Radar Level Measurement

As we begin this third installment, I would like to discuss the positive and negative aspects of the Ultrasonic level sensor, in order to help us decide whether to use a radar-type level sensor.

The ultrasonic level meter, as we have already mentioned, uses a mechanical operating principle, since it displaces the medium through which it moves. It has its favorable aspects: low comparative cost, easy installation, quick configuration, defined for various working ranges, depending on the sensor used, easy maintenance, easy wiring, different types of ranges for electrical power supply, etc.

Among the drawbacks they present, one of the most important is that they are affected by suspended dust, vapors and any particulate matter in suspension, affecting the precision of work or the precision that one wants to achieve.

Each of the above leads us to look for another possibility, RADAR, which is suited to the needs of more aggressive processes with respect to particulate matter, gases, vapors or any other means of contamination, to call it something, that does not allow a free measurement between the sensor and the surface to be measured.

An important factor to consider, whether to apply it or not, is the pressure to which the sensor is subjected, MAXIMUM 3 BAR, and as a lower limit, MINIMUM 1 ATM.

Well, faced with these limitations, which only the process will reveal, we must have another alternative to be able to measure in a more aggressive environment or with other characteristics, and we arrive at the MICROWAVE o RADAR waves.

Microwave Measurement Principle

Travel time, again, is what allows us to perform a level measurement, but in this case instead of having a mechanical pulse, we will have a microwave pulse that is emitted and received by a horn.

RADAR = Radio Detection and Location

We emit a pulse of approximately 0.8 ns duration, which is transmitted and received by the trumpet. An important point to consider is that this pulse travels at the speed of light. Another important factor is its low radiation power, which is safe for both metallic and non-metallic tanks and poses no risk to people.

They are also unaffected by temperature, high pressure or vacuum conditions, the presence of dust or vapors.

An important factor to consider is the impedance of the medium reflecting the signal; this should ideally be greater than 10 mS/cm. Models exist for lower values, but never less than 1.4 mS/cm.

NOTE: There are tables that tell us the impedances of the materials to be measured, which come with each piece of equipment, depending on the brand.

The following images show a radar-type level sensor

This equipment is used where the characteristics of the process do not allow the use of an ultrasonic level sensor, since the amount of dust is much higher than normal; it should be taken into account that at a level of approximately 15 m it is no longer possible to see the bottom of the silo under normal working conditions.

This image shows the horn, where the electromagnetic wave output is concentrated. The important consideration for this equipment is that, as mentioned, the signal is electromagnetic; therefore, when dust enters the horn, there is an electrical disturbance that disrupts the measurement signal.

Therefore, the equipment has a ¼ NPT inlet, mostly for the installation of pneumatic tubing, which is fed with 15 PSI for the purpose of having an air supply from the inside to the outside, that is, a pressurization of the horn and expelling the air, preventing dust from entering its interior and causing electrical noise.

Cleaning the equipment is paramount, but only its internal components. The equipment is sealed and lacks local indication, relying solely on remote monitoring. This is for extreme applications.

I hope this information has been helpful regarding these devices. For any questions or inquiries, please write to:

Email: hcarrasco@instrumentacionycontrol.net

Twitter: @instrumentacion