Emerson 3051S Dokumentacja Pobierz pdf (Strona 96)

Reference Manual

00809-0200-4801, Rev CA

July 2010

Rosemount 3051S

6-18

Figure 6-16. Basics of Plugged

Impulse Line

Testing at Emerson Process Management and other sites indicates that

Statistical Process Monitoring technology can detect plugged impulse lines.

Plugging effectively disconnects the transmitter from the process, changing

the noise pattern received by the transmitter. As the diagnostic detects

changes in noise patterns, and there are multiple sources of noise in a given

process, many factors can come into play. These factors play a large role in

determining the success of diagnosing a plugged impulse line. This section of

the product manual will acquaint users with the basics of the plugged impulse

lines and the PIL diagnostic, the positive and negative factors for successful

plugged line detection, and the do’s and don’ts of installing pressure

transmitters and configuring and operating the PIL diagnostic.

Plugged Impulse Line

Physics

The physics of Plugged Impulse Line Detection begins with the fluctuations or

noise present in most Pressure and Differential Pressure (DP) signals. In the

case of DP flow measurements, these fluctuations are produced by the

flowing fluid and are a function of the geometric and physical properties of the

system. The noise can also be produced by the pump or control system. This

is also true for Pressure measurements in flow applications, though the noise

produced by the flow is generally less in relation to the average pressure

value. Pressure level measurements may have noise if the tank or vessel has

a source of agitation. The noise signatures do not change as long as the

system is unchanged. In addition, these noise signatures are not affected

significantly by small changes in the average value of the flow rate or

pressure. These signatures provide the opportunity to identify a plugged

impulse line.

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.

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Emerson 3051S Dokumentacja Strona 96