Product type
A radar level meter sends microwaves towards the surface of a liquid or a solid and times the return. Because the time of flight is converted into a distance and the tank geometry into a level, the instrument measures without touching the contents. That is what makes it the practical answer in tanks holding corrosive, hygienic, viscous or hot material, and in silos where dust would defeat an optical or mechanical device.
A radar level meter sends microwaves towards the surface of a liquid or a solid and times the return. Because the time of flight is converted into a distance and the tank geometry into a level, the instrument measures without touching the contents. That is what makes it the practical answer in tanks holding corrosive, hygienic, viscous or hot material, and in silos where dust would defeat an optical or mechanical device.
Radar is not disturbed by the things that trouble sound waves. Steam, vapour, temperature stratification and, to a large extent, atmospheric pressure do not change the speed of the measurement in the way they change the speed of sound, which is why radar has displaced ultrasonic instruments in many steam and condensate duties. What does affect it is how much of the microwave energy comes back, and that depends mainly on the dielectric constant of the material and the condition of its surface.
Two families are in common use. Free-space radar radiates from an antenna mounted in the tank roof and touches nothing. Guided wave radar sends the signal down a probe that reaches into the product, which suits low-dielectric media, narrow tanks and agitated surfaces, at the cost of a wetted probe that the process can foul or coat.
The instrument measures time of flight. A short pulse or a frequency sweep is transmitted, reflected from the surface and received, and the elapsed time gives the distance. The level follows from that distance and the known position of the reference plane, which is why the tank height and the nozzle dimensions are part of the specification rather than site detail.
How strong the echo is depends on the contrast in dielectric constant between the material and the space above it. A material with a high dielectric constant reflects strongly and is easy to see. A low-dielectric material returns little energy, so the choice moves towards a guided wave probe or a more focused antenna, and towards ensuring that as much transmitted energy as possible reaches the surface.
The other half of the problem is everything else in the tank. An agitator blade, a heating coil, a baffle, a filling stream and condensation on the antenna all produce reflections of their own, and a receiver cannot tell a false echo from a real one by strength alone. Echo curve analysis and mapping are what suppress them, and they work best when the installer knows what is in the vessel. That is why the internal fittings belong in the enquiry.
Most of the specification is fixed by these decisions rather than by the accuracy class. Each one constrains the next, which is why they are settled in order.
| Configuration | Options to fix | What it actually decides |
|---|---|---|
| Measurement principle | Free-space radar or guided wave radar | Whether the instrument touches the medium, and how well it copes with weak reflections, foam and surface movement. |
| Antenna or probe form | Horn, lens, rod and cable forms, in different sizes | The beam angle, and therefore how much of the tank’s internal structure falls inside the beam and can create a false echo. |
| Frequency band | The radar bands offered by the instrument family | How tightly the beam can be focused from a given antenna size, which matters on tall or obstructed vessels. |
| Output and protocol | 4-20 mA, HART, Modbus and other buses | What reads the level, and whether the instrument can be configured and diagnosed remotely. |
| Power and wiring | Two-wire loop powered or four-wire with a separate supply | Whether the existing loop can power the instrument, and how much cabling the installation needs. |
| Process connection and materials | Thread, flange or hygienic fitting, and the wetted materials | Mechanical fit, sealing method, and compatibility with the medium and with cleaning. |
| Enclosure and area rating | Housing material, ingress protection, hazardous-area approval, hygienic design | Where the instrument may be installed and whether it can be washed or cleaned in place. |
| Configuration and display | Integral display, remote configuration, or software and wireless access | Commissioning effort, and whether anybody needs to read a value at the vessel. |
| Factor | Why it decides the answer | How to settle it before enquiring |
|---|---|---|
| Dielectric constant of the material | It sets how much energy comes back, and therefore whether a free-space antenna can see the surface at all | Give the product name and, where it is known, its dielectric constant. Do not assume a material reflects well because it looks solid. |
| Measuring span, blanking distance and the lowest level | The top and bottom of the usable range are set by the antenna and the connection, not by the tank height alone | Give the tank height and the minimum and maximum level that actually have to be measured, not just the vessel dimensions. |
| Tank geometry and internal fittings | Agitators, coils, baffles and filling points all reflect, and the receiver has to be told what to ignore | Send a sketch of the vessel and its internals, and say where the filling line enters. |
| Surface condition | Foam, waves, condensation and build-up change both the echo and the antenna’s ability to transmit | Describe what the surface does in service, including during filling and any foaming duty. |
| Atmosphere above the product | Vapour, dust, and the pressure and temperature in the space above the liquid or solid affect the antenna and the sealing | State the vapour or dust present, and the pressure and temperature in the vapour space. |
| Process connection and materials | It fixes the mechanical fit and the compatibility, and often the antenna size that will physically pass the nozzle | Give the nozzle size and standard, and the material of construction of the tank. |
| Output, loop power and integration | The existing loop and the receiving system decide the output and the wiring arrangement | Name what reads the level and whether the loop can power the instrument. |
| Cleanability and area classification | These change the housing and the fitting, and in hygienic duty also the antenna surface | State clean-in-place requirements and the area classification. |
These are the types an enquiry for a radar level meter usually turns out to be, and the point at which the choice is genuinely decided.
