SPECIALIST EQUIPMENT
Bigger, faster, stronger – better?
Radar-based level measurement instrumentation has experienced a constant rise in the radar frequencies used. But does more always equal better?
W
ithin this interview, Andrew Reese, global industry manager for Primaries & Metal at Endress+Hauser, explains why the answer to
the above question is not a simple “yes” or “no”.
Could you explain what impact the frequency has on radar level measurement in general?
Andrew Reese: First and foremost it’s a matter of simple physics; the frequency infl uences the wavelength of the measuring signal. T e higher the frequency, the shorter the wavelength, that means the shorter the distance between two wave crests.
And how does this infl uence the measurement and the suitability for diff erent applications?
AR: For example, with a higher frequency the microwave beam angle can be much smaller. A narrow beam of only 3° can measure down in to the bottom cone of a silo and is an advantage for level measurement in tall narrow tanks with many obstacles inside, such as strengthening
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Does a higher frequency also have disadvantages?
AR: Yes. For example, a high-frequency signal is more prone to attenuation due to the small wavelength, which means it loses strength when crossing through a medium. In practice this results in high frequency instruments having more trouble with conditions such as dust, foam or vapour. But ripples and waves on liquid mediums can also be a problem - because on such turbulent surfaces the signal tends to get disturbed and scattered. If the wavelength of the signal is smaller than the wavelength of the waves on the surface, that is. If the signal is scattered, however, it also loses power and makes the measurement more unreliable.
So, what is the ideal frequency?
AR: T ere is no one best frequency for radar level measurement. It all depends on the
beams, struts, ladders or an aeration system. Also, a higher frequency signal will work reliably on both very small chemical additive tanks and very tall silos compared to lower frequency signals.
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