No measuring principle for level detection is equally suitable for all areas of application. It is therefore important to select the measuring system that works reliably under the application-specific conditions and at the same time withstands the economic considerations of tomorrow. The four frequencies 80 GHz, 26 GHz, 6 GHz and 1 GHz can be considered for guided and free-radiating radar technologies in a wide range of applications in all industries.

Essentially, the selection of the most suitable radar frequency for level measurement depends on three factors: the medium, its properties (e.g. foaming) and the nature of the container in which the measurement is carried out. While 80 GHz radar technology is particularly suitable for high-precision measurements in narrow containers and with large measuring ranges, 26 GHz radar is more of a generalist that also works reliably in turbulent conditions (for example in tanks, reactors and mixing vessels). The advantages of 6 GHz technology lie in its insensitivity to heavy condensation and large turbulence. The planar antenna on 6 GHz devices produces optimum measurement values in surge pipes >DN150. The guided radar in 1 GHz technology is suitable for foam-forming media or media with very low DK values; it is used for interface measurements as well as for bypass applications.

The 80 GHz radar

The 80 GHz technology, as implemented by Endress+Hauser in the 'Micropilot FMR6x', for example, is still relatively new. When using a 'DN80' antenna variant, a radiation angle of 3° is achieved here. This strong focusing enables simple commissioning, as existing installations in the application have little or no influence on the reflection signal.

The 'Micropilot FMR62' from Endress+Hauser with 80 GHz enables reliable measurements thanks to the 3° beam angle, especially in tanks with many internals.

© Endress + Hauser

The special advantages of 80 GHz technology can be clearly demonstrated by a measurement carried out in the life sciences sector during the production of pancreatin: The pancreatin is dried and stored in quarantine in a silo. This silo is narrow at the bottom, with welded seams at the transition between the cylindrical and conical parts. Previously, a free-radiating radar level measuring device with an operating frequency of 26 GHz was used here. However, due to the small distance to the container wall and strongly fluctuating adhesions of the medium at the transition to the conical part of the silo, strong interfering reflections occurred. These reflections were output as the fill level when the silo was empty. Under these conditions, reliable measurement was not possible with 26 GHz despite numerous attempts at blanking.

The situation is different with the 'Micropilot FMR62': Due to the 3° beam angle, interfering reflections on the weld seam or the fluctuating adhesions can be avoided - without blanking. The sensor reliably detects both the fill level and the empty state in the silo.

The special advantages of the 80 GHz technology result on the one hand from the high frequency of the microwave signal and on the other hand from the generation of the microwave signal using the FMCW method. Here, a microwave pulse of 76 to 80 GHz is emitted continuously. The distance to the medium is calculated from the frequency difference (Δf) between the emitted signal and the received signal.

Integrated diagnosis

In addition to considering the right frequency, the selection of suitable measurement technology is also about its impact on system availability, as unplanned downtime is expensive and disrupts operations. Endress+Hauser has developed 'Heartbeat Technology' so that devices can diagnose themselves and have a verification and monitoring function.

The range of level meters from Endress+Hauser includes variants with four frequencies: 1 GHz, 6 GHz, 26 GHz and 80 GHz.

© Endress + Hauser

It enables the current device status to be called up at any time and strategies for predictive maintenance to be installed and is integrated into many of the provider's level measuring devices. For example, the device variants of the guided radar 'Levelflex' and the free-radiating radar 'Micropilot' are equipped with Heartbeat Technology. They increase system availability through various test functions. Permanent process diagnostics and built-in diagnostic functions for the device enable a trouble-free process flow by allowing the measuring devices to issue standardized diagnostic messages and clear instructions for action before a standstill occurs. Verification takes place directly at the measuring point - without removal or process interruption. Another part of the verification is the documentation, where logs are generated automatically. The generated protocols support verification for regulations, laws and standards. This significantly reduces the amount of testing required by the user. Monitoring functions also make it possible to identify trends from the measurement data and thus to carry out simple, predictive maintenance, optimize processes and install maintenance strategies.

Communication via Bluetooth

Via Bluetooth and the 'smartBlue App', the signal progression of the free-radiating radar can be tracked on the tablet.

© Endress + Hauser

Communication via Bluetooth is an important innovation in the operation, diagnosis and maintenance of the level measuring devices. The encrypted single-point-to-point data transmission was developed in collaboration with the Fraunhofer Institute to ensure a high security standard. This password-protected remote access enables simple, time-saving commissioning for guided and free-radiating radar. By displaying the current signal curves of the corresponding radar devices via the 'SmartBlue App' from Endress+Hauser, diagnostics and maintenance can be carried out efficiently via tablet or smartphone.

Author:
Carsten Schulz is Product Manager Level at Endress+Hauser in Weil am Rhein.