In industrial slurry concentration measurement, the microwave method and the optical turbidity method are often compared. The former measures the total solids content TS of all solids in the pipeline, while the latter measures the turbidity/SS of micron-level suspended fine particles in water. Their principles, measuring ranges, and applicable operating conditions differ significantly, so the characteristics of the process medium must be clarified before selection.
I. Core Difference: Total Solids Content vs. Suspended Turbidity
In one sentence: the microwave method measures total solids content, while the optical turbidity method measures the turbidity of suspended fine particles. Microwaves penetrate the entire pipeline section and are not affected by color, light transmittance, or bubbles; optical probes rely on the light path, and high-solids viscous slurries directly obscure the window. Therefore, for high-solids scenarios such as desulfurization gypsum slurry and red mud underflow, microwave is preferred; for low-turbidity scenarios such as clear water outlet, CUS optical sensors can be selected.
II. Comparison of Underlying Measurement Principles
1. Microwave Method (Dielectric Constant Transmission Method, Measuring Total Solids Content TS)
The dielectric constant of pure water is ε≈80, while that of inorganic solid particles is only 2~8, a very large difference. Microwaves penetrate the entire pipeline medium, detecting signal attenuation and phase shift, and convert the overall dielectric properties of the medium into mass/volume total solids content (% TS, g/L).
- Measurement object: the total proportion of all solid phases, including settled large particles, sludge, gypsum slurry, and red mud, without distinguishing particle size.
- Signal carrier: microwave electromagnetic waves, unaffected by light transmittance, color, or scattering by tiny suspended particles.
- Installation form: pipeline through-type, with antennas outside the pipe wall, not immersed in the medium, and no probe contacting the slurry.
2. CUS Series (Infrared Optical Turbidity Method, Measuring Suspended Turbidity/SS)
CUS50D, CUS51D, and CUS52D all use infrared optical principles and can only sense micron-level suspended fine particles. Large settled particles and viscous slurry completely obscure the light path, causing data failure.
- CUS50D: transmission absorption principle. An infrared beam passes through the medium; particles absorb and block the light, and turbidity and SS are calculated from light attenuation; suitable for medium-to-high-solids dark sludge, with a 5/10 mm optical path single-point transmission window.
- CUS51D: 90°/135° multi-beam scattered light. Complies with ISO turbidity standards; light scatters when it hits tiny suspended particles, and turbidity is calculated from the received scattered light intensity; dedicated to municipal wastewater and aeration tank SS, capable of measuring 0~300 g/L sludge.
- CUS52D: standard 90° scattered light. Complies with ISO7027, laboratory-grade low-turbidity measurement, only suitable for clear water and low-SS outlet scenarios, measuring range 0~4000 FNU, with precise detection of trace fine particles.
Common feature: all are immersed probes, with the optical glass window directly immersed in water; they generate scattering/absorption signals only for micron-level suspended fine particles. The output is turbidity FNU/NTU and suspended SS (only suspended fine particles), which is different from the definition of total solids content in the pipeline.
III. Measuring Range and Applicable Solids Content Interval
| Solution | Applicable Solids Content | Adapted Medium |
|---|---|---|
| Microwave transmission analyzer | 0~50%TS (0~500 g/L) | High-solids viscous slurries: desulfurization gypsum slurry, red mud, sludge dewatering feed, high-concentration lime milk; can also measure completely opaque media |
| CUS50D transmission optical | 0~60 g/L (up to 6% TS) | Medium sludge and industrial wastewater; above 6% solids content the light path is completely obscured, and readings saturate and become distorted |
| CUS51D scattered optical | 0~30 g/L (optimal within 3% TS) | Aeration tanks and biochemical tank return sludge; high-solids slurry easily saturates |
| CUS52D scattered optical | 0~4 g/L (within 0.4% TS) | Tap water, clear outlet water, low-turbidity filtrate; high-solids media cannot be measured directly |
IV. Comparison of Interference Resistance (Key for Desulfurization/Incineration Scrubber Conditions)
1. Bubble and Foam Interference
- Microwave: bubbles have a dielectric constant close to air and have very little effect on microwave signals; scrubber circulating water with foam has low error.
- CUS optical: bubbles strongly scatter infrared light, and foam covering the probe window directly causes data drift and falsely high values, requiring continuous purge cleaning.
