Guided Wave Radar Pros and Cons

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Guided Wave RadarPros and Cons

• By David Land, P.E.
• ConocoPhillips
• Field Instrumentation Network Lead

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GWR Cons First

• GWR is a contacting technology the probe is
  in the process fluid. If the fluid is
  particularly corrosive or there are material
  compatibility issues this can become a limiting
  factor. There are alternate metals available for
  probes and Teflon coating is an option, but with
  Teflon coating you run into Temperature issues.
• The maximum process temperature for most units is
  around 750 F. Temperatures over this require a
  different technology.
• GWR is unpredictable in foaming applications. In
  light foam the GWR will ignore the foam and
  reflect back the liquid level. In heavy foam, the
  signal can be absorbed and reflect back the top
  of the foam as level and/or weaken the overall
  signal.

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GWR more Cons

• Highly viscous fluids should be approached with
  caution. They tend to coat the probe. Single
  probes work well with coating, but heavy coating
  will weaken the signal. Dual probes and coax
  probes can strengthen the signal but can also
  bridge in coating service meaning the fluid
  will bridge across the two probes or inside the
  pipe of a coax and cause the signal to lock on
  the bridging as the level.
• Tanks with agitators or extreme turbulence should
  be approached with caution. If the agitator hits
  the probe it will cause a false signal. Extreme
  turbulence can either break a rigid probe or
  cause a flex probe to hit against the nozzle,
  causing a false signal. A coax probe or bridle is
  a good solution for turbulence as long as the
  process media does not plate out or coat metals.
• Interface applications where the product
  dielectrics are not at least 10 apart will not
  work with GWR, since GWR depends on a difference
  in dielectric to reflect back the interface
  level. Oil/Water is the ideal interface
  application water with a dielectric of 80,
  oil with a dielectric of approx. 2. They are
  much more that 10 apart.

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GWR more Cons

• Fiberglass or plastic tanks should be approached
  with caution. The GWR requires a solid ground for
  the microwave signal on the probe. We have
  successful installations on Fiberglass, but dual
  probes or a metal flange at least 2 OD for a
  mounting surface is recommended.
• In interface applications, if the dielectric
  constant of the upper product varies there can be
  an error in the measurement. The dielectric of
  the upper product must be lower than the
  dielectric of the lower product to have an
  interface reflection. The upper product cannot
  have a dielectric greater than 10 for the
  single probe and 5 for a dual probe. Depending
  on the probe, the upper product must be at least
  4-8 for the radar to distinguish the echoes
  between the two fluids.
• Emulsion layers between two liquids can cause
  some inaccuracies.
• Longer probe lengths may require a crane to
  extract from the vessel.

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GWR Pros

• Direct level measurement
• No moving parts
• Handles changing density, dielectrics,
  conductivity, temperature, pressure, pH and
  viscosity
• Handles small tanks, difficult tank geometry,
  interfering obstacles
• Easy swap (small openings)
• Virtually unaffected by dust, vapor and
  turbulence

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GWR Pros

• Solids, powders, granules
• Level and Interface Level from one transmitter
• Guided Wave Radar technology is virtually
  unaffected by probe coating
• Recalibration not necessary
• Recalibration cost dramatically reduced
• Measurement availability improved

7
GWR Pros

• Reducing CAPEX Cost
• Low installation cost
• Installation while tank is in service
• Easy Commissioning
• Pre-configured transmitters
• No re-calibration required
• User-friendly Configuration tools

8
GWR Pros

• Reducing OPEX Cost
• Increased Availability
• No re-calibration
• Entire tank range
• Advanced Signal Processing
• No moving parts less down-time
• Increased Safety, Health Environment
• Dual Compartment
• Configuration adjustments without opening tank
• One point entry on top of tank

9
GWR Pros

• Reducing OPEX Cost
• Reduced Operations Maintenance
• No matching parts
• No moving parts, less spare parts, less
  maintenance
• Remove electronics while tank is in service
• Easy troubleshooting
• Higher Quality
• Reliable, accurate level measurement
• Virtually unaffected by process conditions