Understanding Guided Wave Radar Level Instruments

Guided Wave Radar (GWR)
level transmitter (Drexelbrook)

One of several technologies used for level measurement in process control is guided wave radar. A Guided Wave Radar (GWR) level transmitter combines time domain reflectometry (TDR), equivalent time sampling (ETS), and low power circuitry with a form factor that includes a wave guide extending into the contained media. TDR measures distance or level using pulses of electromagnetic energy. The pulse travels along the waveguide until it reaches the media surface and is reflected back to the unit. The speed of the pulse is known, so an accurate measure of the travel time for the signal can be processed into a distance measurement. Different media will produce a range of amplitude in the reflection, with a greater dielectric difference between air and target medium producing higher amplitude in the reflection. Industries, such as telephone, computer, and power transmission, have relied on TDR for years in order to detect and pinpoint breaks in wires or cables, making the technology more mature than it may appear by its limited timeline in level measurement applications.

ETS is used to measure the high speed, low power electromagnetic energy, and is typical when applying TDR to level measurement technology, where the signal travel distance and time are very short. The electromagnetic signals are captured by the ETS technology in nanoseconds, and are then reconstructed in the equivalent time of milliseconds. The radar scans the waveguide, collecting thousands of samples to be used in signal processing. Integrating both technologies into a single level transmitter yields an accurate and responsive instrument for process measurement.

GWR instrumentation is useful in the process control industry for its ability to measure levels in a quick, consistent way. GWR transmitters are contact radar level measurement tools, as opposed to pulsed non-contact radar transmitters that emit radar pulses through free air without a waveguide. Probes, inserted into the subject tank or vessel, serve as the waveguide for the pulsed signal. They guide the pulsed microwave vertically into the tank, providing a measure of immunity from disturbance by the tank and surrounding media. Guided wave radar technology differs from non-contact radar in a number of ways. The presence or absence of a probe is only one of them.

GWR level transmitters are used in process measurement applications throughout many industries, such as food and beverage. Tanks, pumps, and piping systems for both storage and transport can utilize GWR to continuously monitor levels. Other vessels, such as reduction, forming, mixing, heating, cooking, and cooling, can utilize GWR for similar reasons. Additionally, other stages of food and beverage manufacturing, such as centrifugation and decontamination, can be good fits for GWR technology. Guided wave radarís previous applicability in industries aside from liquid processing and implementation in a wide range of process settings show the flexibility and reliability of GWR technology.

Selecting the best level measurement technology for an application can be a challenge. Share your project requirements and concerns with a process instrumentation specialist, combining your own process knowledge and experience with their product application expertise to develop effective solutions.