In the concentration control process of industrial production, online concentration meters are the core equipment to ensure process stability, safety, and cost optimization. Among them, conductivity method and refractive concentration meter, as two mainstream technical solutions, can both achieve real-time detection. However, due to differences in core principles and technical characteristics, they show significant differences in applicable scenarios, accuracy performance, and operation and maintenance costs, and need to be scientifically selected based on actual production needs. Here is a detailed introduction:

1、 Measurement principle and applicable medium: the root cause of core differences

The conductivity method concentration meter (such as the Shanghai Xuantian SJT-6000A equipment) converts concentration based on the conductivity of electrolyte ions in the solution, and is only suitable for strong electrolyte solutions (such as NaOH, hydrochloric acid, potassium hydroxide, nitric acid, sulfuric acid and other acid-base salt solutions). The higher the ion concentration, the stronger the conductivity, and the concentration conversion is direct and efficient. However, it cannot measure non electrolyte solutions such as alcohol and glycerol, nor is it suitable for high-purity non-ionic media.

Refractive concentration meters (such as the Shanghai Xuantian SJT-6000Z equipment) rely on the principle of critical angle total reflection of light, and complete the conversion through the linear relationship between refractive index and concentration, without being limited by "electrolyte". As long as there is a clear correspondence between the refractive index of the medium and concentration, it can be measured. It is suitable for electrolyte solutions such as NaOH, hydrochloric acid, potassium hydroxide, nitric acid, sulfuric acid and other acid-base salt solutions, as well as precise detection of non electrolyte solutions such as ethanol, ethylene glycol, sugar solution, etc., with a wider range of applicable media.

2、 Accuracy and anti-interference: key to industrial working condition adaptation

The conductivity method concentration meter has a moderate measurement accuracy with a concentration error of about ± 2.0% FS, and requires dynamic compensation with a PT1000 temperature sensor - temperature changes can significantly affect ion activity and interfere with measurement results. At the same time, other impurity ions in the solution (such as salts in wastewater treatment) can easily lead to the phenomenon of "false conductivity", causing concentration misjudgment. Suspended particles may also adhere to the electrode surface, affecting measurement stability. Its response speed is fast, usually ≤ 1 second, which can meet the real-time monitoring requirements of conventional working conditions.

Refractive concentration meters have higher optical measurement accuracy, with a concentration error of only ± 0.1% FS (such as the Shanghai Xuantian SJT-6000Z equipment), and more outstanding anti-interference ability. Only sensitive to the refractive index of the medium, unaffected by color, bubbles, and suspended particles (such as stable measurement of hydrochloric acid solutions containing impurities in the chlor alkali industry), with a wider temperature compensation range (-20 ℃~100 ℃) and more accurate error control. Better response speed, ≤ 1 second, suitable for high-precision and fast response process control scenarios (such as electronic grade hydrochloric acid purification).

3、 Maintenance and Cost: Core Considerations for Long Term Use

The maintenance cost of the conductivity method concentration meter is lower, with no consumption of reagents or consumables. The electrode core has a lifespan of 1-3 years, and only requires cleaning of the electrode surface for scale or attachments every 2-4 weeks. Calibration operation is simple, supports one click completion, does not require professional technical personnel, suitable for scenarios with limited budget and relatively simple working conditions, and long-term operation and maintenance costs are controllable. The electrode needs to be made of polyethylene terephthalate PP、 Tetrafluoroethylene and other corrosion-resistant materials are suitable for contact with strong acidic and alkaline media.

The initial procurement cost of a refractive concentration meter is slightly higher, but the long-term maintenance cost is controllable. The core component sapphire prism is wear-resistant and corrosion-resistant, with a lifespan of over 5 years and no reagent consumption. It only needs to be wiped clean of oil stains or attachments on the prism surface every 1-3 months to avoid affecting transparency. Sapphire should be used for the contact medium part PFA、 Dual phase steel and other corrosion-resistant materials are suitable for complex working conditions such as strong corrosion and high purity, and the overall maintenance difficulty is relatively low.

4、 Applicable scenarios and ranges: core selection criteria

The conductivity method concentration meter is suitable for a medium concentration range (such as low concentration NaOH 0.01% -16%, high concentration NaOH 25% -50%), and is more suitable for routine concentration monitoring of electrolyte solutions, such as neutralization of ordinary NaOH wastewater and conventional hydrochloric acid pickling processes. This type of scenario does not require high accuracy (± 0.5% error is acceptable), has good medium purity, few impurity ions, and pursues low-cost operation and maintenance.

Refractive concentration meters are suitable for a wider concentration range (such as 0-90% hydrochloric acid and 0-100% organic solvents) and are more adaptable to complex scenarios. It is suitable for non electrolyte solution measurement (such as ethanol concentration monitoring), high-precision control requirements (such as electronic grade hydrochloric acid purity detection), and can also cope with harsh working conditions containing bubbles, suspended particles, and strong corrosion (such as hydrochloric acid concentration monitoring in chlor alkali industrial synthesis furnaces). Especially suitable for process links that require high measurement accuracy and complex medium composition.

5、 Selection Summary

If the measuring object is an electrolyte solution (such as ordinary acid and alkali), the working condition is simple without excessive impurities, the accuracy requirements are average, and low-cost operation and maintenance are pursued, the Shanghai Xuantian SJT-6000A conductivity concentration meter is preferred; If you need to measure non electrolyte/complex electrolyte solutions, require high-precision anti-interference, face harsh working conditions (including impurities and strong corrosion), or require wide range coverage, a refractive concentration meter is a better choice. The core difference between the two is essentially the difference in technical paths between "ion conductivity dependence" and "optical property dependence", which requires comprehensive selection based on medium type, accuracy requirements, and operating conditions.