Do you know which radar level technology is best for tank gauging in custody transfer applications? Is it FMCW or Pulsed Time of Flight? Selecting the wrong instrumentation can cost customers up to hundreds of thousands of dollars annually, not because of the price of the instrumentation but due to less accurate Inventory Measurement that leads to unnecessary product losses.
What’s the Difference?
Frequency modulated continuous waveform (FMCW) and Pulsed Time-of-Flight (PToF) are the two technologies used in modern radar-based tank gauging instruments, and there is often confusion about which is best. However, both technologies are proven in many applications and both meet the stringent requirements for <1mm high-accuracy level measurement. So, what is the difference between FMCW and PToF?
FMCW radar transmits continuously, with the radar signal reflecting off the liquid surface received by the antenna. The shift in the frequency is then used to calculate distance to the liquid. PToF radar transmits energy in the form of a pulse which reflects off the liquid surface and is received by the antenna. The time it takes for this to happen is used to calculate the distance to the liquid. Essentially, there are no significant differences between the two technologies except for the algorithm used to calculate level. Selecting a radar level instrument, then, is more about the beam angle and the intended application.
Importance of Beam Angle
Beam angle is important because it determines how close the radar device can be installed to the tank wall. The beam should never reach the tank wall because it will interfere with the radar signal resulting in an inaccurate level measurement. A narrow beam angle allows the instrument to be installed close to the tank wall making it easier to avoid obstacles as well as service and maintain in the future. There are advantages to wide beam angles in tanks wit waves and agitation and are best when measuring through steam or vapors.
Tank gauging applications require a level instrument with extremely high accuracy and both PToF and FMCW methods meet the stringent regulations in the oil industry, but great care should be taken when selecting the devices used for your inventory management.
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