Guided wave radar (GWR) is also called time domain reflectometry (TDR) or micro-impulse radar (MIR).
Basic principle
In a Guided Wave Radar installation, the GWR is mounted on the top of the tank or chamber, and the probe usually extends to the full depth of the vessel. A low energy pulse of microwaves, travelling at the speed of light, is sent down the probe. At the point of the liquid level (air / water interface) on the probe, a significant proportion of the microwave energy is reflected back up the probe to the transmitter.
The transmitter measures the time delay between the transmitted and received echo signal and the on- board microprocessor calculates the distance to the liquid surface using the formula:
Distance = (Speed of light x 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.
The basic equation for measuring the tank level is
Level = Tank Height – Distance
Because a proportion of the pulse will continue down the probe through low dielectric fluids, a second echo can be detected from an interface between two liquids at a point below the initial liquid level.
This characteristic makes guided wave radar a good technique for measuring liquid/liquid interfaces such as oil and water and measuring through some foams.
Guided wave radar can be used in vessels with tight geometry, in chambers, and in tanks of all sizes. Advanced GWR also works well in low dielectric and turbulent applications. Because it is not dependent on reflecting off a “flat” surface, it works well with many powders and grains as well as liquids with slanted surfaces caused by vortices.
Guided wave radar technology Benefits
Advantages
Limitations
While guided wave radar works in many conditions, some precautions need to be taken with respect to probe choice. Several probe styles are available and the application, length, and mounting restrictions influence their choice. Unless a coax-style probe is used, probes should not be in direct contact with a metallic object, as that will impact the signal. If the application tends to be sticky or coat, then only single lead probes should be used. Some advanced GWRs on the market have advanced diagnostics, with the ability to detect build-up on the probe. Chambers with a diameter less than 3 in. (75 mm) may cause problems with build-up and may make it difficult to avoid contact between chamber wall and probe.
Learn the example of flip-flop PLC program for lamps application using the ladder logic to…
In this article, you will learn the STAR DELTA programming using PLC controller to start…
Lube oil consoles of rotary equipment packages in industrial process plants are usually equipped with…
Rotating equipment packages such as pumps, compressors, turbines need the lube oil consoles for their…
This article explains how to blink lights in ladder logic with a detailed explanation video…
In this article, a simple example will teach you the conversion from Boolean algebra to…