Emerson Process Management ROSEMOUNT 5300 - Manual (Page 27)

Reference Manual
00809-0100-4530, Rev BA
July 2009
2-13
Rosemount 5300 Series
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.
Figure 2-9. Maximum Upper
Product thickness for the
Flexible Single Lead probe.
1 3 5 7 9 11
0
16 (5)
33 (10)
49 (15)
66 (20)
82 (25)
98 (30)
115 (35)
80
40
20
10
Upper product dielectric constant
Max
imu
m Up
per Prod
uct
T
h
ickn
ess, f
t (
m
)
Lower product
dielectric constant
Flexible Single Lead