Has anyone experienced a radar gauge drifting? We have several radar gauges on several H/C tanks. Some of the radars are drifting by several inches (nothing to do with strapping table etc.) In one case we have two radars on one tank. One is stable, the other drifts even though the gauges are identical.

These gauges happen to be ohmart-vega which I have used many times in the past with no problems. Coincidentally, some Saab radars work fine elsewhere on the tank farm (it's just the cost that I have trouble with)

Any suggestions as to what I might look for?

 

The drift happened due to your dielectric of the medium is too low for hydrocarbon. The signal evaluation is not stable. There for you level will slowly penetrate the medium especially at low level and cause the measuring error.

You hae to raise you empty distance higher (e.g 0.5 meter) or install the radar in a stilling well if possible. However, make sure the gap between the antenna horn and stilling well is kept at very close, 1mm gap is ideal case.

The saab signal might be higher (depending on model) that is why it work well.

 

The earlier comment is right on the money - return signal strength is directly proportional to fluid dielectric and inversely proportional to distance. A larger horn will increase the return signal strength (which is probably why the Saabs work so well) at any given distance, the stilling well mentioned earlier will do the same.

If you have a rod-type antenna you will probably have to replace the instrument. If a horn-type, a field retrofit to a larger horn is probably both possible and inexpensive. However, you may find that the optimal horn diameter is larger than any available nozzel in the vessel. In this case you have to install the horn from the inside.

One caution. Most radar vendors offer TDR/MIR guided microwave level instruments which they may present as a candidate solution. However, the physics of both measurements are so I would expect similar results.

 

Mr Yan's comment is one of two possible installation mods that would improve the strength of the return signal. The other would be to increase the diameter of the horn (this is why your Saabs work so well). In some cases the required diameter exceeds any available vessel nozzel diameter so the change must be made from inside the tank.

Beware. Most vendors with a radar gauge also offer a TDR technology that may appear to be a solution. However, the physics of the two measurements are similar (both reflect at a dialectric interface, in this case between air and liquid) and my expectation is that if the dialectric difference is too low for one technology it will hold true for the other.