Browse Level Instruments
Continuous level measurement
Continuous level instruments measure the level across the full height of a vessel and send a live signal, typically 4–20 mA or a digital protocol, for remote indication, control and data logging. These instruments are usually called level transmitters.
Hydrostatic (pressure) level measurement
Suitable for: Liquids
Hydrostatic level measurement uses the pressure created by the weight of liquid above the sensor. A pressure transmitter is fitted at the bottom of the tank, or lowered in on a cable when top access is easier. The pressure is proportional to the liquid height, provided the liquid’s density is known and stable.
Submersible transmitters have a vent tube in the cable, so they measure against atmospheric pressure. In pressurised vessels, a differential pressure transmitter compares the pressure at the bottom with the pressure in the space above the liquid. Where only a local reading is needed, a simple pressure gauge can do the job.
Radar level transmitters
Suitable for: Liquids · Solids
Radar level transmitters give accurate, non-contact measurement for many liquids and solids. A microwave signal is sent from an antenna, reflects off the product surface and returns to the instrument. The time it takes to return tells the transmitter the distance to the surface, which it converts to level.
Because microwaves aren’t much affected by vapour, pressure or temperature changes above the product, radar suits a wide range of process conditions.
Guided wave radar
Suitable for: Liquids · Solids (granular)
Guided wave radar (GWR) sends a microwave pulse down a rod or cable probe that reaches into the product, rather than through the air from an antenna. The pulse reflects where it meets the product surface, and the instrument times the reflection, a technique called time domain reflectometry (TDR). Because the signal is guided, GWR performs well with foam, vapour, dust and turbulent surfaces, and can also detect the interface between two liquids.
Ultrasonic level transmitters
Suitable for: Liquids · Solids
Ultrasonic level transmitters measure level with sound. The sensor sends an ultrasonic pulse down to the product surface and times the echo, which is proportional to the distance from the sensor. They’re an economical, non-contact choice for liquids and solids in open or atmospheric-pressure vessels, such as water tanks, sumps and open channels. Heavy foam, dust, vapour or pressure can weaken the echo, so they aren’t suited to pressurised vessels.
Magnetic float level transmitters
Suitable for: Liquids
A buoyant float containing a magnet moves up and down a guide tube with the liquid level. Sensors inside the tube, either a chain of reed switches or a magnetostrictive sensor, detect the float’s position and convert it to a continuous level signal or a set of switch points. Magnetostrictive sensors give a particularly precise reading.
Capacitive level sensors
Suitable for: Liquids · Solids
Capacitive sensors measure the change in capacitance between a probe and the vessel wall as the product level rises and falls. They can give a continuous signal or act as a point level switch. Because the reading depends on the product’s dielectric properties, the sensor is set up for the material being measured, and build-up on the probe needs to be considered.
Point level detection
Point level instruments, or level switches, detect when the product reaches a set height. They switch a relay or electronic output to raise an alarm, start or stop a pump, or protect against overfilling or running dry.
Vibrating fork level switches
Suitable for: Liquids · Solids
A vibrating fork switch has a tuning fork driven by piezoceramic elements to vibrate at its natural frequency. When product covers the fork, the vibration is damped, and the switch changes its output. With no moving parts to wear, vibrating forks are a reliable, low-maintenance choice for high and low level alarms in both liquids and solids.
Conductivity level switches
Suitable for: Liquids (conductive only)
Conductivity switches detect conductive liquids, such as water and many process liquids. When the liquid reaches the probes, it completes an electrical circuit between them, or between a probe and the vessel wall, and the switch operates. Multiple probes of different lengths can control a pump between high and low levels.
Rotary paddle level switches
Suitable for: Solids
Rotary paddle switches detect the level of bulk solids in silos, bins and hoppers. A small motor slowly turns a paddle. When material covers the paddle and stops it turning, the switch detects this and changes its output.
Capacitive sensors and magnetic float switches can also be used for point level detection; see the continuous level section above.
Level gauges
Level gauges give a direct, local reading at the vessel. Because they work independently of your control system, they’re a valuable backup for operators and an important part of engineering risk management.
Types of level gauge
Suitable for: Liquids
Visual level gauges are typically based on pressure, a sight glass, a float, or a magnetic float.
A magnetic level indicator is a safer alternative to a sight glass. It mounts outside the vessel on a separate chamber, with a float that moves with the liquid level. A column of magnetic flags on the outside flips colour to follow the float, giving a clear reading without glass in contact with the process.
Connections and accessories
We supply a wide range of process connections, switches and isolation valves for level gauges, and can help with custom scales.
Choosing the right level instrument
The first decision is what you need the instrument to do.
• Level transmitters give a continuous signal for remote indication, control and data logging, as an analogue signal such as 4–20 mA or 0–5 V, or over a digital communication protocol.
• Level switches detect a single set point, opening or closing a contact for an alarm or control action.
• Level gauges give a local visual reading that works independently of your control system.
We then consider the details of your application:
• the product’s properties, including whether it’s a liquid, slurry or bulk solid
• the process connection and vessel details
• the pressure and temperature of the product and its surroundings
• your preferred units of measurement and output type
• power, installation and maintenance requirements
• hazardous area, compliance and certification requirements.
Which technology suits your product?
| Technology | Liquids | Solids | Measurement |
|---|---|---|---|
| Hydrostatic (pressure) | ✓ | – | Continuous |
| Radar | ✓ | ✓ | Continuous |
| Guided wave radar | ✓ | ✓ (granular) | Continuous |
| Ultrasonic | ✓ | ✓ | Continuous (atmospheric vessels) |
| Magnetic float | ✓ | – | Continuous or point |
| Capacitive | ✓ | ✓ | Continuous or point |
| Vibrating fork | ✓ | ✓ | Point |
| Conductivity | ✓ (conductive only) | – | Point |
| Rotary paddle | – | ✓ | Point |
| Level gauge | ✓ | – | Local display |
As well as supplying the right instrument, we can service and repair many types of instruments to keep your measurement running. See our Calibration & Service page for more.
Frequently asked questions (optional)
Should I use radar or ultrasonic level measurement?
Both are non-contact. Ultrasonic is an economical choice for open or atmospheric-pressure vessels with clear conditions. Radar handles vapour, pressure, temperature changes and difficult surfaces better, so it suits a wider range of process vessels.
How do I measure level in a pressurised tank?
Use a differential pressure transmitter, which compares the pressure at the bottom of the tank with the pressure above the liquid, or a radar or guided wave radar transmitter, which isn’t affected by the vessel pressure.
What’s the difference between a level transmitter and a level switch?
A level transmitter gives a continuous reading of the level across its range. A level switch only tells you whether the product has reached one set point, and is used for alarms, pump control and overfill protection.
Which level switch suits powders and bulk solids?
Vibrating fork switches designed for solids, and rotary paddle switches, are both widely used for silos, bins and hoppers. Capacitive switches are another option for some materials.
Is there a safer alternative to a sight glass?
Yes. A magnetic level indicator mounts on a chamber outside the vessel and uses flip flags driven by a magnetic float, so there’s no glass in contact with the process.