Radar Level Time of Flight Calculator
Understand how radar level transmitters turn echo time into level. Convert time of flight to distance and level, and see the effect of the medium on guided wave radar interface measurement.
- c = c₀ ÷ √εr = 299,792,000 m/s
- d = c × t ÷ 2 = 2.9979 m
- Level = reference height − d = 3.0021 m
Radar Time of Flight
Level = Href − d
c₀ = 299,792,458 m/s. In air and most vapours εr ≈ 1. Below an oil layer in guided wave radar interface measurement, the pulse slows by √εr of the oil.
Worked example
An echo returns after 20 ns: d = 3 × 10⁸ × 20 × 10⁻⁹ ÷ 2 = 3.0 m. With a 6 m reference height, the level is 3.0 m.
Frequently Asked Questions
How does a radar level transmitter measure level?
It sends microwave pulses or a frequency sweep to the surface and measures the time or frequency shift of the echo, which gives distance.
What is the effect of the dielectric constant?
Low εr liquids reflect weakly, making the echo small. For guided wave interface measurement, εr of the upper layer also sets the speed in that layer.
Does vapour or pressure affect radar?
Very little for most applications. Only dense vapours such as high pressure steam slow the signal noticeably.
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