The biggest challenge plants have for process instrumentation is level measurement. Pressure, temperature and flow all seem to be addressed well but level continues to be a problem. This post is a reprise of previous posts, but given the number of challenges involving level, I think it worth another look. While differential pressure (DP) level is the most commonly installed level measurement technology, it will be surpassed with radar. Radar level measurement is considered the best practice.
There are two kinds of radar that are used for process level measurement. These are guided wave radar (GWR) and non-contact radar. As the names suggest, GWR uses a rod or cable to “guide” the radar energy while non-contact radar has a cone or rod antenna that does not touch the product surface. In many applications, both technologies could be applied. I have tried to outline the best practices for both.
Guided wave radar should be your first choice for level measurement. If you have a clean process fluid, it provides the most reliable measurement. Because the radar energy is guided, there is not a loss of signal. GWR is great for turbulence and foam. There are numerous waveguide configurations which address many different applications. It is less expensive than non-contact radar and not as limited in terms of installation considerations. With advanced diagnostics, like Signal Quality Metrics, any problems, like buildup, can produce an alert. There are also application specific features like Probe End Projection for low dielectric fluids and Dynamic Vapor Compensation for high dielectric vapors (an echo at a known distance is the secret) that cannot be done with non-contact radar.
Personally, I am a fan of non-contact radar. It is radar and it is non-contact. I realize this is a contradiction from above, but it is a personal preference. With non-contact radar you should use the largest antenna possible. The larger the antenna, the tighter the beam angle. This allows for more energy to be reflected and detected. There are high- and low-frequency versions which offer benefits for different applications. High frequency should be used, if possible, as the beam angle is smaller. However, agitation, turbulence and high vapor density require the use of a low frequency device. The drawback is low-frequency radar requires a larger cone for the same beam angle. As with GWR there are several antenna options which create a solution for a number of applications.
Of course, there are applications where radar level measurement just won’t work. The process is hot, sticky, turbulent and has a considerable amount of vapor. A nuclear level technology should be used for this. The sources are much lower in terms of radiation than previous generations. The detectors are lighter and easier to work with. Much more support is given for NRC compliance.
As level measurements continue to be a challenge, radar level technology will continue to improve. Transmitters are able to transmit and receive more energy. Algorithms continue to be developed to improve signal processing. Soon, level measurements will be as easy as pressure, temperature and flow. Radar level will be the technology of choice.
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