How to choose a water quality sensor? PH、ORP、 Complete analysis of turbidity and dissolved oxygen parameters

Water quality monitoring is crucial in fields such as environmental protection, water management, aquaculture, and industrial wastewater treatment, and selecting appropriate sensors is key to ensuring data accuracy and system stability. This article will provide an in-depth analysis of the measurement principles, selection points, and typical application scenarios of the four core parameters of pH, ORP (oxidation-reduction potential), turbidity, and dissolved oxygen (DO), to help you make the best decisions.

1. pH sensor: precise monitoring of acidity and alkalinity

measuring principle

The pH sensor is based on the glass electrode method and determines the acidity or alkalinity of the solution (0-14 range) by measuring the activity of hydrogen ions.

Key factors for selection

✅  Accuracy: Laboratory grade (± 0.01pH) vs Industrial grade (± 0.1pH)

✅  Temperature compensation: Is automatic temperature compensation (ATC) function necessary?

✅  Electrode material:

• Glass electrode (universal type, suitable for most water quality)
• Antimony electrode (suitable for HF or high alkaline solutions)

• Solid state electrode (anti pollution, suitable for sewage)

Typical applications

Drinking water treatment (standard pH 6.5-8.5)

Wastewater treatment (anaerobic/aerobic process pH control)

Aquaculture (suitable pH 6.5-9.0 for fish)

2. ORP Sensor: Measurement of Redox Ability

measuring principle

ORP (Oxidation Reduction Potential) sensors measure the electron transfer ability (in mV) of a solution and are used to determine the oxidizing or reducing properties of water quality.

Key factors for selection

✅  Range: Generally -2000mV~+2000mV, chlorine disinfection system requires a higher range

✅  Electrode type:

Platinum electrode (high precision, suitable for laboratory use)

Gold electrode (resistant to hydrogen sulfide interference, suitable for wastewater treatment)

✅  Calibration method: Regular calibration with ORP standard solution (such as ZoBell solution) is required

Typical applications

Swimming pool disinfection (ORP>650mV indicates effective chlorine sterilization)

Industrial wastewater treatment (monitoring redox reaction efficiency)

Groundwater remediation (monitoring the degradation of reducing pollutants)

3. Turbidity sensor: detection of suspended solids in water

measuring principle

The turbidity sensor measures the concentration of particulate matter in water using optical scattering method (90 ° or 180 ° scattered light), with units of NTU (Nephelometric Turbidity Units).

Key factors for selection

✅  Range:

Low turbidity (0-10NTU, suitable for drinking water)

High turbidity (0-1000NTU, suitable for sewage)

✅  Light source type:

LED light source (low-cost, suitable for general monitoring)

Laser light source (high precision, suitable for low turbidity detection)

✅  Anti fouling design: Is it equipped with an automatic cleaning brush or air blowing?

Typical applications

Waterworks (effluent turbidity<1NTU)

River monitoring (sediment content change after rainstorm)

Beer/Beverage Production (Liquid Clarity Control)

4. Dissolved oxygen (DO) sensor: a key indicator of water oxygen content

measuring principle

Optical method (fluorescence method): Based on the quenching effect of oxygen molecules on fluorescence, the maintenance cost is low.

Polarography (Clark electrode): The electrolyte needs to be replaced regularly, but the response is faster.

Key factors for selection

✅  Measurement range: 0-20mg/L (conventional) vs 0-50mg/L (high oxygen environment)

✅  Response time: Optical method (about 15 seconds) vs Polarographic method (about 5 seconds)

✅  Applicable scenarios:

• Aquaculture (requires long-term stability, using optical methods)

• Wastewater treatment (requires rapid response, choose polarographic method)

Typical applications

Fish farming (DO>5mg/L to ensure survival rate)

Wastewater treatment (aerobic process with DO controlled at 2-4mg/L)

Environmental monitoring (ecological assessment of dissolved oxygen in lakes/oceans)

Comprehensive selection suggestions

6. Frequently Asked Questions and Answers

Q1: How to calibrate water quality sensors?

PH: Use pH 4.01/7.01/0.01 standard buffer solution

ORP: Use ZoBell or Light's Solution

Turbidity: Use Formazine standard solution

DO: Zero oxygen calibration (Na ₂ SO3 solution)+saturated oxygen calibration

Q2: How can the lifespan of sensors be extended?

Regular cleaning (especially for turbidity sensors)

Avoid prolonged dry storage (pH/ORP electrodes need to be soaked in storage solution)

Choose anti pollution coating (such as PTFE protective film)

Q3: How to choose wireless transmission?

4G/NB IoT (remote monitoring)

LoRa (low power consumption, suitable for areas without signal)

7. Conclusion

Choosing a suitable water quality sensor requires comprehensive consideration of measurement requirements, environmental adaptability, maintenance costs, and other factors. This article provides a detailed analysis of the principles and selection guidelines for the four major parameters of pH, ORP, turbidity, and dissolved oxygen, to help you optimize your water quality monitoring plan.

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