Introduction:
pH sensors (acidity and alkalinity sensors) and DO sensors (dissolved oxygen sensors) are core water quality monitoring devices in industrial processes and laboratories. They are used to accurately measure the acidity and alkalinity (pH value) and dissolved oxygen concentration of liquid media, respectively, and are widely used in industries that are sensitive to water quality parameters, such as pharmaceuticals, bioengineering, food, environmental protection, and aquaculture.
I. pH Sensor (Acidity/Alkalinity Sensor)
Core Structure and Working Principle
The core components include a glass electrode (sensing electrode), a reference electrode, a temperature-compensating electrode, and an electrode sheath (some models include a flow cell).
When the glass electrode comes into contact with the liquid being measured, a potential difference is generated based on the hydrogen ion concentration in the medium. The reference electrode provides a stable reference potential, and the potential difference between the two electrodes follows the Nernst equation relationship with the pH value.
The temperature-compensating electrode corrects for the influence of ambient temperature on the measurement in real time, ensuring measurement accuracy over a wide temperature range. Finally, the potential signal is converted into a pH value output in the range of 0-14 via a transmitter.
Core features and advantages
High measurement accuracy: Accuracy up to ±0.01~±0.05PH, fast response speed (typically ≤3 seconds), capable of capturing pH changes in real time.
Diverse media compatibility: Resistant to acid and alkali corrosion; electrode materials include glass and PTFE coating; suitable for pure water, acid and alkali solutions, fermentation broth, food and beverages, and many other media.
Strong environmental adaptability: Wide measurement temperature range (0~100℃); some sanitary models support high-temperature sterilization (121℃); withstands certain pressures (typically ≤1MPa).
Functional expandability: Supports online calibration and self-diagnosis; some models include cleaning functions (such as ultrasonic cleaning) to reduce the impact of scaling on measurements.
Main types and applicable scenarios
Immersion pH Sensors: Directly immersed in containers such as storage tanks and reaction vessels, suitable for monitoring static or semi-dynamic media (e.g., fermenters, wastewater tanks).
Flow-through pH Sensors: Connected to pipelines via a flow-through tank, suitable for continuous flow media (e.g., pharmaceutical dispensing pipelines, food production lines).
Sanitary pH Sensors: Featuring a 316L stainless steel sheath and a dead-angle-free design, supporting in-line cleaning (WIP) and in-line sterilization (SIP), compliant with GMP and FDA standards, suitable for the pharmaceutical, vaccine, and dairy industries.
Industrial Corrosion-Resistant pH Sensors: Electrodes protected with PTFE or Hastelloy, suitable for highly corrosive media (e.g., chemical acid and alkali solutions, desulfurization wastewater).
II. DO Sensor (Dissolved Oxygen Sensor)
Core Structure and Working Principle
The mainstream types are polarographic (including silver-gold electrodes, electrolytes, and a breathable membrane) and fluorescence (including a fluorescent cap, LED light source, and photodetector).
Polarographic: A constant voltage is applied between the electrodes. Dissolved oxygen permeates through the breathable membrane and undergoes an electrochemical reaction on the electrode surface, generating a current signal proportional to the oxygen concentration.
Fluorescence: The fluorescent cap is excited by an LED light source to produce fluorescence. Dissolved oxygen reacts with the fluorescent substance, causing fluorescence quenching. The degree of quenching is related to the oxygen concentration. The signal is captured by a photodetector and converted into a dissolved oxygen value (unit: mg/L or % air saturation).
Core features and advantages
Precise and Stable Measurement: Fluorescence sensors require no polarization and have no consumable electrodes, achieving an accuracy of ±0.01 mg/L with minimal drift; polarographic sensors are also cost-effective, meeting the needs of conventional industrial applications.
Adaptable to Complex Operating Conditions: Resistant to temperature (0~80℃) and pressure (≤1.6MPa) variations, with breathable membrane materials available in PTFE and silicone rubber, suitable for media such as pure water, fermentation broth, wastewater, and seawater.
Easy Maintenance: Fluorescence sensors require no frequent calibration or electrolyte replacement and have a long service life (fluorescent cap lifespan is typically 1-2 years); polarographic sensors have low maintenance costs and easy component replacement.
Hygiene Standards Meet Standards: Hygienic models support high-temperature sterilization, with a seamless structure, meeting the cleanliness requirements of the bio-fermentation and pharmaceutical industries.
Main types and applicable scenarios
Immersion DO Sensors: Directly immersed in fermenters, aquaculture ponds, etc., suitable for biological culture and aquaculture applications.
Flow-through DO Sensors: Connected to pipelines via a flow-through tank, suitable for continuous production processes (such as aseptic pharmaceutical preparation and food and beverage production lines).
Sanitary DO Sensors: Support SIP sterilization (121℃), materials meet FDA standards, suitable for aseptic applications such as vaccine production and cell culture.
Industrial Wastewater DO Sensors: High protection rating (IP68), strong anti-fouling capability, suitable for harsh environments such as wastewater treatment, desulfurization, and denitrification.
Typical application industries
Pharmaceutical/Vaccine Industry: Online monitoring of pH/DO in aseptic solution preparation and fermentation tanks to ensure stable reaction conditions and compliance with GMP data traceability requirements.
Biotechnology Industry: Monitoring of cell culture and microbial fermentation processes to ensure the efficiency and purity of bioactive substance production.
Food/Dairy Industry: Water quality monitoring in beverage preparation and yogurt fermentation to prevent abnormal pH values from affecting product flavor and shelf life.
Environmental Protection Industry: Monitoring of aeration tanks and effluent quality in wastewater treatment plants to ensure that treated water meets discharge standards.
Aquaculture Industry: Real-time monitoring of dissolved oxygen in aquaculture ponds to prevent fish and shrimp from dying due to oxygen deficiency and improve survival rates.
