Working Principle of a Non-Contacting Radar Level Transmitter

For non-contacting radar level measurement, there are two basic modulation techniques:

1). Pulse radar technology

2). FMCW (frequency modulated continuous wave) radar method

1). Pulse Radar Technology

Non-contacting pulse radar emits a microwave signal, which bounces off the product surface & returns to the sensor. The transmitter measures the time delay between the transmitted & received echo signal, and the on-board microcontroller computes the distance to the liquid surface using the formula.

Distance = (Speed Of Light X Time Delay) / 2

Once the transmitter is programmed with the tank reference height of the application, which is usually the bottom of the tank or chamber, the microcontroller calculates the liquid level.

2). FMCW (Frequency Modulated Continuous Wave) Radar Method

The FMCW radar similarly sends microwaves towards the product’s surface, but the frequency of the sent signal changes constantly.

When the signal has traveled down to the liquid surface & returned to the antenna, it is combined with the signal being transmitted at the time.

The frequency difference between the received and broadcast signals is precisely proportional to the distance to the liquid.

The frequency of the non-contacting radar can affect its performance. A lower frequency minimizes susceptibility to

  • Vapor,
  • Foam, and
  • Antenna contamination,

but a higher frequency narrows the radar beam to limit interference from nozzles, walls, & disrupting objects.

The beam width is inversely proportional to the antenna size.

As the antenna size increases, the width of the beam at a particular frequency decreases.