The New LW radar level sensor

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The New LW radar level sensor
Non-contact free radar level sensing provides high accuracy measurement up to 10 m (33 ft)

Principle of operation
The device works according to the FMCW (Frequency Modulated Continuous Wave) method. Electromagnetic pulses in the GHz range are sent to the medium at a constantly changing frequency between 77 and 81 GHz. Since the transmitter continuously changes the frequency of the transmitted signal, there is a frequency difference between the transmitted and the reflected signal. The frequency difference between the transmitted and received signals over a fixed time period is processed using FFT evaluation resulting in fast, reliable and very accurate level measurements. The math is complex, but the powerful microprocessor onboard the LW performs the calculations quickly with response time under 350 msec and accuracy of +/- 2 mm over the entire measuring range.

Advantage of 80 GHz frequency
Antenna size and frequency are the two main factors that determine the range, resolution, and accuracy of a radar sensor. The smaller the antenna, the bigger the radar opening angle, and the higher the frequency the lower the wavelength. As illustrated in the image of the frequency ranges, this means the high frequency 80GHz technology provides a comparatively small opening angle for the antenna size. 

  • The higher frequency signal increases bandwidth and resolution to provide accurate and repeatable measurements. 
  • Smaller beam angle results in a more focused radar signal capable of detecting lower dielectric media and avoiding obstacles in the tank 
  • Lower wavelengths reduce the antenna size which allows us to maintain a compact design, reducing weight and overall size of the sensor. 

Stronger signal, less interference
In practice, the strong signal-focusing generated by the small opening angle enables measurement of low dielectric media, as the high focus increases the reflection to the sensor. In addition, the high level of focus prevents obstacles such as agitators or spray balls from being detected and causing signal interference.

High-resolution, precise level detection over the entire tank height
In applications such as industrial level detection, measurement accuracy to the millimeter is of the utmost importance. How precisely a measurement is made and how high the resolution of the distance is (i.e. how precisely level changes are detected) depends on the bandwidth of the transmitted frequencies. The wide bandwidth available in the 77 to 81 GHz band ensures measurements are very accurate. 80 GHz radar sensor can achieve 20x better performance in range resolution and accuracy compared to a 24 GHz radar. In addition, the high resolution helps to separate the liquid level from unwanted reflections at the bottom of the tank. This enables the sensor to accurately measure the liquid level over the entire tank height and minimize the dead zone at the bottom of the tank. The high signal resolution also improves the minimum measurable distance providing reliable level measurement right to the top of the tank.

With IO-Link, the LW free radar sensor can provide:

  • Higher measurement resolution than analog without scaling (1mm steps up to 15 m)
  • Internal device temperature of the sensor
  • Measured power supply voltage
  • Current device status and diagnostic information including signal strength (Good, Degraded, Bad) and cleaning required alert
  • Automatic device replacement
For more information on IO-Link: Discover IO-Link

 

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