Guided Wave Radar(GWR) is a contacting type continuous level measurement instrument. Also called Time Domain Reflectometry (TDR). A Guided Wave Radar consists of a probe with a full length of the tank and the transmitter connected to the probe is mounted at the top of the tank. The system is shown below.
A low energy pulse of microwave/electromagnetic wave is sent down through the probe. The sent microwave is travel to the bottom of the tank with a speed of light. A proportion of the wave is reflected back to the transmitter from the surface of the liquid-air contact. The proportion of the wave reflected depends on the liquid filled in the tank.
The "time of flight" of the wave is measured and which will be in relation to the level of the tank. That is the time delay between the transmitted and received signal is measured by the onboard microprocessor and calculate the distance to the liquid surface.
Distance = (speed of light * time delay)/2
Once the transmitter is programmed with the reference gauge height of the application – usually
the bottom of the tank or chamber – the liquid level is calculated by the microprocessor.
Types of Probe available:
The single-element probe: Less efficient, But widely used because most forgiving in design
The Twin-element probe: General purpose-probe used in long-range applications.
Coaxial probe: Most efficient, similar to standard coaxial cable. Used for low dielectric applications.
Advantages of the GWR:
Accurate and more reliable in level measurement
GWR can be used with liquid contain sludges, slurries, and solid content.
Change in density, viscosity, dielectric and conductivity of the fluid will not affect the measurement.
Pressure, temperature and vapour space have no impact on measurement.
GWR is easy to install even if there are another level measuring technologies install in tank such as displacers.
And easy to install even if there is liquid in the tank.