HI,

CAN YOU GIVE SOME IDEA WHAT TOOLS OR INSTRUMENT TO USE WHEN TROUBLESHOOTING SPECIALLY TO ALL FOUNDATION FIELDBUS INSTRUMENT AND HOW TO USE THE HART 375 FOR TROUBLESHOOTING? AND HOW TO USE A MEGGER AND TK3 BENTLEY NEVADA?

THANK YOU

 

Hi aalbin,

If your intent to learn how to troubleshoot Foundation Fieldbus problem, following link is a good start point :

http://www.relcominc.com/pdf/501-380 fieldbus physical layer troubleshooting guide.pdf

Hope this help

Regards
Aan

 

General purpose test tools and specialized fieldbus test tools can be used for troubleshooting FOUNDATION fieldbus.

It may be a good idea for the instrument workshop to have a laptop with fieldbus USB interface also able to provide power to a device, or have a handheld field communicator and separate fieldbus power supply and terminators. This allows separate testing of field devices.

*System Diagnostics Software*
The most powerful fieldbus troubleshooting tool is the DCS itself. Make sure to use a DCS where the H1 fieldbus interface card collects communication statistics and logs events associated with the fieldbus itself. The DCS should have diagnostics software that display:

. "Live list" for any port
. Event logs
. Communication statistics for each port
. Communication statistics for each device on the bus

A novice can use the system diagnostics software and make a screen capture at site and email the file to an expert in a different location for analysis.

*Live List*
The live list display lists all devices actively communicating on the bus together with pertinent information:

. Device Tag
. State (commissioned, standby, decommissioned, offline )
. Device ID (unique identifier)
. Device Address
. Manufacturer
. Type (model number)
. Device Revision
. Class (basic or link master)

This is often a good starting point for troubleshooting. If one device does not appear in the live list (but other devices appear), it means the system is not even able to detect the device in the first place. There could be a number of reasons including; device not connected (to this port), device not powered, device failure etc. If a device is intermittently appearing and disappearing it could be a problem with communication settings (although this is a rare problem since the introduction of the communication profile). If no devices at all appear

*Communication Statistics*
Communication statistics is a useful tool to capture communication errors anywhere on the bus including trunk, spur, or in the device etc. it is a very convenient tool as it can be done from the control room, without having to go into the field.

*Fieldbus Tester (e.g. MTL/Relcom FBT-6)*
A fieldbus tester is a portable test tool much like a digital multi-meter but easier to use because it is designed specifically for use with FOUNDATION fieldbus. Because the fieldbus tester is portable, it can be used to check the bus in any place along the wires including in the marshalling cabinet, field junction box, and at each field device. The fieldbus tester is ideal when laptops are not allowed in the field. The fieldbus tester measures:

. Supply voltage
. Signal level
. Noise level
. Signal wire shorted to shield
. Etc.

A novice can use the fieldbus tester to capture test data at site, transfer it to a computer, and email the file to an expert in a different location for analysis.

Document on which bus and where on the bus (at fieldbus power supply, field junction box trunk, or at device) on the bus each dataset was taken.

*Handheld Field Communicator (e.g. Emerson 375/475)*
The fieldbus handheld field communicator is the same as for 4-20 mA/HART devices. Although primarily a tool for device setup/configuration, tagging, calibration, and device diagnostics, it also includes a number of functions for troubleshooting the bus itself. The handheld field communicator includes some functions from DCS diagnostics software such as the "live list" as well as some functions from fieldbus testers such as power supply, signal level, and noise level.

Ideal where laptops may not be allowed in the field
Document on which bus and where on the bus (at fieldbus power supply, field junction box trunk, or at device) on the bus each dataset was taken.

*Fieldbus USB Interface*
Similar a USB interface for 4-20 mA/HART devices

The interface on its own doesn't do anything. It is used with software such as a bus analyzer or configuration software.

