Emerson Process Management 5300 manual Probe END Projection, Probe End pulse

Rosemount 5300 Series

Reference Manual

00809-0100-4530, Rev BA July 2009

PROBE END PROJECTION

Probe End Projection allows you to measure product level when the surface pulse is too weak to be detected. For example, long measuring range and products with very poor reflectivity (low dielectric constant).

A product with very low reflectivity is characterized by its low dielectric constant. Such a product reflects relatively small amounts of the microwave energy emitted from the Rosemount 5300 transmitter, and most of it is transmitted through the product. Consequently, situations may occur where the surface pulse is invisible to the transmitter at long measuring ranges. The Probe End Projection function in the Rosemount 5300 transmitter makes it possible to carry out accurate measurements even under such circumstances.

When the microwaves emitted by the Rosemount 5300 transmitter propagate through the product in the tank, the Probe End pulse appears to be located below the actual probe end. The apparent displacement of the Probe End pulse is a consequence of the reduced propagation speed of the measurement signal through the product compared to the speed through air. The displacement of the Probe End pulse can be observed by using the Echo Curve Analyzer in the Rosemount Radar Master (see “Using the Echo Curve Analyzer” on page 7-10).

For products with very low dielectric constants the product surface level can be determined by comparing the actual probe end position as given by the Probe Length value, with the apparent position of the Probe End pulse. The difference is related to the properties of the product, i.e. the Dielectric Constant, and the distance D travelled by the measurement signal through the product, see Figure C-8.

Figure C-8. The properties of the product makes the probe end pulse appear to be below the actual probe end.

Surface pulse is missing due to low product reflectivity

Probe End pulse

Note! It is important that the Probe Length and product Dielectric Constant are given with high accuracy.

The product Level is given by the relation between Probe End displacement Δ, the

Dielectric Constant of the product, and distance D

D

Actual Probe

End position

Δ

Apparent Probe

End position

C-10