troubleshooting lontalk wiring sec i, ii, iii, iv.updted

Troubleshooting LonTalk communications wiring with LonTalk protocol analyzer, LonTalk switch, recording resistance meter, and Rover.

Tech support has a kit with the equipment discussed here. It is available for loan. Contact Tech support in St. Paul for information. Topics covered: I) a general overview of LonTalk communications problems. II) Getting started with LonTalk switch and LonTalk protocol analyzer to diagnose LonTalk wiring problems. III) Using resistance measurements and recording multi-meter to diagnose LonTalk wiring problems. IV) An example of a systematic approach to dividing the link.

Part I: Overview:

The main points:1) Some kinds of communication failures can be fixed from the Summit workstation, for

example PEAK database errors or errors that occur during Neuron ID (NID) assignment. However, many if not most, communications problems are caused by wiring. In particular proper wiring and crimp connections are very important, as is proper termination. Mixed wire types is very bad. In some units communications can be terminated at a low voltage termination board. The wire connecting the controller to the low voltage board may be different than for the rest of the link. This should be ok if this is wired as a stub. (Or connect the comm. link directly to the controller.) Improper shielding is bad.

2) Divide the link to isolate problems.3) Be systematic. Document. There is no magic wand.4) Override equipment. Use Summit log and trends, protocol analyzer, and recording multi-

meter and Rover to collect data more efficiently and over extended periods of time. 6) Associate the occurrence of problems with events at the site.

Some LonTalk communications failures are caused by software problems. If Rover can discover the link it may be that the cause is in the BCU or Summit. These problems take less leg work to fix and are generally much easier and less time consuming. It is always worth exploring this possibility. However, LonTalk communications failures are very often (maybe most often) caused by physical problems with the communications wire, its topology, its termination, or connections. This discussion is about finding failures due to problems with the wire. It is difficult and time consuming to find and correct these problems because the link may be many thousand feet long. Access is difficult. Its route through the building and its topology may not even be known.

Even though comm. loss diagnostics in Summit often define the existence of a problem to the user, in reality neither Summit nor the BCU are very sensitive to problems on the communication link. Missed or corrupted messages are re-sent many times before a failure is reported by Summit. Redundancy that is designed into the system makes it very tolerant. Equipment is designed to operate well stand-alone so in most cases the temporary loss of communications is not catastrophic to overall system function, and in many cases may not even be noticed. The LonTalk protocol and hardware itself is very robust. This means that underlying problems may

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be present yet remain undetected for long periods, or may be only occasionally detected. When symptoms are seen they often seem to be phantoms, first comm. is lost to one device, then another, then to many, then not at all. When the problem is intermittent it may be necessary to invest considerable time simply observing the site in order to see any symptoms at all. This time is certainly expensive, may be hard to justify to a user, and is often frustrating.

The basic method for finding and correcting these problems is to divide the link and then to see which of the individual segments continue to show symptoms. Unfortunately there is no silver bullet solution to this problem, but there are a few methods and tools that can help. The most important might be recognition that shortcuts may end up wasting time. Patience and a dogged, systematic approach are very important. More sensitive tools that can collect information unattended for long periods like a LonTalk protocol analyzer can be very helpful. Any method that leaves the link intact is preferred since leaving parts of the link disconnected for long periods will, at the very least, generate a conspicuous number of comm. loss entries in the event log. Dividing the link can help determine where problems may be occurring but not the cause. Common problems are crushed or broken wire, shorts, opens, loose connections, loose or poorly crimped spade connectors, missing, loose (or extra or incorrect) termination resistors. Check for this kind of thing everywhere you go, you just may get lucky.

It might be possible to associate the occurrence of symptoms with events in the building like changes in occupancy, equipment starts/stops, or specific activities like cleaning or lunch. Or, who knows what else. This may suggest locations where problems may be present or possibly a cause. Sometimes the operation of a particular piece of equipment may be associated with a problem. If this is the case overriding equipment on or off may be informative. Trends set up in Summit when compared to LonScanner logs, resistance measurements, or other information may be helpful with this.

It may be useful to start out by compiling some basic information about the link. A map is a good idea. Transactions in the LonScanner log are identified by Domain Subnet Node (DSN) address or NID so a list of all the controllers that contains location label, NID, DSN, and position in the link is a good place to start. Resistance is one of the best indicators of wiring problems. Check and record resistance on individual segments of the link every chance you get. Keep in mind that the resistance may be abnormal only during periods when problems are actually occurring so during the, possibly long, periods when there are no communications failures and no corrupted messages (i.e. Cyclic Redundancy Check (CRC) errors), it may be just fine. A meter that records resistance over time, or records minimum and maximum, can be very useful because it will collect information unattended. It may then be possible to relate unusual resistance measurements to events in the building, Comm. loss diagnostics in Summit, Summit Trends, the Summit Event Log, and Logs from a protocol analyzer.

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Part II: Using LonScanner protocol analyzer or Rover, and Loytec L-switch LS-33CB for diagnosing LonTalk communications problems.

The main points: 1) The protocol analyzer is a very sensitive tool to diagnose LonTalk communications and it

can be left on site to monitor the link for extended periods. It can detect CRC errors.2) CRC errors are also recorded by individual controllers. Rover can get this information. 3) CRC errors are often caused by wiring problems. Segments with CRC errors probably

have at least one wiring issue like a short or a bad crimp connection.4) The Loytec switch can divide the link without further disrupting communications. It does

not pass CRC error messages so bad segments of the link can be isolated and detected with the protocol analyzer.

