Fieldbus: Commissioning with Advanced Diagnostic Tools
Process plants with fieldbus
Modern day field devices can transmit additional status information such as the break-away and run time of valves or other status referring to device usage. Predictive maintenance is performed based on the actual status of the field device versus time-based at regular intervals. DCS manufacturers respond with comprehensive asset management systems. They facilitate need-based maintenance activities sometimes doubling time intervals compared to standard procedures.
Additionally, remote configuration via the fieldbus speeds up change over activities i.e. in batch processes or when a field device is exchanged during plant operation. With all these and more benefits gained, fieldbus has proven its value even in the conservative segment of plant process automation.
Advanced diagnostics demystifies fieldbus communication
The Advanced Diagnostic Module monitors the fieldbus physical layer during operation.
Modern day fieldbus diagnostic tools – such as the Advanced Diagnostic Module for the FieldConnex® Power Hub – bring transparency to the fieldbus physical layer and communication. The module performs measurements such as supply voltage, load current, signal level, line noise or jitter. The module listens to the communication and distinguishes between segment and device information. Clear and concise displays within the Diagnostic Manager show readouts to the user – this brings transparency to a plant condition that seems ambiguous.
- An existing cable was used with improper capacitive and inductive values
- An improperly closed housing may allow water ingress. Corrosion will cause the signal transmitted by the field device to slowly decay
- Connections may degrade due to vibrations
- Cable or field device components deteriorate over time
- Wire strands from the shield may cause bad isolation between the two poles or against ground
- Improperly chosen grounding and shielding techniques may cause loops that enable induction of noise
The compound of multiple cases often causes situations leading to the above user descriptions. Each individual condition may push some values of the physical layer out of specification; but it would not be enough to actually disrupt communication. Fieldbus is just that robust. However, several factors may already be pushing the limit so that one additional disturbance – such as that one frequency converter starting an induction motor close by the fieldbus trunk may be just enough to push this segment beyond its level of resistance. As a result, communication is at least temporarily disturbed.
The fieldbus physical layer is no mystery; it requires clear indication provided by the right tools such as the Advanced Diagnostic Module. All of the above conditions can easily be detected and taken care of at a convenient point in time. During commissioning, the quality of the installation will be better thus granting communications a higher level of fault tolerance. And that is not enough: Users want forewarning about disturbances before they can become critical to the process.
Warnings and alarms for proactive intervention
Communications: The signal is modulated onto the supply voltage. Bits are transmitted as rising or falling edges with 1 V peak-to-peak. This makes fieldbus communication very stable and resistive to disturbances.
Production optimized—put your mind at peace
A finely tuned and proactively maintained fieldbus system and field devices will not only increase the overall system availability and product quality. It also puts plant managers, operators and maintenance crews at ease – with the knowledge that the fieldbus installation formerly perceived as the black hole is now brightly lit and monitored by the FieldConnex® Advanced Diagnostic Module from Pepperl+Fuchs.