FF Segment Checkout and Commissioning

[jmcamposano]

What is the proper way in measuring the resistance and capacitance of the segment? Do i need to remove all the field instruments connected? or i can keep it connected in the segment? What is the best way to commission the FF instruments, doing it one by one or the whole segment at the same time? Thanks a lot.

[rezabejd]

Technical guides here (http://www.fieldbus.org/index.php?option=com_content&task=view&id=150&Itemid=326) have some recommended procedures.

Not sure how exactly to measure capacitance. We never did anything like that. I would hook up devices and see if the segment works. If there are errors, start looking.

"Too high capacitance" would manifest as highly attenuated signal / excesssive "rounding" of the sqaure wave. Relcom and P+F have some testers that will give you go / no go indications of segment health and some more detailed diagnostic information.

[chriss]

To measure the quality of your physical layer I would recommend you to have all field devices connected and then use the commissioning wizard which is a tool of the Fieldbus Diagnostic Manager. With this tool you generate a snapshot of your Segment including mean values of voltage, noise, jitter, unbalance and the like. The wizard also gives you an indication if these values are good or bad and proposes warning limits to be set for constant monitoring.
The voltage gives you an indication on the resistance of your trunk and high capacitances can result in various ways- signal attenuation, jitter, noise. You can see the capacitance in the oscilloscope as rezabejd described. As an example I attached two pictures, one a clear shot of the trunk and the other with an additional capacitance.