Of the two operational technologies in common use today, Magnetrol utilizes Pulse Burst Radar rather than frequency modulated continuous wave (FMCW) for Radar level measurement. Pulse Burst Radar operates in the time domain and does not require the complex and expensive processing required to enable FMCW.
Because echoes are discrete and separated in time, Pulse Burst Radar is more efficient at sorting through extraneous echoes and selecting the one reflected by the true level. Pulse Burst Radar also has excellent averaging characteristics, important in those applications where a return signal is affected by factors described below in “The Three D's of Radar”.
Unlike true pulse devices that transmit a single, sharp (fast rise-time) waveform of wide-band energy, Pulse Burst Radar emits short bursts of 6 GHz or 26 GHz energy and measures the transit time of the signal reflected from the liquid surface. Distance is then calculated utilizing the equation:
Distance = C x Transit Time/2, (where C = Speed of Light)
The level value is then developed by factoring in tank height and other configuration information. The exact reference point for distance and level calculations is the sensor reference point – the bottom of an NPT thread, top of a BSP thread, or face of a flange.
The three Ds of radar
Radar applications are influenced by three basic conditions:
The Dielectric of the process medium;
The Distance, or measuring range of the application; and
A variety of Disturbances that may attenuate or distort the radar signal.
Low dielectric media can weaken radar's return signal and thus shorten a device's effective measurement range. Pulse Burst Radar provides accurate measurement even for low dielectrics; however, in instances where the dielectric is extremely low, as is the case with liquid gas, fuels and solvents, or where boiling and/or flashing can exist, Guided Wave Radar (GWR) may be the better choice in radar technology.
The distance, or measurement range, of Pulse Burst Radar is a function of the type of antenna selected, the dielectric constant of the media, and the presence of signal interference. Disturbances caused by turbulence, foam, false targets (interior tank obstructions causing false echoes), multiple reflections (reflections from off the tank roof), or a high rate of level change, can weaken, scatter, or multiply radar signals. Very high and very low liquid levels can also be problematic.