A LonTalk protocol analyzer like LonScanner reads and records every message on the link. The LonScanner log will thus contain a more complete list of suspect events than the Summit Event Log because Summit is very tolerant of missed messages. It may then be easier to associate events in the LonScanner log with conditions in the building (such as occupancy or equipment starts and stops) when all suspect events can be identified rather than the few that make it into the Summit Event Log. No one needs to be present, saving time. When it is connected it can be left alone to collect information continuously for the hours or days that may be necessary to detect an intermittent problem. This is a two edged sword. On the one hand it can detect events that are symptomatic of underlying problems but are not extreme enough to cause a Summit diagnostic. It can therefore detect problems in less time than simply looking at the Summit event log. On the other hand it generates a blizzard of information that is difficult to sort through. There may be dozens or possibly hundreds of messages per second with millions of log entries over a 24 hour period. If troublesome episodes of comm. loss are intermittent and separated by hours or days, the log file will be very large with relatively few interesting entries buried in it.

Of particular interest are messages that are corrupted, or CRC (Cyclic Redundancy Check) errors. In practice these are almost always caused by wiring problems. A few CRC errors are normal but a link that is functioning well may have no more than one CRC over thousands or tens of thousands of messages. More than this is indicative of a problem. Some problem sites may go hours, days or even weeks with only a handful of CRC errors separated by periods of seconds or minutes or hours where 10%, 50%, or more of the messages are bad. It may seem surprising that during some of these extreme episodes the Summit Event Log may show few or no comm. loss messages. This illustrates both the power of the protocol analyzer and also how robust the Summit system really is.

Individual LonTalk devices also record various kinds of communications packet errors. For Trane controllers this information is available with the Rover service tool. Connect with Rover; select Device/Troubleshoot/Test. CRC errors are labeled Transmission errors. Reset sets errors to zero. Comparing this statistic between controllers on different isolated segments of the link may be informative. A protocol analyzer provides more information but using Rover in this way allows CRC errors to be recorded on more than one segment at a time.

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Physically dividing the link can be accomplished in a number of ways. Of course the simplest is to just disconnect part of the link, add new termination resistors as appropriate, and troubleshoot each of the parts independently. It is possible to look at resistance values on different segments in this way but communications is lost entirely to all but the segment that contains the BCU. This is generally not a good thing for long periods of time. A Trane repeater can be used to physically divide the link for diagnostic purposes while still allowing communication to both parts of the link. However it passes all signals from one segment to the other regardless of whether the sending and receiving devices are on the same or different segments. Corrupted messages (CRC errors) are also passed from one segment to the other so it is not possible to determine the segment where CRC errors originate. A LonTalk switch such as the Loytec L-Switch also physically separates the link into two segments. When configured in the switch mode, it learns which devices are on which segment of the link, and it passes messages from one segment to the other only if the sending and receiving devices are on different segments. Corrupted messages on one segment are not passed across the switch. When used with a LonTalk protocol analyzer it is now possible to identify segments of the link that are the source of CRC errors. These are segments that contain suspected wiring problems. Keep in mind that there may be multiple problems on different segments of the link. With the Loytec switch the whole communications link can remain in service while information is being collected.

Getting Started with LonScanner: LonScanner is protocol analyzer software from Echelon. It can be purchased for about $400. It uses the same Echelon USB hardware connection as Rover. For complete information about LonScanner refer to The Users Guide for LonScanner. It can be found on the laptop kit hard drive at: C\LonWorks\LonScanner.

Connect the Echelon LonTalk USB adapter to the link just as you would for Rover Comm. 5. LonScanner needs to know the name of the interface. On the tech support laptop the USB adapter is LON3. This can be confirmed by opening LonWorks Interfaces in the Control Panel and selecting the USB tab. Test the hardware by selecting the Test button. In the Test window select Comm. Press the service pin on a device on the network. If the service pin message is acknowledged (ping passed) the hardware is working.

Open LonScanner through Windows Start Button. Select the interface name from the pull-down (LON3 probably). Select the radio button for: Monitor a LonWorks Network Interface (or select: Open an Existing Packet Log to view a saved log). Select the +/- Capture button to begin capturing packets. LonScanner will start capturing every message on the link. The amount of information can be overwhelming. Each message has an identifying number and a time stamp. All the information in the packet is recorded including the sending device, the destination, type of message, message attributes, and all the data. The data is hard to decipher. Network variables are identified by selector number or NV index, not by name, or even type. All the information is in hex. The source and destination are identified by subnet and node. The BCU is easy to identify, it will be the only device on subnet 255. Screen shots from Rover can be used to determine the names of devices and their DSN addresses.

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The LonScanner log file will be very big. It can be saved to the local hard drive and transferred to a USB thumb drive. LonScanner limits the size of the log. Change the log max size by selecting File/Preferences. Make sure the max size is large enough to accommodate a sufficient time period, but not so large it will not fit on the disk. Try setting it to a few GB to start.

