Definition
A pen dissolved oxygen tester is a portable water quality analysis instrument used to quickly determine the concentration of dissolved oxygen in water in the field. Dissolved oxygen refers to molecular oxygen dissolved in water, and its content is a key parameter for evaluating water self-purification capacity, ecological environment health, and industrial process control. The instrument usually adopts an integrated design, resembling a pen, with digital display and data storage functions, suitable for real-time measurement in various scenarios such as field surveys, aquaculture, environmental monitoring, and industrial water treatment.
Principle
The mainstream pen dissolved oxygen tester works based on the electrochemical principle of polar spectroscopy or galvanic cell method. The sensor core consists of a cathode, anode, and electrolyte, and is covered with a breathable membrane on the outside. Dissolved oxygen diffuses into the sensor through the thin film, where a reduction reaction occurs at the cathode, producing a diffusion current or potential signal proportional to the oxygen concentration. The instrument's internal circuitry converts this signal into a dissolved oxygen concentration value, typically in milligrams per liter or percentage saturation. Its basic relationship can be expressed as: I = k · C, where I is the sensor output current, k is the instrument constant, and C is the dissolved oxygen concentration.
Measurement method
When measuring with a pen dissolved oxygen tester, you need to follow a standardized operating procedure. Instrument calibration is performed first, usually one or two points in air-saturated water or zero-oxygen solution. Dip the sensor probe into the water sample to be measured while measuring, ensuring that the probe is completely submerged and avoid bubble attachment, maintaining proper agitation to allow water to flow through the membrane surface. Record the value after the reading is stable. After measurement, the probe should be cleaned with deionized water and the electrolyte and breathable membrane should be replaced regularly as recommended by the manufacturer to maintain sensor performance.
Influencing factors
Measurement accuracy is influenced by various factors. Temperature changes will affect the solubility of oxygen in water and the reaction rate of the sensor, and modern instruments often integrate temperature sensors for automatic compensation. The change of water salinity will change the dissolution characteristics of oxygen, and the compensation factor should be set according to the actual salinity. The velocity of the water flow affects the diffusion of oxygen to the surface of the membrane, and moderate agitation can obtain stable readings. Sensor condition is a critical factor, and membrane breakage, electrolyte contamination, or electrode aging can all contribute to biased readings. In addition, changes in atmospheric pressure can affect oxygen saturation calculations, and some instruments provide barometric pressure compensation.
Applications
Pen dissolved oxygen testers have a wide range of uses in the field of water quality monitoring. It is used in environmental monitoring to assess the eutrophication status and ecological health of rivers, lakes and oceans. It is used in aquaculture to monitor the level of dissolved oxygen in the aquaculture pond and prevent fish from dying due to lack of oxygen. Wastewater treatment plants are used to optimize the aeration process and control the biochemical treatment efficiency. The food and beverage industry is used to monitor the quality of production water. It is used in field experiments and classroom demonstrations in scientific research and education. Its portability makes it a powerful tool for rapid on-site screening, often complementing large analytical instruments in the laboratory.
Selection considerations
When choosing a pen dissolved oxygen tester, technical parameters and actual needs should be comprehensively considered. The measurement range needs to cover the intended application scenario, with common instruments ranging from 0 to 20 mg/L. The resolution and accuracy should meet the requirements of relevant industry standards. The instrument should have automatic temperature compensation function, and the salinity and air pressure compensation capacity should be selected according to the application environment. The protection level needs to adapt to the use environment, and it is recommended to choose a waterproof design for outdoor applications. The user interface should be intuitive and easy to use, and data storage and transmission functions can improve work efficiency. Maintenance costs involve sensor consumables replacement cycles and costs, which need to be taken into account in long-term use. The ease of instrument calibration is also one of the factors that affect the user experience.