Level transmitter

01

Match the technology to the liquid

Endress+Hauser's comparison of continuous level technologies lists, for each, what limits it: non-contact and guided radar cannot measure liquids with a dielectric constant (DC) below 1.4; capacitance needs DC above 2.0 and is affected by conductivity changes; hydrostatic measurement is affected by changing density and by dynamic pressure from agitators or vortices. [1]

The same sheet gives accuracy (typ.) of ±2 mm for 26 GHz and ±1 mm for 80 GHz non-contact radar, ±2 mm for guided radar under 15 m and ±10 mm beyond, ±1% of range for capacitance and ±0.05% of set span for hydrostatic. These are best-case instrument figures; installation and process conditions decide what you actually get. [1]

Editorial calculation (ρgh): a hydrostatic transmitter reads pressure, so the same 1 m of liquid gives about 9.8 kPa for water and about 11.8 kPa for a liquid of density 1,200 kg/m³. If density changes and the transmitter is not compensated, the level reading changes with it.

Give the supplier the liquid, its dielectric constant if known, density and how much it varies, conductivity, temperature and pressure. These decide the technology before range and output do.

02

Check foam, vapour, build-up and agitators

Endress+Hauser lists foam, extreme turbulence and build-up on the antenna as affecting non-contact radar, with wall effects and interfering reflections affecting accuracy; guided radar is affected by extreme build-up and limited by strong mechanical stress from agitators. [1]

In Control Global, Béla Lipták explains that guided wave radar sends pulses down a probe and times the reflection; a rising dielectric constant in a hot vapour space slows the pulse so the level reads low, which a reference target on the probe can correct. Thick, high-dielectric coating along the probe is the worst error source, and readings may be non-linear within about 18 in of the probe ends. [2]

He adds that agitators, thick foam, condensation or splashing cause problems for non-contact pulse radar. [2]

03

Check temperature, pressure and range limits

Endress+Hauser gives guided radar a process range of −196 to +450 °C and −1 to +400 bar, capacitance −80 to +200 °C and −1 to +100 bar, and hydrostatic −70 to +400 °C from vacuum to +420 bar, with hydrostatic unsuitable for vacuum combined with temperatures above +200 °C. [1]

These are limits across a manufacturer's whole range. A given model, seal or antenna will have narrower limits; ask for the limits of the exact model and process connection you are buying.

04

Radar, submersible and buoyancy types on supplier sites

BCST lists non-contact, guided wave and coaxial guided wave radar; Shengke lists 80 GHz radar and non-invasive ultrasonic level sensors; Sentec lists hydrostatic, ultrasonic, radar, magnetostrictive and capacitive transmitters; Lefoo and Rika list submersible level transmitters; HollySys lists buoyancy level transmitters and magnetic level gauges. Ask each for the model's dielectric, temperature and pressure limits. [3] [4] [5]

05

From antenna or diaphragm to the output electronics

Only the sensing element changes with the technology: an antenna, a probe, a diaphragm or a float. The connection, seal and housing rows are where tank and site details go.

06

Range, accuracy, output and wetted-material entries

Accuracy, process temperature and pressure all depend on the technology chosen above, so settle that first and then fill these rows for the exact model.

07

Send the liquid, vessel and signal data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Liquid: [name; dielectric constant; density and variation; conductivity; viscosity; coating tendency]
Process: [temperature; pressure or vacuum; foam; vapour or condensation; agitator]
Vessel: [height; material (metal or plastic); nozzle size and height; internals; stilling well]
Measurement: [range; accuracy; level or interface]
Signal: [4–20 mA, HART or other; supply; display]
Approvals: [hazardous area; SIL if required; IP rating]
Documents: [datasheet; dielectric and temperature limits; calibration certificate]

See manufacturer records Send an enquiry through CNFX