For starters there are two things to look for. CRC errors are messages that are corrupted. These are failed communication attempts and definitely indicate a problem. Experience shows that they are usually caused by wiring problems. The second thing to look for is an “L” in the Attr column. When the BCU expects a message to be acknowledged but does not receive one, it will resend the message with the “L” attribute. A lot of “L”s in the Attr column may mean that the BCU is having a hard time getting the responses it needs and is having to repeat a lot of messages. Messages may be getting lost or corrupted, or, devices may be off line. Use a spreadsheet or some other method to record periods when there are a lot of CRCs or “L”s in the log and compare this to other records.

A third thing to look for is Bandwidth. Bandwidth should stay under 40%. Networks with higher bandwidth will start to experience problems with message collisions, another source of CRC errors. Message acknowledgement will begin to fail. Messages will need to be repeated. Some third party devices flood the link either by polling too fast, requiring acknowledged service, or by updating frequently on a very small change in value.

A fourth thing to look for is short messages. Short messages are often the result of noise.

In order to save logs select File\Save As, select the desired location in the pull-down, and give the file a descriptive name. By default, logs are saved to the LonScanner folder (C\LonWorks\LonScanner). It may be convenient to create your own folder to store the logs i.e. C\Lonworks\LonScanner\My_LonScanner _Logs.

The “Binocular” button is a find function that allows a log to be searched for CRC errors or “L” Attributes.

The log file can be printed in whole (don’t do this, it will take a long time and use a lot of paper) or in part.

Getting Started with Loytec L-switch LS-33CB: See the L-Switch Users Manual for detailed information about the L-switch. The Loytec folder on the tech support laptop has a PDF for the user manual as well as an installation guide, a copy of the Loytec Serial Update tool (LSU tool), current firmware, and a data sheet from Loytec. The Loytec website has additional resources. The L-Switch costs about $400.

The L-switch Dip switches 1, 2, and 3 should be down. Dip switches 4, 5, 6, and 7 should be up. This configures the device as a “smart switch”. Other configurations are possible but this is what we want for our purposes.

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Connect power to screw terminals 16 and 17 on the right side of the switch. It can use either 12-35VDC or 12-24VAC. The 24VAC power supply used for most Trane controllers works.

Connect the Comm. link segments to the FT 1 (screw terminals 5 and 6) and FT 2 (screw terminals 2 and 3) connections on the left side of the switch. If the wire is the 22 AWG level 4 use a 105 ohm termination resistor. If the wire is the 18 AWG Trane purple wire use an 82 ohm termination resistor. Trane recommends unshielded wire but if the wire is shielded it must be grounded at one end of the segment. It should not be grounded at both ends. In the middle it must be tied together at each node and taped. Keep in mind that there are now two separate segments. Improper termination resistors or improper handling of the shield (if present) can cause problems so be careful about this.

If configured as a smart switch, as suggested here, the L-Switch will be transparent on the network. Like the Trane repeater, the BCU and Rover will not know it is there. For its own use it keeps a list of which individual devices are on which segment. This is good because it allows the L-Switch to filter CRC errors. However, when the L-Switch is moved to a different location the list needs to be rebuilt. Hold the status button for more than 20 seconds to clear the list. The L-Switch will then rebuild its list for the new location.

Firmware is downloaded using the Loytec serial upgrade tool (referred to as the LSU tool on the Loytec website) through the nine-pin serial port. You can use the comm4/serial USB adapter that comes with Rover. Set the dip switches on the adapter for RS-232 and connect with a nine pin null modem cable. The cable that comes with Tracer SC will work. The process is detailed on page 39 of the Users manual. The LSU tool can also be used to configure the L-Switch. Keep it simple, don’t mess with this. Current versions of the LSU tool and the firmware are available on the Loytec website. Ordinarily it will not be necessary to upgrade the firmware or to use the LSU tool.

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Part III: Using resistance measurements and the Metex M-3860D recording meter to diagnose LonTalk communications wiring problems.

The main points:1) Resistance is important. It should be steady. It should not vary by more than 1 or 2

ohms. Use Ohms law to make sure that resistance of the sub-divided link is consistent with the resistance of the whole link and parent segments.

2) The exact resistance depends on the type of wire and on where the measurement is made (end or middle). See link resistance table below.

3) Poor crimp connections are a common source of problems. Get a good crimping tool. Mixed wire types is very bad. If wire is shielded make sure it is continuous and grounded in one place and one place only.

4) The minimum resistance on a properly terminated line is 52.5 ohms (22 AWG level 4 wire) or 40 ohms (18 AWG purple wire). If resistance is less than this there is an extra termination resistor, a star or branch topography, or if very low (0-10 ohms), a short between the twisted pair comm. wires.

5) If resistance is 105 ohms or higher with 22 AWG wire (or if resistance is 80 ohms or higher with16 AWG wire) there is probably an open on one side of the link, or a termination resistor is loose or missing.

6) If Rover consistently fails to discover devices beyond a certain point on the link look for a short in the comm. link between that device and the next.

7) Use Metex M-3860D or similar recording meter. Install logging software from the floppy disk that comes with the meter. Create log file. Set sampling interval. Set Hi and Lo limits. Log samples outside limits.

8) Divide the link; connect meter to different segments to isolate problems. 9) See Topics article 10-4 Nov/Dec 2001.

Why resistance is important: The value of termination resistors is carefully selected to match the characteristic impedance of the line. This is very important because it minimizes noise and signal loss and degradation. Communications difficulties can be expected unless the line is terminated correctly. Note that it is the value of the termination resistor that must match the characteristic impedance not the resistance measured on the line as a whole. Do not try to achieve a particular resistance reading by changing the termination resistors.

