Emerson 3051S Dokumentacja Pobierz pdf (Strona 106)

Reference Manual

00809-0200-4801, Rev CA

July 2010

Rosemount 3051S

6-28

First SPM needs to be configured to monitor the pressure as described in

“SPM Configuration for Monitoring Pressure” on page 6-6. After SPM has

been configured, the standard deviation needs to be trended, either in an

EDDL-supported host (such as AMS Device Manager, shown in Figure 6-22),

or in the DCS as described in “Trending Statistical Values in Control System”

on page 6-10.

Figure 6-22. Trend of Standard

Deviation in AMS Device

Manager

After configuring SPM, wait long enough for the SPM to begin updating the %

change in standard deviation. This will take at least 2-3 times the SPM

Monitoring Cycle.

While the standard deviation is being trended, the impulse line valve (e.g.

manifold or root) must be manually closed. After the impulse line is closed off,

note in the SPM trend how much the standard deviation has changed. In the

example in Figure 6-22 the standard deviation has increased by 49.9%.

This process needs to be repeated for each impulse line plugging condition

that needs to be detected. For DP measurements, this should be done for

both the high side and the low side impulse line. Optionally, you may also wish

to do this for both sides plugged. For GP/AP measurements, this process

would be done only for the single impulse line.

Upper and lower detection limits are chosen based on the degree of standard

deviation change that was observed when the impulse lines were plugged.

These limits should be less than the observed change in standard deviation,

but more than changes in standard deviation that happen under normal

process conditions. A lower detection limit will result in a plug being detected

earlier and more often, but could also lead to false detections. A higher

detection limit will reduce the likelihood of false detections, but also increase

the probability that an impulse line plug will not be detected.

A good “rule of thumb” is to set the detection limit to half of the observed

change in standard deviation, but no less than 20%

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Emerson 3051S Dokumentacja Strona 106