Coltraco Ultrasonics provides non-invasive measurement technologies for engineers, operators and maintenance teams who need to verify tank liquid level without unnecessary disruption. This page explains ultrasonic tank level measurement, how conventional top-mounted ultrasonic sensors differ from Coltraco’s Portatank®, and how ultrasonic methods compare with dipsticks, sight glasses, float gauges and hydrostatic pressure measurement.
Ultrasonic tank level measurement uses high-frequency sound waves to identify liquid level or liquid presence. In conventional top-mounted systems, an ultrasonic level sensor sends sound waves through the air space towards the liquid surface. Coltraco’s Portatank® works differently: it is a handheld external ultrasonic liquid level indicator used against the tank wall to detect the presence or absence of liquid behind the measurement point.
What Is Ultrasonic Tank Level Measurement?
Ultrasonic tank level measurement is a way of using sound energy to determine where liquid sits inside a tank, vessel or storage system. The exact method depends on the sensor design.
A conventional ultrasonic tank level sensor is usually mounted above the liquid. It emits sound waves through the air space, receives the echo from the liquid surface and calculates the distance to that surface using time-of-flight principles. This type of tank level sensor is often used where continuous level measurement is required.
An external portable ultrasonic tank level indicator such as Portatank® is used differently. The operator places the sensor on the outside wall of a suitable tank. The device helps identify whether liquid is present behind that measurement point, allowing the user to build a picture of tank liquid level without installing a permanent top-mounted sensor.
How Does Ultrasonic Tank Level Measurement Work?
Conventional top-mounted ultrasonic level sensors work by sending a sound pulse down through the vapour space above the liquid. The pulse reflects from the liquid surface, returns to the sensor and is converted into a distance measurement. The system can then calculate tank level from the known tank geometry.
This method can work well, but it is influenced by air-space conditions. Temperature, vapour, foam, turbulence, surface agitation and gas composition can all affect the sound path or the quality of the surface reflection. These factors mainly apply to conventional top-mounted time-of-flight ultrasonic sensors because their measurement depends on a clear acoustic path through the headspace and a readable reflection from the liquid surface.
Portatank® does not operate as a permanent top-mounted continuous level sensor. It is a portable external liquid level indicator. The sensor is coupled to the outside of the tank wall, where it sends ultrasound through the wall and helps the user distinguish between liquid and non-liquid conditions behind the measurement point.
Traditional Tank Liquid Level Methods
Traditional gauges and direct methods still have a place. A simple low-risk tank may not need a portable ultrasonic instrument or a fixed tank level sensor. The limitation is that many older methods depend on manual access, moving parts, visual judgement or assumptions about the liquid.
Dipsticks and Manual Tape Systems
Dipsticks and tapes are simple, inexpensive and familiar. They can work well where the tank is easy to access, the liquid is safe to expose, and a periodic manual reading is enough.
Their weakness is that they usually require opening or accessing the tank contents. This can introduce contamination risk, create exposure concerns or make the reading unsuitable for tanks that should remain closed during operation.
Sight Glasses
A sight glass provides a direct visual indication of tank liquid level. It is useful when it is clean, readable and installed in a location where the operator can see it safely.
Over time, sight glasses can become cloudy, stained or difficult to interpret. Human reading error also remains possible, particularly where lighting, access or scale markings are poor.
Float Gauges
A float gauge uses a buoyant element that rises and falls with the liquid level. It can be simple and effective, especially in tanks where internal installation is acceptable.
Float mechanisms can stick, foul or become misaligned. If the float no longer moves freely, the gauge may show a level that does not match the actual liquid inside the tank.
Capacitance Measurement
Capacitance gauges depend on changes in electrical properties between the probe, tank and liquid. They can be useful in suitable applications, but performance depends on the liquid’s dielectric properties and the condition of the probe.
Build-up, coating, conductive fluids or changes in product characteristics can affect the reading. For some tanks, this makes calibration and maintenance especially important.