While there are some kinds of problems that can be fixed with software at a workstation, experience shows that LonTalk communications problems are most often caused by communications wire that is damaged, improperly terminated, or has poor crimp connections. Any of these things will affect the resistance of the link so one of the most useful methods for identifying and isolating this kind of problem is to measure the resistance on the link.

What the resistance should be: The resistance of a LonTalk link can be complicated. It depends on the type and length of wire, where on the link the measurement is taken (the end, middle, etc.), topology, and the type of termination. Trane makes this considerably simpler if our wiring recommendations are followed.

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The topology will be the simplest possible, a daisy chain with no branches or stars. See Figures 1, 2, and 3 below for some examples. The wire will be the same throughout and will be one of two types (either 18 AWG “Trane purple” or level 4 Echelon). The wire will ordinarily be unshielded eliminating the problems associated with improperly landed shield. However if shielded wire was used, make sure the shield is continuous and is grounded in one place only. If the shield is not grounded anywhere or is grounded in more than one place it may generate noise in the communications wire. Resistance should be infinite between the shield and either of the twisted pair wires. Termination will be only at the ends of the link and will be either 82 ohms (for 18 AWG “Trane Purple” wire) or 105 ohms (for Level 4 Echelon).

We usually measure resistance with the link intact. In this situation the observed resistance is the result of a simple circuit with two parallel resistances. On each side of the circuit the resistance is partly from the termination resistor (the same on both sides), and partly from wire (possibly different on each side). We know the resistance of the wire per unit length (16.2 ohms per 1000 ft for 22 AWG, or 6 ohms per 1000 feet for 18 AWG). If we knew the length of the wire we could calculate exactly what the resistance should be. Unfortunately we can usually only guess at this, so practically speaking we can only know within a fairly broad range what it should be. On the other hand, the LonTalk signal itself is small, so we can at least say that the resistance on a properly functioning LonTalk link will be nearly constant. It should probably not vary more than a few tenths and certainly not by more than 1 or 2 ohms over time. Resistance that fluctuates more than this indicates a problem. Resistance measured on segments of the link should always be consistent with the resistance of the combined parts. Use ohms law to determine if this is true.

22 AWG

18 AWG

22 AWG

18 AWG

22 AWG

18 AWG

22 AWG

18 AWG

Length (feet) end end half half quarter quarter eighth eighth0 52.5 41.0 52.5 41.0 52.5 41.0 52.5 41.0500 56.3 42.4 56.6 42.5 56.5 42.5 56.4 42.51000 59.5 43.8 60.6 44.0 60.3 43.9 60.0 43.91500 62.4 45.1 64.7 45.5 64.1 45.4 63.4 45.22000 64.9 46.2 68.7 47.0 67.7 46.8 66.6 46.62500 67.1 47.3 72.8 48.5 71.3 48.2 69.6 47.83000 69.1 48.4 76.8 50.0 74.9 49.6 72.5 49.13500 70.9 49.4 80.9 51.5 78.4 51.0 75.3 50.34000 72.5 50.3 84.9 53.0 81.8 52.3 77.9 51.54500 74.0 51.2 89.0 54.5 85.2 53.7 80.5 52.65000 75.4 52.0 93.0 56.0 88.6 55.0 83.1 53.7

Table 1: Eaton’s resistance table. Resistance of a properly terminated LonTalk link for different types of wire measured at different points along the wire. This is parallel resistance on an intact link. Note that the maximum recommended length is 4500 ft. Information for 5000 ft. is only for comparison.

Series resistances. It can also be useful to measure the resistance with the link open. If the wiring follows the Trane recommendations this is a series resistance partly from the termination resistor and partly from wire. This resistance should be at least the value of the termination

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resistor (with a daisy chain the wire can only add to this value). If it is less than that there is probably an extra termination resistor, or some other parallel resistance, somewhere along the wire. This resistance should be exactly the same measured from either end. If it is not, the link may not be a daisy chain or there may be an extra termination resistor. The link can be further subdivided. The sum of sub-segments should always be consistent with a series circuit and equal to the resistance of the whole. Use Ohms law to calculate this. This information can be used to identify parts of the link that are problematic.

Some kinds of wiring problems show characteristic resistance readings. A resistance of 105 ohms or higher (for 22 AWG wire) or 80 ohms or higher (for 16 AWG wire) indicates an open. Either the wire is broken or the second termination resistor is absent. (The measured resistance is due to a single termination resistor plus some wire). If resistance is high, but less than 105 (or 80 if 16 AWG) there may be a loose connection or corroded connectors. A very low resistance (say < 10 ohms) indicates a short between the comm. wires. This could be caused by poor connections or wire that is crushed or damaged in some other way. Resistance less than 52.5 ohms (22 AWG wire) or 40 ohms (16 AWG wire) indicates an extra parallel resistance, possibly an extra termination resistor or a non-daisy chain topology. Damaged wire, poor connections, or partial shorts or opens combined with vibration or temperature changes can produce resistance that varies. Wire that is stretched too tight may strain connections when the temperature changes causing the resistance to change. Again, subdivide the link to isolate the problem.

Use Rover to discover the link or segments of the link. If Rover consistently fails to discover devices beyond a certain point on the link look for a short between that device and the next device. In many cases the short will be intermittent so this observation may not be clear-cut. Once the link is divided it is still worthwhile to discover both sides with Rover.