2. Medium Color and Dark Slurry
- Microwave: completely unaffected by black, red, or yellow media; red mud and dark desulfurization gypsum slurry can be measured stably.
- CUS optical: dark dyes and high-color wastewater absorb a large amount of infrared light, resulting in low readings and requiring frequent calibration.
3. Scaling, Crystallization, and Viscous Coating
- Microwave: the pipeline has a polished PFA lining and no inserted probe; scaling only attaches to the pipe wall and has little effect on through-type microwaves, with a maintenance cycle of 3~6 months.
- CUS series: the optical window is directly immersed; alkaline scale, gypsum crystals, and viscous sludge can easily blind the glass window, requiring compressed air purge cleaning weekly or even daily, resulting in high maintenance.
4. Salinity and Conductivity Fluctuations
- Microwave: built-in temperature + dielectric dual compensation; high-salinity scrubber circulating water drifts only slightly, and the algorithm automatically corrects it.
- CUS optical: salinity does not directly interfere with the optical signal, but high salinity accelerates crystallization and scaling, indirectly causing probe contamination.
V. Structure, Corrosion Resistance, and Explosion-Proof Adaptation
Microwave Teqwave MW500
- Integrated pipeline design, PFA lining for full corrosion resistance, FFKM seals, suitable for concentrated acids and alkalis.
- No immersed probe, no wear, and no particle erosion scratching the optical window.
- Supports Ex ia IIC T6 intrinsically safe explosion protection; installation starts from pipeline DN80.
- Disadvantages: cannot be installed in small pipe diameters DN50 and below; equipment procurement cost is higher.
CUS50D/CUS51D/CUS52D Immersed Probes
- The sensor head is PCTFE/316Ti and can withstand acids and alkalis, but the front optical glass directly faces slurry erosion.
- Must be equipped with a retractable bracket and purge device; otherwise crystallization quickly blinds the window.
- Explosion-proof versions require an explosion-proof protective sheath; explosion-proof wiring for remote probe cables is cumbersome.
- Advantages: can be used in small flow channels, DN50 small pipe bypasses, and shallow tank immersion installation; unit price is lower.
VI. Differences in Output Index Definitions
Microwave output: total solids content TS (mass percentage %, g/L), representing the true proportion of all solids (suspended + settled large particles) in the pipeline fluid, used for dosing, sludge discharge, and dewatering interlock control, and meeting process slurry concentration control requirements (core control parameters for desulfurization gypsum and red mud).
CUS optical output: turbidity FNU/suspended SS (only suspended fine particles), reflecting only micron-level floating fine particles in water; large settled particles at the bottom of the pipeline do not participate in the measurement at all. The value ≠ total slurry concentration and is only suitable for clear outlet water and low-solids monitoring in biochemical tanks.
Key distinction: for high-solids gypsum slurry in desulfurization tower underflow, the CUS probe directly saturates and has no reading; microwave can stably read the true solids content.
VII. Quick Differentiation of the Three CUS Models
- CUS52D: dedicated to low-turbidity clear water (tap water, filtered outlet water), completely unsuitable for high-solids scrubber circulating liquid.
- CUS51D: municipal wastewater biochemical tanks and return sludge (≤3% solids content), medium-to-low-solids dilute slurry.
- CUS50D: industrial wastewater and medium-concentration sludge (≤6% solids content), can be used short-term for dilute scrubber circulating water; high-solids gypsum slurry will saturate and fail.
VIII. Selection Recommendations and Summary
Scenarios for Choosing the Microwave Method (Teqwave MW500)
Desulfurization gypsum discharge slurry, red mud thickener underflow, lime milk feed, sludge dewatering inlet and outlet (solids content >6%, viscous and opaque, high foam, prone to crystallization). Requires precise total solids content interlock dosing and sludge discharge, long-term maintenance-free operation, and explosion-proof compliance.
Scenarios for Choosing CUS Optical Sensors
Only scrubber clear water outlet and filtrate monitoring (low turbidity, solids content <3%), where only trace suspended impurities need to be monitored. Limited budget, small pipe bypass installation, and acceptable high-frequency purge maintenance.
Summary: the microwave method measures the true concentration of all solids in the entire pipeline (total solids content) and is not afraid of high solids, foam, or dark slurry; CUS50/51/52D are optical turbidity probes that only measure floating fine particles in water. High-solids viscous slurry easily blocks and saturates the light path, so they are only suitable for low-concentration clear water/dilute wastewater.
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