Are you fully plugged in to plugged impulse line problems?

Les Slocombe, product marketing manager – Sensing Solutions, ABB Limited, explains how developments in pressure transmitter technology are helping to simplify the long standing challenge of identifying plugged impulse lines and minimise the amount of time needed to trace and solve plugged impulse line problems.

When it comes to pressure measurement, the efficiency of any process relies on having the most accurate information possible, hence the importance of being able to detect errors as soon as they occur. However, with pressure transmitters rarely directly connected to the processes being measured, the problem of blocked impulse lines is common.

Transmitting the pressure signal from the process to the transmitter, these small diameter lines are prone to plugging caused by freezing or products solidifying in the line. With no direct impact on the transmitter itself, the problem is often difficult to trace, as the measurements continue to look plausible.

Developments in both signal processing and operator interface technology are enabling plant operators to move from a preventive maintenance setup to a proactive maintenance routine based on enhanced device data.

New technology solves a forgotten problem

To help tackle the problems caused by plugged impulse lines, some manufacturers, ABB included, have developed technology to help operators more easily identify the existence, and scale, of plugged impulse lines – using the background noise of the process. This technology uses an algorithm to compare the current performance of a pressure device against a background ‘template’ set during commissioning.

The blocking of one impulse line leads to the pressure fluctuations not being cancelled anymore, resulting in the process noise being included in the differential pressure signal. When both impulse lines are plugged, the noise level of the sensed differential pressure is almost reduced to zero.

The major cost-saving benefit of plugged impulse line detection arises from the reduction in preventive maintenance. The plugged impulse line detection data from the pressure transmitter should be available from the maintenance workplace and in the control room. With fieldbus and asset monitoring, it should also be possible to access the PILD data, and a range of other device data, from a single location.

Detection in the field

With the current challenges surrounding deskilling and reduced maintenance resources, it really is important for engineers to be able to quickly and easily trace and rectify a fault wherever possible.

While most industrial pressure transmitter manufacturers have developed ways for maintenance engineers to locally interact with devices, until now, most have either used proprietary systems or require specialist operator knowledge. Furthermore, the inclusion of plugged impulse line detection functionality has tended to be limited to higher end transmitter models, requiring plant operators to pay more if they want to have it included.

The latest generation of ABB 2600T pressure transmitters features plugged impulse line detection functionality as standard. For ease of operation, many of the basic detection and diagnostic functionality is accessible via the local HMI. Those functions that cannot be handled via this interface can be accessed via ABB’s PC-based AssetVision software, which can be run on a laptop plugged into the transmitter.

The software enables operators to perform a simple five stage process which assesses background noise, tests the PILD condition and enables adjustment of parameters. It can also be used to ‘train’ the transmitter, enabling the background noise algorithm to self-adapt to the specific process conditions at the time of installation. Using this information, it is then able to detect variations in process conditions that indicate a plugged impulse line.

Summary

The ongoing drive towards low-cost plant operation will increasingly favour instruments that help operators ensure minimum downtime and cost caused by unforeseen maintenance.

With new technology opening up a raft of new options, including the ability to quickly trace and rectify plugged impulse lines, now is the time for plant operators to ask whether their existing pressure transmitters are really up to the job.

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