Measurement & Process Instrumentation
Continuous and point level instruments - radar, ultrasonic, hydrostatic, capacitance and float - for tanks, silos and interfaces.
Level is the measurement of a boundary rather than of a quantity: the surface between a liquid and the vapour above it, between two immiscible liquids, or between a solid and the air in a silo. Almost every difficulty in the category comes from the state of that boundary. Foam, vapour, condensation, agitation, build-up and a moving surface all change how the instrument sees it.
The practical split is between continuous measurement, which reports a value through the whole range, and point level, which reports only whether the product has reached a position. Many installations need both: a continuous transmitter for inventory and a point switch for a high-level interlock that does not depend on the transmitter being correct.
Instrument choice follows the medium and the tank rather than the accuracy requirement. A clean water tank in an open sump and a pressurised reactor with a condensing vapour are the same measurement in principle and entirely different problems in practice.
| Product type | How it works | Usually specified for |
|---|---|---|
| Radar level transmitter | Time of flight of a microwave pulse reflected from the surface | Tanks and silos with vapour, foam or a varying dielectric; non-contact models tolerate agitated and hygienic processes |
| Guided wave radar | The same principle along a probe, which concentrates the return echo | Low-dielectric media, narrow vessels and stilling wells where a free-space beam would be disturbed |
| Ultrasonic level transmitter | Time of flight of an acoustic pulse through the vapour space | Water, wastewater and simple liquid storage where the vapour space is clean and the temperature is stable |
| Hydrostatic level transmitter | The pressure exerted by the column of liquid above the sensor | Vented tanks of known density, and wells and sumps where a simple submersible device is preferred |
| Differential pressure level | Difference between the wet leg and the measured leg of a closed tank | Pressurised and closed vessels where the top pressure must be cancelled out |
| Capacitive level sensor | Change in capacitance between a probe and the vessel wall | Short-range and point duties on clean liquids and powders |
| Float and displacer | Buoyancy acting on a float or a displaced volume | Interface measurement and simple, very reliable high-level duties |
| Vibrating fork and tuning fork switch | A change in resonant frequency when the fork is covered | Point level on liquids and powders, including high and low alarms on sticky or foaming media |
| Rotary paddle and capacitance point switch | A paddle stalls, or capacitance changes, when the product reaches it | Bulk solids, bin high-level and plug detection where a mechanical answer is acceptable |
Level gauges, sight glasses and magnetic float indicators give a direct visual reading and are listed under this category alongside the transmitters.
There is rarely a single correct instrument for a duty, but there is always a shortlist that can be justified and a set of answers that eliminates the rest. These are the questions that decide it.
| Technology | Best suited to | Limits | Typical medium |
|---|---|---|---|
| Radar, non-contact | Vapour, foam, pressure and temperature; hygienic vessels | A very low dielectric constant can weaken the echo; condensation on the antenna distorts it | Chemicals, hydrocarbons, water, food products |
| Guided wave radar | Low-dielectric media and cramped vessels | The probe can be coated or bridged by build-up; not suited to heavy solids | Solvents, light oils, clean liquids |
| Ultrasonic | Simple liquids in open or vented tanks | Temperature stratification, vapour, foam and condensation all affect the speed of sound or the echo | Water, wastewater, non-hazardous storage |
| Hydrostatic | Clean liquids of known and stable density | Density changes shift the reading with no change in level; blocked impulse lines are a common failure | Water, fuels, dilute solutions |
| Differential pressure | Closed and pressurised vessels | Both legs must be rated for the vessel pressure; a wet leg must never run dry | Process vessels, boilers, columns |
| Point switches | Alarms, interlocks and pump protection | They report a position, not a value, and cannot be used for inventory | Liquids, slurries and bulk solids depending on the type |
What is left after the technology is chosen is a list of values that only the installation can supply. These are the ones that change the model, the price or the lead time:
Specifications vary by model and application, so no performance figure is stated on this page. Where a parameter has not been documented for a particular model, the product page says so rather than filling the gap with a plausible number. Send the values above and we will return the ones the selected model actually holds.
Frequently asked
The questions that come up before an order rather than after it. If yours is not here, send it with the requirement and we will answer it in the quotation.
Radar is the more tolerant of the two: it works through vapour, handles pressure and temperature extremes, and is unaffected by the speed of sound changing with temperature. Ultrasonic depends on that speed and struggles with stratification, foam and heavy condensation, but it is the economical answer for simple liquids in open or vented tanks. If the vapour space is anything other than clean air, radar is usually the better starting point.
For a hydrostatic instrument it is usually the density, which shifts with temperature while the level stays the same. For an ultrasonic instrument it is usually the speed of sound changing with temperature stratification, or condensation on the transducer. For radar it is often build-up on the antenna or a foam layer that moves the reflection point. Identifying which of the three you have decides the fix.
Where the high level is a safety or containment function, yes. An independent point switch exercises a different principle and a different failure mode from the transmitter, so a common cause failure is much less likely. It is also standard practice for the interlock to be independent of the instrument used for control and inventory.
Some can. Guided wave radar and displacer instruments handle a distinct interface where the two liquids have different dielectrics or densities, and the instrument is configured for the interface rather than the total level. Where the emulsion layer is thick or unstable, the problem is usually the process rather than the instrument, and that is worth stating at the enquiry stage.
The tank dimensions and type, the medium and its behaviour, the vapour-space conditions, the process connection and the measurement path. Also tell us whether the duty is continuous or point, whether an independent switch is wanted, and the accuracy genuinely required. Tank geometry details save a round of questions more reliably than anything else.
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RLM-80 · Radar Level Meters Reference listing
Non-contact radar level transmitter for liquids and bulk solids, measuring through vapour, dust and foam without touching the medium.
Send the specification and we will confirm the matching instrument, availability and lead time. Minimum order quantity is 1 pc.
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Send the technical detail and we will confirm availability, lead time and terms. In-stock items ship within 48 hours; customized specifications typically take 2-10 days. Minimum order quantity is 1 pc.