Hydrostatic Pressure Measurement
Hydrostatic pressure measurement estimates level from the pressure exerted by the liquid column. It can be accurate where liquid density is stable and pressure tapping or sensor installation is acceptable.
The main limitation is that the reading depends on density, pressure reference and temperature. If density changes, the calculated level may change even when the physical liquid level has not.
How Does Ultrasonic Measurement Compare With Traditional Tank Level Methods?
The right liquid level measurement method depends on the tank, liquid, risk level and inspection objective. Ultrasonic measurement is not automatically better than every traditional method. It is often most useful where a team needs reliable information without unnecessary tank access or permanent modification.
| Method | How It Works | Main Advantage | Potential Limitation |
| Dipstick | A marked stick or tape is inserted into the tank to show liquid height. | Simple, low cost and suitable for many low-risk manual checks. | Usually requires access to the tank contents and may introduce contamination or exposure risk. |
| Sight glass | A transparent tube or window shows the liquid level visually. | Direct visual indication without complex electronics. | Can become cloudy, stained or hard to read, and still relies on human judgement. |
| Float gauge | A float rises or falls with the liquid and drives a local indicator. | Straightforward indication where internal installation is acceptable. | Moving parts can stick, foul or give a misleading reading. |
| Hydrostatic pressure measurement | A pressure sensor estimates level from the pressure of the liquid column. | Useful for continuous measurement where density is stable. | Accuracy can be affected by density, temperature and pressure reference changes. |
| Conventional top-mounted ultrasonic sensor | A fixed sensor sends sound waves through the air space and measures the echo from the liquid surface. | Supports continuous non-contact level measurement in suitable tanks. | Foam, vapour, turbulence, temperature and surface reflection can affect performance. |
| External portable ultrasonic measurement, such as Portatank® | A handheld sensor is placed against the tank wall to detect liquid presence or absence behind the measurement point. | Useful for periodic external checks on existing suitable tanks without top-mounted installation. | Requires suitable tank wall contact, correct technique and an application where external ultrasonic measurement is appropriate. |
What Are the Advantages of Ultrasonic Tank Level Measurement?
Ultrasonic tank level measurement can reduce the need for manual access and help engineers obtain more consistent readings than purely visual methods. In conventional fixed installations, an ultrasonic level sensor can support continuous monitoring without touching the liquid. In portable external inspection, an ultrasonic tank level indicator can help technicians check an existing tank without adding a permanent sensor.
The main advantage is operational practicality. A fixed ultrasonic system may suit a process tank that needs ongoing level data. A portable instrument may suit an inspection team that needs to check multiple storage tanks, transformer tanks or industrial vessels as part of periodic maintenance.
Accuracy still depends on the application. With conventional top-mounted ultrasonic sensors, air-space conditions and surface reflection matter. With Portatank®, sensor coupling, tank material, wall condition, internal structures, liquid type and operator technique all affect the result. The method must match the measurement problem.
Where Is Ultrasonic Tank Level Measurement Used?
Ultrasonic tank level measurement is used across industrial tanks and storage tanks where operators need better visibility of tank liquid level. Relevant applications include manufacturing, oil and fuel storage, chemical processing, utilities, power generation, water treatment, wastewater management, marine systems and fluid handling.
In manufacturing, liquid level measurement supports stock control and helps avoid production delays caused by unexpected shortages. In fuel and oil storage, accurate level information supports logistics and maintenance planning. In chemical processing, tank level information can help reduce the risk of overflow or unsafe handling. In water and wastewater management, level information may support treatment, pumping and capacity decisions.
External portable ultrasonic measurement is particularly useful when the tank already exists and permanent modification would be undesirable. It can also help where a built-in gauge needs checking because the reading is unclear or suspected to be wrong.
