1. Working principle background
Capacitance value depends on the dielectric constant of the medium:
- Pure water has an extremely high dielectric constant (~80), while air is only ~1. This large difference creates an obvious capacitance signal, which theoretically makes pure water an easy medium for capacitive measurement.
- However, ultra-pure/deionized water has extremely low conductivity, which brings unique measurement limitations compared with ordinary tap water.
2. Two mainstream types & their suitability
(1) RF admittance (radio frequency capacitive) level gauge — Recommended for pure water
It eliminates the interference of medium conductivity, adhesion and stray capacitance.
- Suitable for deionized water, distilled water, ultra-pure water in power plants, semiconductor factories, pharmaceutical purified water systems;
- Works stably even with thin water film adhesion on probes, no signal drift.
(2) Ordinary simple capacitive level switch (low-cost model) — Not ideal for ultra-pure water
Common cheap capacitive probes rely on liquid conductivity to form a loop. Pure water barely conducts electricity, which may cause:
- Unstable signal, failure to trigger liquid level signal;
- Large measurement error or no response at all for continuous level measurement.
3. Key application scenarios for pure water measurement
- Power plant boiler pure water tank, condensate tank;
- Electronic factory ultra-pure water storage and circulation tanks;
- Pharmaceutical purified water, injection water storage vessels;
- Laboratory distilled water equipment, pure water preparation stations.
4. Selection & installation tips
- Choose RF admittance capacitive type instead of basic conductive capacitive probes for deionized/ultra-pure water;
- Select 316L stainless steel or PTFE coated probes to meet sanitary requirements;
- Avoid long-term air-water boundary scaling on the probe surface; regular cleaning ensures stable readings;
- For continuous liquid level monitoring (4-20mA output), high-precision RF capacitive transmitters are preferred.
Brief conclusion
Ordinary capacitive probes may fail on ultra-pure water, but RF admittance capacitive level gauges perform perfectly for pure water level measurement, and are widely used in pure water treatment industries.
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