Some liquids fight back
Level sensing in difficult liquids means measuring level reliably when the liquid foams, clings, carries solids, corrodes or conducts. Floats stick and ultrasonic signals can be confused by foam and vapour. Gill capacitive level sensors have no moving parts, and LevelSlick is designed specifically for challenging conductive liquids.
How do you measure level in a difficult liquid?
Level in a difficult liquid is measured with a sensor chosen for the liquid first and the tank second. Foam, solids, viscosity, corrosion and conductivity each defeat a different kind of sensor. Floats get coated and stick, and foam can confuse an ultrasonic signal. A coated capacitive probe such as Gill LevelSlick has no moving parts and is designed for difficult conductive liquids.
Clean water is easy. Waste water, slurry, process chemicals, sludge and viscous fluids are not.
Floats get coated and stick. Contacts corrode. Foam and vapour sit on the surface where an ultrasonic signal expects liquid.
A level sensor that works for a month and then needs cleaning every week is not a solution. It is a maintenance task with a signal attached.
Difficult liquids need a sensor chosen for the liquid, not only for the tank.
No two difficult liquids alike
There is no single hard liquid, and no single answer. Foam, solids, viscosity, corrosion and conductivity each defeat a different kind of sensor, and some liquids combine several.
That is why the first question about a level application is always what the liquid is.
Coatings stop floats
Viscous and contaminated liquids coat moving parts until they stop moving. A capacitive probe has none.
No moving parts
Foam confuses the surface
Non-contact methods look for the surface. Foam and vapour can put a false surface above the liquid.
Conductive liquids need a specialist
Conductive liquids behave differently for capacitive sensing, which is why LevelSlick exists.
LevelSlick: challenging conductive liquids
Materials must match the medium
Wetted materials have to resist the liquid. Stainless steel suits many; aggressive media need coated sensors.
LevelPro: stainless steel
Four ways to read a hard liquid
Each approach suits some liquids and struggles with others. The table sets out the common patterns.
| Consideration | Float switch | Ultrasonic, non-contact | Hydrostatic pressure |  Capacitive, Gill LevelSlick and LevelPro |
|---|---|---|---|---|
| Contact with the liquid | Yes, moving float | No | Yes, sensor at the base | Yes, sealed probe with no moving parts |
| Foam and vapour | Usually unaffected | Can read foam as liquid | Unaffected | Depends on the liquid; discuss with our team |
| Coating and solids | Float can stick | Unaffected unless the sensor face is coated | Diaphragm can be fouled | LevelSlick designed for particles, suspended matter and viscous liquids |
| Output | Switched points | Continuous | Continuous | Continuous: voltage, current or resistive on LevelSlick |
| Best for | Simple high and low alarms in clean liquids | Open tanks where the surface is clean | Deep tanks and wells with stable density | Continuous level in liquids that defeat floats |
Non-contact ultrasonic sensing is often the best choice for a clean open surface. Capacitive sensing earns its place where the liquid coats, foams or carries solids.
Check the liquid first
Check the medium first
LevelSlick is for electrically conductive liquids. The liquid’s properties decide which sensor works, so the medium is always the first check.
Length is fixed by the probe
LevelSlick is available up to 2 m. Deeper tanks need a different approach.
Temperature has limits
LevelSlick operates from -40 to +85 degrees C. Hotter processes need another solution.
Some liquids need a custom build
Where no standard sensor suits the liquid, a custom capacitive sensor may, and that takes engineering time.
Probes built for bad liquids
All Gill level sensors are capacitive, with no moving parts, sealed solid-state electronics and factory calibration.
LevelSlick
Specialist sensor for challenging conductive liquids
An FEP coated probe, non-stick and low friction, for liquids with particles, suspended matter, viscosity or corrosive content, with tank profiling and full and empty alarms.
LevelPro
Robust stainless steel level sensor
Corrosion-resistant stainless steel for general liquids in industrial and process tanks.
Custom level sensors
Built for the liquid you have
Where the liquid, tank or interface rules out a standard sensor, a custom capacitive sensor can be developed.
insight
Conductivity changes the answer
Capacitive level sensing works by measuring how the liquid around a probe changes its capacitance. That change depends on the liquid’s electrical properties.
Oils and fuels are insulating and behave predictably. Water-based and conductive liquids, such as waste water or many process fluids, behave differently, and a standard probe can read them poorly.
LevelSlick is designed for challenging conductive liquids. Its coated probe separates the liquid from the sensing element, and its low friction surface resists the build-up that defeats floats.
That is why our team will always ask what the liquid is before anything else. The answer decides which sensor works, and whether a standard one will do.
The full explanation is in How does capacitive level sensing work?
Liquids that defeat floats
ApplicationSpecialist level sensing in cement and mining
Level in liquids as hard on sensors as the site.
ApplicationProcess fluid level monitoring
Continuous level in industrial process tanks.
ApplicationWater pumping station level monitoring
Level measurement in water and waste water.
IndustryIndustrial process
The wider process sensing picture.
Speak to our team
Tell us what you need to measure, where and under what conditions. We’ll help you work out the appropriate approach.
Difficult liquid questions
Waste water carries solids, grease and foam that coat floats and confuse some non-contact sensors. A capacitive sensor designed for conductive, contaminated liquids, such as Gill LevelSlick, gives continuous level with no moving parts. The exact choice depends on the liquid and the tank.
Float level sensors stick when viscous, contaminated or crystallising liquids coat the float and its guide, or when solids jam the mechanism. Removing the moving part, as capacitive sensing does, removes that failure mode.
An ultrasonic level sensor measures the time for a sound pulse to return from the surface, and foam or vapour can return an echo above the true liquid level. Where foam is common, a contact method such as a capacitive probe may give a more reliable reading.
A capacitive level sensor for conductive liquids uses a coated or insulated probe so that the liquid’s conductivity does not short the measurement. Gill LevelSlick is designed for challenging conductive liquids, including those with particles, suspended matter, viscosity or corrosive content.
Gill LevelSlick is available in lengths up to 2 m, with a BSP 1.25 inch thread, tank profiling and full and empty alarms. Deeper tanks need a different approach.
Yes. Where the liquid, tank or interface rules out a standard sensor, Gill can develop a custom capacitive level sensor. The starting information is the liquid, a tank drawing, the output required and the environment.