Accelerated Commissioning – Diagnostic module facilitates handling fieldbus and generates new service offerings

The Advanced Diagnostic Module by Pepperl+Fuchs accelerates the commissioning of fieldbus systems, faults are detected earlier, and the system availability is increased due to predictive maintenance. Automatically generated documentation creates a clear situation for the handing-over of the system – both for the commissioning company and for the customer. The fields of application of the supplier-independent, mobile version of the efficient diagnostic tool might inspire many a service provider to offer various services which up until now, were absolutely unfeasible.

A good installation is the best basis of reliable digital communication. This is the conclusion of the BIS Prozesstechnik GmbH test laboratory during the current examinations on trouble-shooting at the physical layer of fieldbus systems. Therefore, it is important that existing faults are detected during the commissioning but, how can you ensure this and how can you guarantee the best possible design of the physical layer of a fieldbus of the individual segments? For this purpose, the use of state-of-the-art diagnostic tools as offered by Pepperl+Fuchs are recommended. The Advanced Diagnostic Module (ADM) toolsuite examines the physical layer of the fieldbus during the installation and warns against faults before a device fails during operation.

The Advanced Diagnostic Module by Pepperl+Fuchs combines all functions for fast and efficient detection of usual causes of faults. The module does not only detect interfering signal levels but also insufficient signal levels, wrong device polarity or grounding faults. Wrong wiring, short circuit or excessive resistance do not pose any problems for this clever tool. The commissioning personnel are immediately informed by a corresponding indication should any difficulties occur during the commissioning. In this way, the faults can be restricted with the software, and the problem can be eliminated.

Following the definition of tags, the Advanced Diagnostic Module will display an overview with practical information on voltage, symmetry, noise, jitter and min. or max. signal levels of the respective segment. Subsequently, the software calculates individual warning values for each single field device and is designed such that continuous operation of the segment will always be ensured. After the measurement, a complete protocol including all min./max. values will be generated automatically – for the system and for each connected field device. In this way, fieldbus signals can be completely evidenced and documented.

Transparenz par excellence

The documentation creates a clear situation for the handing-over, both for the commissioning party, i. e. contractor, system integrator, technical service provider or the manufacturer of the process control system, and for the end user. Problems occurring later can be easily compared with the result during the handover, and a reasonable cause analysis can be carried out. For service providers, this reduces warranty costs and consequential damages. Commissioning costs are reduced by the higher degree of automation because measurement values do not have to be recorded manually anymore which used to be a time-consuming process.

Moreover, with the ADM, the actual power reserve of each fieldbus segment can be precisely determined during commissioning. From this, you can deduct the user's margin left within the specification. For every field device and segment, the actual load and the signal strength can be measured directly at the clamps of the power supply.

Experience has shown that every process plant will be retrofitted many times during its life cycle, or will be expanded by some measuring points and as a matter of course, the operating company will carry out maintenance work at times. Every modification can have a lasting effect on the physical layer of the fieldbus and so the module turns out to be very useful. The diagnostic module now allows the measurement of the current operating states in regular intervals. The software detects deviations which in the long term could result in a fault, it automatically transmits a warning message and renders proactive trouble-shooting support.

The Jitter as Quality Factor no. 1

In principle, three parameters – jitter, signal level, and noise – can be used as quality factors for fieldbus networks because their limit values are clearly defined in the fieldbus standard IEC 61158-2. However, the examinations carried out by the BIS Prozesstechnik GmbH test laboratory showed that the jitter is particularly suited for monitoring of the physical layer of the fieldbus. The jitter measurement is extremely complex, and the developers at Pepperl+Fuchs have mastered this challenge.

The edge of an ideal fieldbus signal describing the logic state of a bit theoretically comes exactly in the middle of the bit time. The point in time at which the signal edge passes the supply voltage level is called zero crossing. In practice, the existing inductances and capacitances of the connected devices and of the power supply system, the cables and the connection system influence the signal. Moreover, the topology, i. e. cable length and number and distribution of the field devices plays a role. Therefore, it is inevitable that the zero crossing in real systems varies and this is called jitter. Important fact is: If its values becomes excessive, the signal edge will leave the measuring window in which the receiver measures the polarity of the edge, and a bit will get lost. Algorithms ensuring data transmission will detect this fact and will reject the telegram as defective. There will be repetitions, if required, and the complete communication process may even stop. The process control system will record occurring telegram repetitions, but it is not able to check the signal quality of the individual parameters.

The diagnosis of the physical layer and the ability to measure jitter enables clear attribution to possible causes of faults, such as a creeping change in the capacitance of the terminators or corroded clamps. Some problems require the user to carry out a more profound examination of the problem. In some cases, only the integrated oscilloscope may be able to give information on a defective field device.

The Jitter as Quality Factor no. 1

For the specific requirements of different target groups, Pepperl+Fuchs offers the Advanced Diagnostic Module in two designs. There is a stationary and a mobile version. The stationary version is intended for users who wish to control the physical layer of their fieldbus segments. It plugs into a free slot of the power supply system and it is able to monitor up to four segments simultaneously:

• It is used to verify the physical layer of the fieldbus during commissioning
• With warnings and alarms, it informs about abnormal changes of the physical layer – incl. creeping changes
• It can be used for troubleshooting in case of complex faults
• It also allows external access, e. g. via Internet

If a Pepperl+Fuchs power supply system isn't used, at least the mobile version of the ADM can be used. With the exception of some points, it has the same functionality as the stationary module.

At any rate, diagnostic modules open up completely new service concepts. For example, in future a service provider could offer his customers the option to carry out a complete measurement of the physical layer of the plants. Inspections in regular intervals could minimize unscheduled plant shut-down. The report on the state of the fieldbus systems in regular intervals creates confidence in the technology. Service 24/7 for acute problems is imaginable. A remote maintenance via Internet for users who decided in favour of continuous online diagnosis of the physical layer could extremely facilitate the repair work - a service which also could be offered on a worldwide basis.

The ADM by Pepperl+Fuchs, fist of all, saves plenty of time during commissioning; secondly, creates a quick remedy in case of problems; thirdly, minimizes cost-intensive, unscheduled plant shut-down periods and, fourthly, considerably increases the system availability. For service providers, it is possible to accelerate the commissioning and to hand over the system on schedule. Moreover, with the mobile diagnostic tools companies could offer many new after-sales services including maintenance and repair and open up an additional market potential for themselves.