Crimp connections:Poor crimp connections are a major cause of LonTalk wiring problems. Inexpensive crimping tools just crush the wire and the connector together. This can result in damaged wire, a poor connection, or over time corrosion in the connector. A proper crimp makes a cold weld between the connector and the wire. A good quality crimping tool will have special dies for different kinds of wire. There may be special connectors designed specifically to fit the tool. The tool will have a ratchet mechanism to assure that the crimp is made with the proper pressure. A tool like this may cost several hundred dollars but it is well worth the cost. Make sure wiring contractors are aware of the importance of proper crimp connections.

Metex M-3860D recording multi-meter: Communications problems are often hard to diagnose because they are intermittent. If the problem occurs only a few times a day or once a week, simply observing the symptoms can be very time consuming, not to mention boring and costly. A data logger for resistance can greatly reduce the amount of time spent on the site. The Metex M-3860D multi-meter can be used for this purpose. The Metex meter comes with a floppy disk containing software to write a log file to a disk. It is possible to run the logger from the disk or to install it on your hard drive. There is a read-me file with instructions. There is a setup.exe on the disk that will create a Metex folder on the C drive and install the software there. This will also be the default location for log files. The software is old. It was made for a PC-386 with windows 3.0. It does seem to run on a PC

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with Windows XP-pro. The software is fairly simple and easy to use. There are basically three things that need to be done. 1) Create a file for the log. 2) Specify a sample interval (maybe every second). 3) Set up a sampling Hi and Lo limit. To start, set the limits to about +/- 3-5 ohms of the normal or expected resistance. For example if the resistance, when the link is working well, is 63 ohms set the limits to 60 and 66. Samples can be saved either between the limits or outside the limits. Check the radio button to log samples outside the range. The software will now log values that are either too high or too low.

Some resistance examples:

Figure 1. Resistance at several points along properly terminated, intact, LonTalk links of two different lengths.

Figure 2. Resistance of a LonTalk link that is intact and properly terminated (above). Resistance of the same link that is open at one end because the termination resistor is loose or missing (below). If the termination resistor is loose the connection may be open only intermittently. The resistance will fluctuate and communications may be up and down. Resistance and communications may fine for long periods of time. The break could be anywhere. The symptoms will be similar but it will be harder to find and fix.

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3000 ft at .0162 /ft ~ 49

105 105

69 77 69 72

2500 ft at .0162 /ft ~ 41

105 105

72 73 67 67

2000 ft at .0162 /ft = 32

105

65 69

105

65 68

2000 ft at .0162 /ft = 32

105 105

105 137 169 121

Figure 3. Resistance on a link with extra termination resistors and/or a branch. Above is resistance that should be seen at different points on a 5000 ft link that has the correct topology and is properly terminated. Below are two links with a total of 5000 ft of wire but that have branches with extra termination resistors. The resistance is much lower than it should be given the amount of wire but it is not low enough to indicate a short. Values in the low 50s can be hard to interpret because it could be a reasonable value from a very short link.

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3800 ft at .0162 /ft ~ 62

105

105

105

500 ft at .0162 /ft ~ 8

700 ft at .0162 /ft ~ 11

5000 ft at .0162 /ft ~ 81

105 105

75 93 75 89

2500 ft at .0162 /ft ~ 41

1250 ft at .0162 /ft ~ 20

105 105

105

Part IV: One possible approach and some examples.

The main points:1) The shorter the link the easier it will be to find and correct problems. Divide and

conquer. Isolate segments of the link, check resistance and look for CRC errors. 2) Use Rover to collect transmission error counts from devices on isolated segments at the

same time. 3) Segments that have CRC errors and/or resistance that is too high or too low probably

have at least one problem. Narrow the search until the problem is found.4) If the problem is intermittent make sure that segments are kept isolated long enough to

detect any problems that may exist there. 5) Correct the problem or problems and move to a new segment of wire.6) Double-check for additional problems. Avoid duplicated efforts.

The basic idea:This strategy is just one of many that can work. It has the advantage of being straightforward and systematic. The idea is to establish a section of the link at one end that has no symptoms, and to then expand that section incrementally toward the other end, until the whole link has no symptoms.

Chose a place to divide the link. If there is information suggesting a problem at particular location it might make sense to start there. If problems began only after devices were added to the link it makes sense to begin with that part of the link. If it is possible to make this first division such that a substantial part of the link has no symptoms it will save a lot of work. Otherwise, someplace near the middle would be a good choice. If there are a lot of problems it may be better to start at one end. If there is no prior information about the location of problems, repeatedly dividing the link in half results in the fewest moves.

Physically separate the link. Always make sure that both segments have proper termination resistors so they will behave normally and that new problems are not created by improper termination. If the wire is shielded take care to ground it properly. The wire can be separated and new termination resistors installed on both sides. This is the simplest thing to do, but status and control will be lost to devices on the far side of the break. A Trane repeater could be installed. A Trane repeater divides the link electrically but all messages, including corrupted messages and noise, are passed. Thus a protocol analyzer will not be a useful diagnostic tool in this case. A recording multi-meter like the M-3860D would still be useful. A better option is to use a smart switch such as the Loytec LS-33CB. This allows both a protocol analyzer and multi-meter to be used effectively. Function of the site will not be further compromised by the troubleshooting process. Status and control can still be maintained.

