I don't have a 3051S, nor have I configured one, but I was curious about plugged line detection when a Linkedin group for plugged process lines appeared. I watched a couple plugged impulse line YouTube videos, but they were merely marketing hype intended to convince me that plugged lines are problem, (duh . . .), so I perused the Rosemount 3051S manual.
Here's my understanding from looking at the manual:
Plugged impulse line detection is part of the ASP (Abnormal Situation Prevention) Diagnostics Suite, an option on the 3051S (retrofittable in the field if not already on the unit). Part of the ASP diagnostics is SPM, Statistical Process Monitoring. This feature is accessed and configured with the appropriate EDDL file in a HART master.
SPM looks at the process noise (most transmitters use floating point internally with values out to the 6th or 7th decimal place) and 'learns' a baseline of statistical process noise.
In the case of plugged impulse lines, the user then assigns a low deviation threshold (alarm) values below the mean process noise value for alert or alarm actions.
A mild deviation triggers an alert, which appears on the local transmitter LCD display or a host that handles HART alerts.
A significant deviation can trigger an 'alarm' status that drives the primary 4-20mA output to a failsafe alarm level.
You said that you don't want the Multivariable, does that mean you don't care about the flow rate value? Even if you don't 'want' it, you could use monitor the signal for just its failsafe alarm condition, 22.5mA or 3.65mA whatever Rosemount uses for its failsafe output condition, and trigger failsafe as a low deviation alarm event.
Be aware that there is user effort involved in the learning process and establishing deviation thresholds, all through HART.
It appears that the raw statistical values are available via HART. Either the secondary or tertiary HART variables are can be assigned SPM statistical values. The HART variables can be read by either a HART master (Emerson AMS software or HART handheld), or by a breakout box, like the Rosemount Triloop 333 or Moore Industries HIM.
It appears to me that when a HART master like a breakout box provides the raw statistical values, then the PLC or PAC must make the alert or alarm decisions, because what I could not find confirmation of was whether diagnostic events are available as binary HART variables, either OFF or ON. That would be the best situation because then the full power of the statistical analysis is done by the transmitter, not by the user. There is a "low deviation detected' event, but it isn't at all clear whether that event can be binary HART variable, useable as a "plugged impulse line" alert or alarm. Ideally one would want to monitor the HART secondary variable for a logic 1 as an alert, with a logic zero as normal conditions, but I just couldn't make the leap to that.
quote from manual:
Detection
If the SPM diagnostic detects a Standard Deviation or Mean change outside the threshold values, one of the indicators in the SPM Status box will illuminate red, indicating if there has been a mean change, an increase in noise or variability (High Variation Detected) or a decrease (Low Variation Detected), the transmitter will take the action as determined by the user in the configuration. The LCD will also indicate the diagnostic condition. The “Time Since Detection” clock in the Time box will start incrementing. The diagnostic condition is latched and the “Time Since Detection” clock will continue to increment until the diagnostic is reset or turned off. end quote.
There's local indication of detection, but the 'actions as determined by the user in the configuration" are not listed in the manual.
If your PLC AI's are HART compatible, then they can like read the secondary or tertiary HART value directly. If the PLC AI's are not HART compatible then you need a breakout box to read the raw statistical values.
Rosemount's breakout box is the Triloop 333 which converts HART variable to 4-20mA analog signals. I've read references that infer that its programming is still DOS based. I'm not sure, but before I bought one, I'd check into how it gets configured and with what software. At one time, Rosemount would configure it for the correct variables, but I don't know if they still do.
An alternative break-out box is the Moore Products HIM module, which does the same thing and its programming is not DOS based.
The Section 7, Advanced HART Diagnostics section of the 3051S manual has about 20 pages on the topic. Worth reviewing if you're even thinking of doing it.
