Loop Integrity; Introduction - Emerson Rosemount 3051S Series Reference Manual

Reference Manual
00809-0100-4801, Rev HA
Table 7-7. Possible Process Intelligence and Plugged Impulse Line diagnostic Issues and
Process Intelligence diagnostic issue
Diagnostic status indicates insufficient
variability and will not leave learning or
verifying mode
Diagnostic will not leave verifying mode
Diagnostic does not detect a known
condition
Diagnostic indicates "High Variation
Detected" when no diagnostic event has
occurred
7.4

Loop Integrity

7.4.1

Introduction

The Loop Integrity diagnostic provides a means to detect issues that may jeopardize the integrity of the
electrical loop. Some examples are: water entering the wiring compartment and makes contact with the
terminals, an unstable power supply nearing end of life, or heavy corrosion on the terminals.
This technology is based on the premise that once a transmitter is installed and powered up, the
electrical loop has a baseline characteristic that reflects the proper installation. If the transmitter
terminal voltage deviates from the baseline and outside the user configured threshold, the Rosemount
3051S with Advanced HART Diagnostics can generate a HART alert or analog alarm.
To make use of this diagnostic, the user must first create a baseline characteristic for the electrical loop
after the transmitter has been installed. The loop is automatically characterized with the push of a
button. This creates a linear relationship for expected terminal Voltage values along the operating region
from 4–20 mA. See
Figure 7-16. Baseline Operating Region
Volts
Advanced HART Diagnostic Suite
Resolutions
Figure 7-16.
4 mA
Output Current
Advanced HART Diagnostic Suite
Action
Process has very low noise. Turn off insufficient variability check
(Verification Criteria screen). Process Intelligence or Plugged
Impulse Line diagnostic will be unable to detect a significant
decrease in noise level.
Process is unstable. Increase learning sensitivity checks
(Verification Criteria screen). If this does not correct the issue,
increase the learning verification period to match or exceed the
cycle time of the instability of the process. If maximum time
does not correct the problem, process is not a candidate for
Process Intelligence or Plugged Impulse Line diagnostic. Correct
stability issue or turn off diagnostic.
With the condition present, but the process operating, go to the
SPM Status or Operational Values screen and note the current
statistical values and compare to the baseline and threshold
values. Adjust the sensitivity threshold values until a trip of the
diagnostic occurs.
The most likely cause is a fast change in the value of the process
variable. Direction of the change is not important. Increase the
learning/monitoring period to better filter out increases in
standard deviation.
20 mA
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