Technological developments in ultrasonic level measurement have created new possibilities for applications and accurate measurement results. Various factors determine whether you should choose ultrasonic or radar.
Looking back at the first ultrasonic level meters, most were based on analog electronics and difficult to install even in the simplest applications. The biggest challenges for these sensors were often false echoes, which reflected from rods and pipes, which would exceed the echo that was actually being sought from the water surface, and which thus resulted in erroneous measurements.
Although ultrasonic measurement has been available for decades, it is only after massive investments in the development of the technology that the ultrasonic meter has gained its place as a recognized method for level measurement within the wastewater industry and other industries on the global market.
Today, in several countries, you can see pumping stations that are designed based on the advanced technology, and not least the increasing requirements for safety of the measurements required by the utility companies.
“Ultrasonic level meters have today gone from just being a level meter to being a real tool for planning service and calculating total costs for, for example, pumping stations, as well as for monitoring the duration of events at, for example, overburden edges,” says sales engineer at Aquasense Kenneth Jakobsen.
When is radar the best choice?
Reduced maintenance
Ultrasonic level meters work by activating a piezoelectric crystal to emit a pulse of ultrasound. When the pulse of sound hits objects in front of the sensor, it will send an echo back, which will reactivate the crystal. The time it takes to receive the signal again is relative to the distance to the object that reflected the sound. New developments in technology make it possible to filter out false echoes, for example from stationary objects such as pipes and concrete edges, so that only the truly desired echo is measured. This development has also meant that there are now very few applications where ultrasonic technology will not give a satisfactory result.
“The contactless technology means that there are no moving parts, which helps to reduce maintenance to a minimum. This has contributed to making ultrasonic level meters one of the preferred level measurement methods,” says Kenneth Jakobsen.
Today, ultrasonic sensors are used in many different applications, including flow measurement with weirs, sewer wells with water where level needs to be measured, or applications with pump controls, differential measurements or volume measurements in tanks.
Over the years, a lot of myths and claims have arisen around ultrasonic sensors, and one of the latest in the series is that radar measurement is superior to ultrasonic measurement. This myth is mainly due to the fact that radar has an advantage in certain types of applications. What is not mentioned is that a combination of developments in signal processing, as well as the development of low-voltage sensors with powerful acoustic signals, has meant that ultrasonic sensors can be used in approximately 95 percent of all applications. This means that even in applications with, for example, turbulence and foam, ultrasonic sensors can be used.
Advantages of ultrasonic sensors
Ultrasonic technology is a well-tested and recognized technique that has been used in applications worldwide and in many different industries. With a good ultrasonic sensor, you can expect safe and reliable level measurement time and time again.
The requirements for the sensors have also increased over time, and in one particular area there has been a major development – lower power consumption.
“Today, you can get sensors that are “loop-powered” from battery-powered data loggers, so even in applications where there is no fixed voltage supply, you can use ultrasonic level meters without frequent battery changes, which would normally have taken time from service personnel,” says Kenneth Jakobsen.
The ultrasonic level meter is thus suitable for registering overflows on flood structures, as it can be easily and simply placed in wells where there is no access to power.
Level measurement with radar
As an alternative to ultrasonic level meters, several radar level meters have been introduced to the market in recent years.
Non-contact radar technology consists of two different technologies, pulse and frequency modulated continuous wave (FMCW). Both technologies work by emitting radio frequency energy and measuring the time it takes for the signal to be returned from an object with a significantly higher dialectical constant than air. In other words, when the waves hit a hard medium, they are returned.
“The main difference between the two radar technologies is that where a radar pulse is sent out and reflected from the objects in front of it, an FMCW radar works by constantly emitting a series of radio frequency pulses at different wavelengths and measuring how quickly they are reflected back to the sensor,” says Kenneth Jakobsen.
The FMCW sensor constantly changes the frequency of the waves that are sent out, according to a mathematical formula, and thus it can easily compare the emitted waves with the received returned signals. The difference between the transmitted signal and the returned signal at the same time can be used to calculate the time it took for the signal to return, and thus provide an accurate distance to the object it was returned from.
FMCW technology is more accurate due to the often narrow spread in the signal and often stronger signal strength.
Radar vs. ultrasound
When it comes to level measurement and level control, there is really no difference between using one technology or the other. What matters is the application for which the sensor is to be used. In most cases, as a rule of thumb, an ultrasonic level sensor can meet the need.
The strong signal, which is often cited as an advantage of radar, is related to the dialectical constant of the object that returns the signal. If the medium has a low dialectical constant, but there are other elements nearby with a high dialectical constant, this can also cause interference and potentially give incorrect measurements.
An ultrasonic meter, on the other hand, only looks at the surface’s ability to reflect sound, and not at what the material is made of.
“In 95 percent of applications, an ultrasonic level sensor will be able to deliver the precise measurement that is needed. In the five percent where an ultrasonic sensor cannot deliver a satisfactory result, it is advantageous to use a radar. If you are about to make an installation and do not know whether you are best off with a radar or ultrasonic sensor, it is important that you choose a control that can work with both technologies,” says Kenneth Jakobsen.
Read more about Level radar – REFLECT™ here or contact us and hear more about level measurement.