Start to work on one side of the switch. If the BCU is at an end, the side with the BCU probably makes the most sense. If the BCU is not at an end, it might be better to start at the other side. Put the protocol analyzer and the recording meter on the desired side of the switch. If there are a lot of CRC errors, and/or if the resistance is either too high or too low, move the switch half way closer to the end. Move the protocol analyzer and recording meter. Continue to move toward

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the end until both the number of CRC errors get close to zero, and the resistance is in the proper range and is stable.

At this point the segment between the end of the wire and the switch is probably ok. When the switch is moved is as important as where it is moved. This will not always be clear-cut, especially if the problems are intermittent. If problems occur once a day, re-divide the link in fifteen minutes will not be productive. Problems will be missed. Using the switch and recording diagnostic tools makes it easier to avoid the pressure to rush.

Now start moving the switch away from the end (back toward the other end). When CRC errors reappear and/or the resistance falls outside the limits there is at least one problem between the current position of the switch and the previous position. Continue to move the switch to narrow down the segment of wire that contains the problem. Once the problem is corrected continue to move the switch away from the end until another problem is detected. Repeat.

Some step by step suggestions and examples: Figure 4 shows a simple and efficient procedure for repeatedly dividing the link into shorter segments. Continue to divide the link in this way until symptoms are isolated on a short segment. Correct the problem. Then repeat the procedure on another section that still has symptoms. Figures 5 and 6 are additional examples that apply the procedure. Keep in mind that not everything here will be useful or necessary at every site. Use site specific information and insight to modify as appropriate.

1) Document the problem. Assemble information from Summit Event log and trends. Look for and note any patterns. Get a map of the site with the locations of controllers. Make a list of controllers with their NID, location label, Summit object name, and DSN address. Create a spreadsheet to record resistances.

2) Confirm the location and size of termination resistors. Make sure the connections are good.

3) Measure resistance of the whole link. Go to one end of the wire. Keep track of this point on the link by giving it a name, in the examples End EA. At point EA, measure resistance with the link intact. This is a parallel resistance with one termination resistor on one side and the other termination resistor plus some wire on the other side. Write this on the map. Enter this value in the resistance spreadsheet. Remove the termination resistor at point EA and measure the resistance. This should be a series resistance that equals the value of the termination resistor at the far end plus the resistance of the wire. Add this resistance to the spreadsheet. Replace the termination resistor at EA. Go to the far end of the link. Give it a name for the spreadsheet, in the examples End EB. Repeat the measurements at EB and put the values in the spreadsheet. Replace the termination resistor. These values should be exactly the same as they were at EA. Compare the measurements with Table 1 above. Does it make sense considering the amount of wire?

4) Connect a protocol analyzer and recording ohm meter to the whole link. Look for CRC errors and fluctuating resistance. Document what you observe. Presumably the whole link will show CRC errors and/or abnormal resistance. If not it may make sense to leave the analyzer and meter in place for observation.

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5) Divide the link with a LonTalk switch like the Loytec LS-33-CB. Name the point for the spreadsheet, in the examples S1. Put point S1 on the map. Now there are two segments, EAS1 on one side of the switch and S1EB on the other side.

6) Measure resistance on segment EAS1 as in #3. Record in the spreadsheet. 7) Move to the other side of the switch. Measure resistance on segment S1EB as in #3.

Record in the spreadsheet. Use Ohms law to make sure that the resistances on segments EAS1 and S1EB are consistent with the resistance on the parent segment (in this case the whole link EAEB). The resistance due to wire on the two segments should sum to the resistance due to wire in the whole segment. Parallel resistance should be consistent with the resistance due to wire and the two termination resistors on each side.

8) Put the protocol analyzer and meter on segment EAS1. It might be immediately apparent that there is a problem on EAS1. But if the problem is intermittent it may be necessary to leave the equipment in place for a period of hours or days in order to determine whether or not there is a problem on EAS1. Relate observations to the Summit event log and trends. If there are no symptoms on segment EAS1 move directly to the other end, segment S1EB.

9) If there are symptoms on EAS1, that is if there are periods of time when there are a lot of CRC errors or when the resistance fluctuates or is too high or too low, move the switch to a point between S1 and EA. Call this point S2. Termination resistors could be added at point S1. In this case the new segments are EA to S2 and from S2 to S1, in addition to the old segment S1EB. Alternatively reconnect the wire at point S1. Now the new segments will be EA to S2, and from S2 to EB (the old segment S1EB is absorbed into S2EB).

10) Measure resistance on both the new segments EAS2 and S2S1 (or S2EB) and record in the spreadsheet and on the map. Use Ohms law to make sure that the resistances on the new segments EAS2 and S2S1 (or S2EB) are consistent with the resistance on the parent segment EAS1 (or EAS1 and S1EB).

11) Move the protocol analyzer and recording meter to segment EAS2 (the side of the switch nearest the end at point EA.

12) Repeat steps 8-9 with segment EAS2, creating new segments EAS3 and S3S2. If symptoms are not seen move to segment S2S1 (if termination resistor was added at S1) or segment S2EB (if the wire was reconnected at S1).

13) Continue to move the switch toward the end at point EA, creating new segments EASn and SnSn-1, and recording measurements as in the steps above. Do this until the segment between the end at point EA and the switch, EASn, has no symptoms.