*Bus Analyzer Software*
There is no need to use analyzer software because FOUNDATION fieldbus does not have issues with different baud-rate, parity, stop bits, data types, scaling, and big-endian/small-endian floats etc. In the early days of fieldbus, interoperability was a common problem. The bus analyzer (aka bus monitor or sniffer) was an important tool to troubleshoot interoperability issues. Problems in T1/T2/T3 timers, Slot Time (ST), Maximum Response Delay (MRD), Minimum Inter-PDU Delay (MID), and Virtual Communication Relationship (VCR) etc. could be identified by experts. However, "communication profile" and ITK has overcome these issues. Therefore a bus analyzer is not needed in the field much these days (it is an important tool in interoperability test labs).

The bus analyzer software is usually loaded on a laptop and requires a PCMCIA or USB interface for fieldbus which is connected to the bus. Laptops may not be allowed in hazardous areas.

A novice can use the bus analyzer software to capture communication (record messages to file) at site and email the file to an expert in a different location for analysis.

*Digital Multi Meter (DMM)*
It is often said that it is not possible to troubleshoot fieldbus with a regular multimeter. However, a regular Digital Multi Meter (DMM), same as for 4-20 mA and on/off signals, is also a powerful troubleshooting tool for fieldbus because most problems are installation related and manifest themselves as insufficient power supply voltage at the device due to corroded terminals etc. The DMM is also ideal for checking for ground potential differences and checking for wire shorts and open circuits.

A DMM cannot be used to measure fieldbus signal level or noise level

*Clamp Meter*
A regular AC current clamp meter, same as for 4-20 mA/HART signals, is also a powerful troubleshooting tool for fieldbus because most problems are installation related including creation of ground loops due to multiple deliberate or inadvertent ground connections causing current flow in the shield/drain wire.

There should be no current flowing in the shield/drain wire.

*Portable Digital Storage Oscilloscope (DSO)*
A regular portable Digital Storage Oscilloscope (DSO), same as for 4-20 mA/HART signals, can also be used for fieldbus because most problems are installation related including running the fieldbus cable in parallel with noisy power cables in the same cable tray (a bad practice).

A novice can use the oscilloscope to capture waveforms at site, transfer it to a computer, and email the file to an expert in a different location for analysis.

Use HOLD button to capture before saving<pre>
Adjustment Setting
Coupling AC
Time scale 20 us/div
Amplitude scale 200 mV/div
Trigger Rising edge
Trigger level 50 mV
Numeric measurement Peek-to-peek
(if available)</pre>
These settings are ideal for capturing the fieldbus signal itself. If noise is suspected on the bus, various combinations of settings have to be tested to capture the noise in other frequency bands. General proficiency in oscilloscopes is then required

Note: A general purpose oscilloscope typically has a bandwidth of 20 MHz or more as well as various trigger levels and mode and may therefore be able to detect high frequency harmonics and other noise which may not be seen using a specialized fieldbus signal oscilloscope in a bus diagnostics module. However, from a general purpose oscilloscope it is not possible to tell which device's signal is displayed at any one time. One the other hand, a specialized fieldbus signal oscilloscope can selectively pick the signal waveform from any chosen device.

*Bus Diagnostic Module and Software*
A bus diagnostics module can be plugged into fieldbus power supply backplane (temporarily or permanently) and networked to a workstation for the software, or be portable together with a laptop. A bus diagnostics module can be plugged into fieldbus power supply backplane only measures in the power supply end. A portable bus diagnostics module can be used to check the bus in any place along the wires including in the marshaling cabinet, field junction box, and at each field device. The diagnostics module is the data acquisition probe, and the software takes care of display and reporting.

A novice can use the bus diagnostics module and software to capture test data at site and email the file to an expert in a different location for analysis.

Note: A specialized fieldbus signal oscilloscope in a bus diagnostics module has fixed trigger mode and levels and options and may therefore not be able to detect high frequency harmonics and other noise which may be seen using a general purpose oscilloscope with a bandwidth of 20 MHz or more. A specialized fieldbus signal oscilloscope can selectively pick the signal waveform from any chosen device, while with a general purpose oscilloscope it is not possible to tell which device's signal is displayed at any one time.