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Manual Supplement
00809-0200-4853, Rev AB
Rosemount 3051S Series Pressure Transmitter
November 2017
Rosemount 3051S Series Pressure Transmitter
When the lines between the process and the transmitter start to plug through fouling and build-up on
the inner surfaces of the impulse tubing or loose particles in the main flow getting trapped in the
impulse lines, the time and frequency domain signatures of the noise start to change from their normal
states. In the simpler case of a Pressure measurement, the plug effectively disconnects the Pressure
transmitter from the process. While the average value may remain the same, the transmitter no longer
receives the noise signal from the process and the noise signal decreases significantly. The same is true
for a DP transmitter when both impulse lines are plugged.
The case of the Differential Pressure measurement in a flow application with a single line plugged is more
complicated, and the behavior of the transmitter may vary depending on a number of factors. First the
basics: a differential pressure transmitter in a flow application is equipped with two impulse lines, one on
the high pressure side (HP) and one on the low pressure side (LP) of the primary element. Understanding
the results of a single plugged line requires understanding of what happens to the individual pressure
signals on the HP and LP sides of the primary element. Common mode noise is generated by the primary
element and the pumping system as depicted in Figure 14. When both lines are open, the differential
pressure sensor subtracts the LP from the HP. When one of the lines are plugged (either LP or HP), the
common mode cancellation no longer occurs. Therefore there is an increase in the noise of the DP signal.
See Figure 15.
Figure 14. Differential Pressure Signals under Different Plugging Conditions
Figure 15. Differential Pressure (DP) Signals under Different Plugged Conditions
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