14) Here is what we know about the location of problems at this point: Now there will (hopefully) be a section at one end of the link, between point EA and the current location of the switch Sn, that has no problems. There will also be a series of segments between the current location of the switch Sn and point S1. There is at least one problem between the current location of the switch Sn, and the previous position Sn-1 because there were symptoms on the parent segment. There may also be additional problems between the previous location, Sn-1, and point S1. We don’t know anything about the segment between S1 and the other end of the link at EB because we have not looked there yet.

15) Now extend the section that has no problems back toward point S1 and then finally to the far end of the link at EB. First, work on the segment where there is a known problem, SnSn-1. Move the switch to a new location, Sn+1, between the current location Sn and the last location Sn-1. Measure resistance and record. Put the protocol analyzer and meter on

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the wire between the new location for the switch Sn+1, and the end of the link at point EA. If there are symptoms divide SnSn+1 and repeat the procedure. If there are no symptoms move to the other side of Sn+1, the Sn+1Sn-1 segment, and repeat the procedure.

Figure 4. Systematically divide the link into successively shorter segments. On each new segment measure resistance and look for CRC errors. Use Ohm’s law to make sure that resistance on each new segment is consistent with the parent segment. Work toward one end of the link (in this case End EA) until no symptoms are seen on the section closest to the end. It may sometimes be more convenient to deal with parts of the link at a time. Isolate sections physically with termination resistors and treat each part separately. The points S1, S2, … Sn represent the successive positions of the switch on the link as a whole (above) and on the various segments (below). In practice the positions for the switch Sn will probably not always increase to the left as above. As problems are fixed the switch is moved back and forth on new segments to isolate additional problems as in examples 5 and 6.

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105

69 77

105

69 75 3000 ft at .0162 /ft ~ 49

S2S3 S1S4

End (EA)

End (EB) Divide

105105

Switch (S1)

1500 ft at .0162 /ft ~ 241500 ft at .0162 /ft ~ 24

105

62 62

105

62

End (EA) End (EB)

105

Switch (S2)

750 ft at .0162 /ft ~ 12750 ft at .0162 /ft ~ 12

105

105

105

End (EA) S1

Continue dividing as needed Switch (S3)

375 ft at .0162 /ft ~ 6375 ft at .0162 /ft ~ 6

105

105

105105

End (EA) S2

Divide

Divide

Figure 5: An example of the basic method and suggested steps outlined above. The example is idealized. In practice the presence or absence of symptoms on particular segments may be less clear-cut than in the example. When problems are intermittent confidence in the assessment depends on how long we spend watching. As the link is divided repeatedly the most recent, shorter, segments may be left terminated for only a short time giving less confidence in these results. This affects decisions about where to move the switch and whether, or for how long, segments are left terminated before reconnecting. A conservative approach reconnects the link, keeps the site running and minimizes mistakes. The most conservative approach would be to essentially consider only the two segments currently on either side of the switch (in other words the link is always reconnected). It would ignore low confidence information about shorter sub-segments that are nested within.

I. Resistance is too high and/or fluctuating on the link as a whole. The protocol analyzer and individual devices are recording many CRC errors. The Summit event log has many communication failures.

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Bad Crimps

105 105 105 105

CRC

188 ft at .0162 /ft ~ 3

Switch (S4) S3

188 ft at .0162 /ft ~ 3

S2 CRCBad Crimp

Divide

Bad Crimps

105 105 105 105

CRC

94 ft at .0162 /ft ~ 1.5

Switch (S5) S4

94 ft at .0162 /ft ~ 1.5

S2

No Symptoms

Bad Crimps

105 105 105 105

CRC

94 ft at .0162 /ft ~ 1.5

Switch (S5) S4

94 ft at .0162 /ft ~ 1.5

S2 CRCBad Crimps

Replace Crimp

V

VI

VIIDivide

105 105 105 105

End (EA) End (EB)

Bad CrimpsCRC 1500 ft at .0162 /ft ~ 24

1500 ft at .0162 /ft ~ 24

Switch (S1)

Bad Crimps

105 105 105 105

End (EA)

CRC

750 ft at .0162 /ft ~ 12

Switch (S2) S1

750 ft at .0162 /ft ~ 12

Divide

No Symptoms

Divide

No Symptoms

Bad Crimps

105 105 105 105

CRC

375 ft at .0162 /ft ~ 6

Switch (S3) S1

375 ft at .0162 /ft ~ 6

S2 CRCBad Crimp

Divide

3000 ft at .0162 /ft ~ 48

105 105

End (EA) End (EB)

