A free space radar can be used as part of a liquid level interface solution. The radar cannot work alone to accomplish this. By using one of two solutions, a free space radar can solve this challenging application that stymies many solo-operating guided wave radars.
Solution #1: Free space radar with d/p level and a PLC (SCADAPack™ RTU) or DCS do the interface equation. Here, the d/p is actually calculating the interface; when coupled with radar, the level can fluctuate in a relatively normal fashion.
Solution #1: Free space radar with SCADAPack™ 4102. The SCADAPack™ 4102 Modbus™ Multivariable Transmitter has a built-in PID controller. It does the job of both a d/p level and a PLC. It generates an analog or Modbus output.
As radar becomes more popular in the marketplace (fastest-growing level technology) I believe more customers are looking for additional uses.
When guided wave radar is applied properly for interface measurement, it's great. The only issue is that there are quite a few criteria that must be met in order for the radar to operate properly. Please see this excerpt from the operating instructions from a typical guided wave radar:
Upper medium (L2)
• The upper medium must not be conductive
• The dielectric constant of the upper medium or the actual distance
to the interface must be known (input required). Min. dielectric constant: 1.6.You can find a list of dielectric constants on our home page
• The composition of the upper medium must be stable, no varying
products or mixtures
• The upper medium must be homogeneous, no stratifications
within the medium
• Min. thickness of the upper medium 50 mm (1.97 in)
• Clear separation from the lower medium, emulsion phase or detritus layer max. 50 mm (1.97 in)
• If possible, no foam on the surface
Lower medium (L1)
• The dielectric constant must be 10 higher than the dielectric
constant of the upper medium, preferably electrically conductive.
Example: upper medium dielectric constant 2, lower medium at
least dielectric constant 12.
Gas phase (L3)
• Air or gas mixture
• Gas phase - dependent on the application, gas phase does not
always exist (d2 = 0)
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