3 Highly Accurate And Reliable Ways To Measure Fluid Level
In our overview of fluid level measurements, we looked at devices ranging from the simplest to the more advanced, and the different advantages and limitation of these. This article outlines three of the most cost-effective and reliable fluid level measurement devices that allow greater efficiencies all round, namely ultrasonic, radar and capacitive.
1. Ultrasonic level devices
With ultrasonic level measurement, a sensor emits electronic pulses in the direction of the surface, which then transmits them back. The time that the ultrasound pulse takes from emission to reception at surface level is proportionate to the fluid level in the tank.
This simplicity makes them ideal for standard applications, from liquids to solids. They’re also easy to install on empty or full storage tanks and can be set up in minutes. Probably the biggest advantage is that they are no-contact and have built in temperature compensation, requiring little to no maintenance. Despite alterations in chemical composition, ultrasonic level devices offer precise readings. Level measurement is thus not affected the type of liquid, temperature (although its construction materials limit temperatures to around 70°C), process pressure (3 bar usually depending on materials), or variability in density or viscosity.
Ultrasonic sensors are suitable for liquids or dry products. However, as the speed of sound can vary depending on any gas mixtures present, it is important to know if there are any gases present in the tank before using ultrasonic level measurement technology.
2. Radar transmitters
Radar transmitters or sensors (also known as through-air or open-air radars) send out a radar (microwave) signal that bounces off the surface before returning to the sensor. The sensor measures the time between the transmitted and received signal (total round trip time) and an on-board microprocessor calculates distance to liquid level. The key element of radar transmitters is the dielectric contact of liquid – the reflected energy at microwave (radar) frequencies depends on the fluid’s dielectric constant.
Guided wave radar (GWR) transmitters are even more accurate as they have a focused energy path. A rigid probe or flexible cable guides the microwave signal from the top of the tank to the liquid level and back to the sensor.
Guided wave radar allows most of the benefits and few of the liabilities of open-air, ultrasound, and even laser systems. The wave speed of guided radar is mostly unaffected by changes in pressure, temperature and vapor conditions, ensuring accuracy of measurements.
Guided wave radar sensors don’t need any calibration as they work in a vacuum. As the wave follows a probe or cable, issues such as beam-spread and false echoes from the tank’s walls are prevented. As they have no moving parts, little maintenance is needed. Guided wave radar can be used when liquids form heavy vapours, for corrosive and dirty applications as well and dry product applications.
3. Capacitive sensor
A capacitive liquid level sensor is a device used to measure the height of a liquid and convert it to an electrical signal to control or monitor the liquid level. They usually have a single probe immersed inside the tank which acts as an electrode. This probe interacts with an electrode usually placed in the wall of the tank opposite, and the two connect to form a capacitor.
The liquid content of the tank is the dielectric medium, which affects the capacitance between the two electrodes. If the level or the liquid increases or decreases, this changes the capacitance measured by the probe in a predictable manner, which makes the capacitive sensor an effective measurement of liquid level.
Capacitive sensors are useful for liquids, powdered and granular solids, liquid metals at high temperatures and liquefied gases at low temperatures. They are resistant to turbulence and can handle corrosive materials and high-pressure industrial applications. Mechanically simple, capacitive sensors are easy to adapt for different vessel sizes and have no moving parts, which means little maintenance. Some disadvantages include sensitivity to changes in environmental conditions, errors caused by coatings and the fact that applications with larger particle sizes can have low dielectric constants.
It’s important to understand the uses of different level measurement systems as well as the limitations of each before choosing a liquid level sensor. For information on what level measurement sensor we recommend for your specific requirements, call our toll-free number 1-800-367-4180. We have experts on hand to help you choose, install, and maintain a variety of equipment. And to answer questions about things you’ve previously tried gone wrong.