Emerson Process Management 5300 Flexible Single Lead Product, Upper product dielectric constant

Reference Manual

00809-0100-4530, Rev BA July 2009

Rosemount 5300 Series

Figure 2-9. Maximum Upper Product thickness for the Flexible Single Lead probe.

For measuring interface level, the transmitter uses the residual wave of the first reflection. Part of the wave, not reflected at the upper product surface, continues until it is reflected at the lower product surface. The speed of this wave depends fully on the dielectric constant of the upper product.

To measure interface, the following criteria have to be fulfilled:

•The dielectric constant of the upper product must be known and should be constant. The Rosemount Radar Master software has a built-in dielectric constant calculator to assist in determining the dielectric constant of the upper product. (see “Dielectric Constant/Dielectric Range” on page 5-23)

•The upper product must have a lower dielectric constant than the lower product to have a distinct reflection

•The difference between the dielectric constants for the two products must be greater than 6

•The maximum dielectric constant for the upper product: 10 for the coaxial probe, 7 for the twin lead, and 8 for the single lead probes

•The upper product thickness must be greater than 5.1 in. (0.13 m) for all probes, except the HTHP coaxial probe, which requires 8 in. (0.2 m), to distinguish the echoes of the two liquids

The maximum allowable upper product thickness/measuring range is primarily determined by the dielectric constants of the two liquids.

Target applications include interfaces between oil / oil-like and water / water-like liquids with a low (<3) dielectric constant for the upper product and a high (>20) dielectric constant for the lower product.

For such applications, the maximum measuring range is limited by the length of the coaxial, rigid twin, and rigid single lead probes.

For flexible probes, the maximum measuring range is reduced by the maximum upper product thickness, according to the diagram below. However, characteristics may vary between the different applications.

	115	(35)		Flexible Single Lead
Product	98	(30)
	82	(25)				80	Lower product
					40		dielectric constant
MaximumUpper Thickness,ft (m)	66	(20)			20
					10
	49	(15)
	33	(10)
	16 (5)
		0
		1	3	5	7		9	11

Upper product dielectric constant

2-13