Coltraco Portatank® Ultrasonic Tank Level Indicator
Coltraco’s Portatank® is a handheld, portable ultrasonic tank level indicator for liquid level measurement in suitable tanks. It is used externally against the tank wall and helps detect the presence or absence of liquid behind the point being tested.
This is the key distinction: Portatank® is not a permanently installed continuous level sensor and it is not a conventional top-mounted ultrasonic level sensor. It does not depend on sending sound waves through the air space above the liquid surface. It is designed for periodic inspection from outside the tank wall.
Portatank® can be used across multiple suitable tanks rather than being dedicated to one fixed installation. Current Coltraco product information describes it as suitable for tanks of various materials, with a tank working range of approximately 0.5 metres to 15 metres plus, and an accuracy of approximately ±10mm. It is intended for single-skinned tanks and works on most metals, plastics and glass where the application and wall contact are suitable.
The instrument includes a visual LED indication and oscilloscope functionality to support interpretation and troubleshooting. Coltraco’s wider liquid level indicator range includes products for tanks, pipes, cylinders and fixed monitoring, so users can compare the most appropriate option for the asset being inspected.
How Can You Improve Tank Level Measurement Accuracy?
Accurate tank level measurement starts with choosing the right method. For conventional top-mounted ultrasonic sensors, the installation must account for air-space conditions, surface reflection, temperature, vapour, foam, turbulence and the distance to the liquid surface.
For Portatank®, the user should focus on external measurement conditions. The tank should be suitable for external ultrasonic testing, and the sensor must make good contact with the wall. Single-skinned tanks, appropriate wall materials and a clear measurement path are important.
Good practice also includes checking more than one point where needed, avoiding welds or poor surface contact where possible, and interpreting readings in context. Internal structures can affect ultrasonic response, so difficult tank geometries may require additional care.
Ultrasonic tank level measurement is an engineering measurement, not just a device reading. The tank, liquid, sensor position and operator technique all matter.
Coltraco’s Portatank® usage guidance provides further information on practical liquid level testing and sensor positioning.
Learn More About Portatank®
The Portatank® ultrasonic tank level indicator from Coltraco is designed for external, portable liquid level inspection where the tank and application are suitable. It offers a practical periodic checking method for many industrial tanks, especially where a sight glass, float gauge or manual access method is difficult to rely on.
Learn more about the Portatank®
Speak to Coltraco
Coltraco is a British manufacturer of ultrasonic technologies, exporting to 120 countries and twice winner of The Queen’s Award in 2019 and 2022.
FAQs
How do you measure liquid level in a tank using ultrasonic technology?
Two ultrasonic approaches relevant to this comparison are conventional top-mounted measurement and external portable measurement. A conventional top-mounted ultrasonic level sensor sends sound waves through the air space towards the liquid surface and uses the returning echo to calculate level. Coltraco’s Portatank® works differently: it is placed externally against the tank wall to help detect whether liquid is present behind the measurement point.
Can Coltraco Portatank® measure liquid level without drilling into the tank?
Yes, where the tank and application are suitable. Portatank® is a handheld external ultrasonic liquid level indicator used against the tank wall. It does not require permanent top-mounted installation, drilling or cutting, and it can be used across multiple suitable single-skinned tanks.
Is an ultrasonic tank level indicator always more suitable than a sight glass or dipstick?
No. A dipstick, sight glass or float gauge may be enough for a simple, low-risk tank that can be accessed safely. Ultrasonic measurement is often more useful where the tank should remain closed, where a built-in gauge is unclear or unreliable, or where technicians need an external periodic inspection method.
What affects the accuracy of ultrasonic tank level measurement?
For conventional top-mounted ultrasonic sensors, accuracy can be affected by temperature, vapour, foam, turbulence, gas composition and the quality of the surface reflection. For Portatank®, accuracy depends more on tank suitability, single-skinned wall contact, coupling, wall material, surface condition, internal structures, liquid type, sensor position and operator technique.
