Emerson Rosemount 3051 CF Series, Reference Manual

Page: 134 / 146

Figure 7-10: Differential Pressure (DP) Signals under Different Plugged Conditions
A. Both lines open
B. HP line clogged
C. Both lines clogged
However, there is a combination of factors that may affect the output of the DP
transmitter under single plugged line conditions. If the impulse line is filled with an
incompressible fluid, no air is present in the impulse line or the transmitter body, and the
plug is formed by rigid material, the noise or fluctuation will decrease. This is because the
combination of the above effectively
stiffens the hydraulic system formed by the DP sensor
and the plugged impulse line. The PLD diagnostic can detect these changes in the noise
levels through the operation described previously.
7.6.3 Plugged line detection factors
The factors that may play a significant role in a successful or unsuccessful detection of a
plugged impulse line can be separated into positive factors and negative factors, with the
former increasing the chances of success and the latter decreasing the chances of success.
Within each list, some factors are more important than others, as indicated by the relative
position on the list. If an application has some negative factors, that does not mean that it
is not a good candidate for the diagnostic. The diagnostic may require more time and
effort to set up and test, and the chances of success may be reduced. The following
sections discuss each factor pair.
Ability to test installed transmitter
The single most important positive factor is the ability to test the diagnostic after the
transmitter is installed and while the process is operating. Virtually all DP flow and most
pressure measurement installations include a root or manifold valve for maintenance
purposes. By closing the valve, preferable the one(s) closest to the process to most
Advanced pressure diagnostics Reference Manual
July 2020 00809-0100-4774
134 Rosemount 3051