting the sample, it is necessary to consider whether the measurement range covers the concentration of the sample to be tested. The resolution should meet the detection requirements, and the common instrument resolution is 1 milligram per liter. Automatic temperature compensation helps improve measurement consistency. The calibration method should be a simple and reliable design. The protection level of the instrument needs to be adapted to the use environment, such as splash-proof design for outdoor use. Battery life and ease of electrode replacement are also considerations for long-term use. Users should balance functional requirements and usage costs based on actual application scenarios.