New Profibus Technology Makes Field Device Replacement Easier

Related Vendors

Elementar Analysensysteme GmbH

CAC ENGINEERING GMBH

Anton Paar GmbH

PROFIBUS Nutzerorganisation e.V. (PNO)

No Confusion Caused by Diagnostics

Profibus devices provide the user with a multitude of diagnostics. Both process-specific and device-specific diagnostics are available. Thus, an electrical system fault would represent a device fault, while exceeding the maximum fill level would represent a process anomaly. Modern field devices offer a wealth of different diagnostic messages, many of which are not necessarily of interest to plant operators but instead are intended for maintenance personnel.

PA Profile Version 3.02 has introduced a solution for this: namely, classification of diagnostic messages according to NAMUR Recommendation NE 107. In this approach, the status that is output to operators is limited to four categories: “failure”, “function check”, “out of specification”, and “maintenance required”. The objective is to lessen the burden on the plant operator by providing only the information that is necessary for reliable process operation.

In addition, maintenance personnel always have access to detailed diagnostic information so that appropriate actions can be taken. Evaluation of the status information in the process control system requires a corresponding function block that is used to logically combine the bit information of the status byte with the proper status symbol. Although this function block is not a standard feature in every control system, it can be easily created with little effort.

Good Prospects for Performance Without Problems

Early tests involving the first field devices to be developed according to PA Profile Version 3.02 show that manufacturers have consistently met the requirements. Besides testing the implementation of NE107, device replacement was intensively tested and checked using control systems of different manufacturers. The good news here is that no problems were encountered with device replacement with any of the control systems.

But what’s the situation in the real world? Since adoption of the specification at the end of 2009/beginning of 2010, the number of field devices developed according to the new PA Profile Version 3.02 has risen steadily. At present, more than a dozen field devices of different manufacturers are available that conform to the profile as defined by PI.

How these devices perform in the real world will be revealed over the next few years. As the past has shown, however, users can be certain that specified devices will function problem-free, even when combined with devices developed by different manufacturers or according to different profile versions in the same plant.

The functions of the PA Profile Version 3.02 provide users with powerful possibilities for operating plants more efficiently: Device replacement — whether planned or unplanned — is significantly easier now. The main advantages are the significantly faster replacement time and the reduction in stock on hand, which in turn not only reduces costs but also increases plant availability. In addition, by grouping diagnostics into four categories, transparency at the human-machine interface is created. Every diagnostic message can be quickly intercepted and appropriate measures taken.

* The author is Head of PI (PROFIBUS & PROFINET International) Working Group “Marketing Process Automation” and Fieldbus Marketing Manager, Endress+Hauser Process Solutions AG, Reinach/Switzerland.

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