| Nearest alternative | What separates it from radar |
|---|---|
| Ultrasonic level meters | Uses sound rather than microwaves, and usually costs less. The speed of sound changes with temperature, vapour composition and pressure, so steam, stratification and vacuum degrade the reading in ways that do not affect radar. Where none of those are present, ultrasonic is often the more economical choice. |
| Guided wave radar transmitters | The same radar principle applied along a probe rather than through the air, which steadies the reading on low-dielectric products, in narrow vessels and on agitated surfaces. It requires a wetted probe, so coating and fouling become new considerations. |
| Capacitive level sensors | Measures the change in capacitance as the product rises between probe and wall. Simple and inexpensive, and workable at low dielectric constants, but the reading depends on the product’s properties, so a change of medium or of moisture content usually means recalibration. |
| Hydrostatic level transmitters | Infers level from the pressure of the liquid column. Simple, well understood and inexpensive, but the answer is really a pressure, so a change in density changes the indicated level, and the arrangement suits open tanks rather than pressurised vessels. |
| Float level sensors | A mechanical float that follows the surface, requiring no power and giving a direct indication. Dependable in clean liquids, but moving parts wear and stick, and viscous, coating or solids-bearing products defeat them. |
| Level switches | Reports that a point has been reached rather than measuring where the level is. Interlocks and high-level alarms normally want a switch, often alongside a continuous instrument rather than instead of one. |
Radar and ultrasonic are the two non-contacting families, and the difference between them is almost entirely about what is in the space above the product.
The first reply can be a quotation rather than a set of questions if the enquiry carries these. Where a figure is not known, send the duty description and we will confirm what it implies.
Available products
MIK-RD908 (3 models) · Radar Level Meters
Radar level meter in 80 GHz, low-frequency and guided-wave series for tanks, silos, rivers and pressurised vessels, with spans from 10 m to 80 m.
Also in Level Measurement
Every type we quote for under Level Measurement. A type with no link yet is still quoted for - it is described on the Level Measurement overview, and gets a page of its own as soon as a model is published against it.
Frequently asked
Look at the space above the product rather than at the product. If there is steam, heavy vapour, temperature stratification, vacuum or a dusty atmosphere, radar is the more dependable choice because those conditions change how fast sound travels but not how fast microwaves do. In a clean, vented, room-temperature tank with no condensation, ultrasonic normally does the job for less.
When the reflection is weak or the surface is uncooperative. A probe carries the energy to the product and back along a defined path, so it holds up on low-dielectric media, in narrow vessels, on foaming or agitated surfaces and where the nozzle geometry would leave a free-space antenna with too little room. The trade is a wetted probe that can coat, foul or corrode, so the medium has to be considered as well.
Not by itself. It reduces how much energy is reflected, which makes the measurement harder rather than impossible. What it changes is the configuration: a guided wave probe, a larger or more focused antenna, or a different mounting position. The figure is still worth supplying, because it is the single number that most affects whether the instrument will find the surface.
Because a radar receiver sees every reflection, not only the one from the surface. An agitator blade, a heating coil or a filling stream returns energy that looks like a level until the instrument has been taught to ignore it. That teaching is done from a description or a sketch of the vessel internals, so the more accurately they are described, the more reliable the reading from the first day.
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