Level Measurement
Level Measurement – reliable level, volume & limit detection for tanks and vessels
Level sensors and point level switches provide continuous level/volume or min/max alarms in liquids, pastes, foams and bulk solids. Depending on medium and process conditions, technologies include hydrostatic, radar/FMCW, ultrasonic, capacitive, conductive, magnetostrictive, guided wave radar (TDR), float-based and optical methods.
Features (model-dependent): high-temperature/high-pressure, hygienic design (EHEDG, FDA), ATEX/IECEx, SIL, foam/steam immunity, multi-point measurement, built-in volume calculation and communications (4–20 mA/HART, Modbus/RS-485, Profibus/Profinet, EtherNet/IP, IO-Link).
ICS Schneider Messtechnik supports principle selection, sizing (geometry, dead/blank zones), materials, calibration, documentation and integration into PLC/SCADA/IIoT.
FAQ on Level Measurement
Answers on measuring principles, selection criteria, installation, accuracy, media, hygiene/ATEX, calibration and troubleshooting.
Which measuring principle fits my medium?
| Principle | Media | Strengths | Notes |
|---|---|---|---|
| Hydrostatic (pressure) | Liquids | Compact, cost-effective | Compensate density/temperature |
| Radar/FMCW | Liquids/bulk solids | Foam/steam tolerant, precise | Clear view, antenna selection matters |
| Guided wave radar (TDR) | Liquids, interfaces | Insensitive to internals | Probe length must match range |
| Ultrasonic | Liquids/bulk solids | Non-contact, economical | Watch for steam/turbulence |
| Capacitive | Liquids/pastes | Simple point level | Product build-up needs tuning |
| Conductive | Water/conductive media | Very robust, low-cost | Requires minimum conductivity |
| Magnetostrictive | Liquids | High accuracy, multi-float/interface | Needs float(s) |
| Float/switch | Liquids | Simple, no parameterization | Mind mechanics/space |
| Optical (fork/light) | Clear media | Compact, fast | Sensitivity to fouling |
Continuous measurement vs. point level—what’s the difference?
Continuous sensors output an analog/digital profile (e.g., 4–20 mA) of level/volume. Point level switches give on/off at min/max for overfill and dry-run protection.
How do foam, steam and condensation affect results?
Radar/TDR handle foam/steam better than ultrasonic. With heavy condensation add purge/heating and choose suitable antennas (PTFE/PP domes, horn). Ultrasonic needs a free, dry sound path.
When is TDR better than free-space radar?
In narrow tanks, with internals/agitators or at low dielectric constants. TDR also excels at interface (oil/water) measurement.
How do I choose antenna/probe types?
By temperature/pressure, medium and space: horn, rod, cable probes (TDR), hygienic flush domes, corrosion-resistant linings (PTFE/PFA) and seals (EPDM/FKM/PTFE).
What accuracy is realistic?
Radar/TDR typically ±2…10 mm; hydrostatic ±0.1…0.25% FS; ultrasonic ±0.25…0.5% FS (application-dependent). Installation and setup drive practical accuracy.
How do I handle dead zones/blanking distances?
Mount so the zero reference sits above the blanking zone. For radar, observe near range (e.g., 50–150 mm); size TDR probes to reach near the bottom with a safety offset.
Can the device output volume directly?
Yes—many transmitters offer tank strapping tables/linearization (e.g., horizontal cylinder) to calculate volume/remaining content with temperature compensation.
What matters in hygienic applications?
316L, dead-space-free clamp/Varivent, EHEDG/FDA seals, polished surfaces and CIP/SIP resistance. Provide material and compliance certificates.
How do density and temperature changes influence readings?
For hydrostatic sensors results scale with density—use compensation or fixed density. Radar/TDR are largely density-independent.
Where is the ideal mounting location?
Away from inlets, agitators and walls. On sloped/conical roofs aim radar toward the surface. Mount stress-free; in bulk solids consider the fill cone.
How long should a TDR probe be?
Probe length ≈ measuring range + safety margin (respect upper/lower blocking distances). For interfaces configure both phases or use dual floats.
What’s special about bulk solids?
80 GHz radar with narrow beam is ideal for deep silos; compensate dust, use air purge/membrane windows. Robust point switches: vibrating forks or rotary paddles.
Which outputs/communications are available?
4–20 mA/HART, relay/PNP/NPN, pulse, Modbus/RS-485, Profibus/Profinet, EtherNet/IP, IO-Link. Diagnostics: foam detection, signal quality, echo curves.
How are parameterization & calibration done?
Via keys/display, DTM/EDD/software or IO-Link. Set zero/span, load strapping tables, inspect echo profiles. Hydrostatic: set zero at empty/defined level.
What ATEX/SIL options exist?
Many sensors are available in Ex i / Ex d for Zone 0/1/2 and dust zones, with SIL2/3 ratings. In hazardous areas use proper barriers/isolators and device categories.
Typical pitfalls & quick fixes
- False echoes from internals → re-aim sensor and set ignore zones
- Foam/steam disturbing ultrasonic → choose radar/TDR
- Hydrostatic drift → density/T compensation, vent lines, check capillaries
- Wrong probe length → match to measuring range
- Fouling buildup → add purge, choose suitable coatings/materials
How do I select the right process connection?
By DN/space, cleanability and pressure: G/NPT, clamp/Varivent, flanges (PN/ANSI), hygienic flush. Provide strain relief for long TDR probes.
How do I convert level to mass/inventory?
Level → volume using geometry/strapping; volume × density(T) → mass. Many transmitters compute and output t/kg directly.
Maintenance & lifecycle—what’s sensible?
Sensors are low-maintenance. Periodically check tightness, fouling, cabling/EMC; set calibration intervals per QA/standards and backup parameters.
Do you support selection, sizing & commissioning?
Yes. We analyze your medium/process, choose the best principle, define mounting/aim, provide calibration certificates and integrate the measuring point into PLC/SCADA/cloud with full documentation.