Bad CrimpsCRC

Divide I

II

III

IV

II. The link is divided in the middle with a Lon switch at S1. There should now be two properly terminated links EAS1 and S1EB. Resistance is measured on S1EB and is consistent with a properly terminated link of 1500 ft. and there are very few CRC errors. The left side of the switch EAS1 still has symptoms. Now we know that there is at least one problem between EA and S1 but that S1EB has no problems. III. Move the switch to S2, the midpoint of the segment with symptoms, EAS1. There are now three terminated segments, EAS2, S2S1, as well as S1EB from the previous division. Measure resistance and check for CRC errors on the two new segments. Resistance on EAS2 is consistent with a properly terminated link of 750ft and there are few CRC errors. Segment S2S1 still has high and/or fluctuating resistance and many CRC errors. There are now two segments that show no symptoms, EAS2, and S1EB. All the problems are now isolated on a 750 ft segment in the middle, S2S1. If the terminator is removed at S1 and the link reconnected, the whole comm. link can remain functional since the switch is at the only division point. IV. Move the switch to S3, the mid-point of S2S1. There are symptoms on both the new segments S2S3 and S3S1. (If the terminations are left in place at S2 and S1 we can look at S2S3 and S3S1 directly. If the link was reconnected at S1, so that it could continue to function, the segment to the right of S3 would actually be S3EB. However, we know that the problems on S3EB are all to the left of S1 since S1EB had no symptoms. Similarly, the link could have been reconnected at S2 so the segment to the left of S3 would be EAS3. We know there are no problems to the left of S2 so all the problems on EAS3 must be between S2 and S3. Reconnecting the link certainly makes sense so the site can continue to function. Logically it does not matter if the link is reconnected or not when the switch is moved. However it is probably a good idea to always measure and record resistance, and to look for CRC errors, on all segments before they are reconnected in order to gather as much information as possible.) V. Move the switch to S4, the midpoint of S2S3. There are symptoms to the left of S4. The problem or problems are to the right of S2 and to the left of S4. We know this either because the link was left terminated at S2 so we are looking at S2S4 directly, or because there were no symptoms to the left of S2 when the switch was at S2. There are also symptoms to the right of S4. When the switch was at S1 we determined there were no problems to the right of S1 so the problem or problems are between S4 and S1. If the link was reconnected at S3 we can’t tell if the problems are between S4 and S3, or between S3 and S1, or both. If the termination was left at S3 we can determine that there are no problems between S4 and S3. VI. We know there is at least one problem on S2S4 so move the switch to the midpoint at S5. There is a problem on S2S5. At this point the segment is less than 100 ft. It may not be realistic but in this example it was possible to find and correct a bad crimp connection on this relatively short piece of wire. The segment is retested and this corrected all the problems on S2S5. Now we know that the segments EAS5 and S1EB are ok. There is at least on problem on S5S1. VII. Continue to divide the remaining segment(s) until all the problems are corrected.

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Figure 6: In this example the link has branch. It is terminated incorrectly by either the Trane (daisy chain) standard or by Echelon’s less restrictive standard. The total length is too high (5700 ft.), although initially we probably don’t know this. The link as a whole may well have communications failures. Resistance will certainly not be in the expected range. In the pictures red arrows indicate a segment that contains the branch and has low resistance. The drawings show the link remaining separated after each division.

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1800 ft at .0162 /ft ~30

105 105

700 ft at .0162 /ft ~ 11

105

DivideS1 End (EA)

4300 ft at .0162 /ft ~ 70

105 105

700 ft at .0162 /ft ~ 11

End (EB)

105

700 ft at .0162 /ft ~ 11

S1S2S3 S4

Divide End (EA)

105 105

105

105 105

2500 ft at .0162 /ft ~ 41

700 ft at .0162 /ft ~ 11

1800 ft at .0162 /ft ~ 30

End (EA) Switch (S1)

105 105 105 105

Switch (S2)

1250 ft at .0162 /ft ~ 20

700 ft at .0162 /ft ~ 11

550 ft at .0162 /ft ~ 9

S1 End (EA)

105

I

II

III

IV

550 ft at .0162 /ft ~9

105 105

700 ft at .0162 /ft ~ 11

End (EA) Divide S2

700 ft at .0162 /ft ~ 11

105

550 ft at .0162 /ft ~9

105 105

700 ft at .0162 /ft ~ 11

DivideS2

105

75 ft at .0162 /ft ~ 1

S3

105 105 105 105

Switch (S4)

313 ft at .0162 /ft ~ 5

700 ft at .0162 /ft ~ 11

240 ft at .0162 /ft ~ 4S2

105

75 ft at .0162 /ft ~ 1

S3

105 105 105 105

Switch (S3)

550 ft at .0162 /ft ~ 9

700 ft at .0162 /ft ~ 11

625 ft at .0162 /ft ~ 10

S2 End (EA)

105

75 ft at .0162 /ft ~ 1 VI

VII

VIII

Obviously communications to the BCU will be down to at least some devices as long as there are divisions other than at the switch. The link can be reconnected to restore communications as soon as we are confident which segments have symptoms. If this is done carefully the conclusions outlined below are still valid. I. The initial intact link with observed resistance. The successive positions of the switch are S1, S2, S3, S4. II. The link is divided with a switch at S1. To the right, on S1EB, resistance appears to be normal. To the left, on EAS1, resistance is still too low. III. The segment that still has symptoms, EAS1, is divided again at S2 to give IV. IV. Resistance is ok on the new segment S2S1. Resistance is too low on EAS2. So we know there are no symptoms between S2 and EB and there is at least one problem between EA and S2. V. EAS2 is divided at S3 to give the new segments EAS3 and S3S2 (VI).VI. The switch has now been moved to the left of the branch. We know the problem is to the right of S3. We know there are no symptoms to the right of S2 from II and IV so the problem must be between S3 and S2. EAS3 and S2EB are ok. VII. S3S2 is divided to give new segments S3 S4 and S4S2 (VIII). VIII. The problem is now again to the left of the switch. The good part of the link is extended from S2 to S4. We know from VI that everything to the left of S3 is also ok. So the problem is between S3 and S4. Four divisions have narrowed the search to a little over 300 ft of wire. Once the branch is located installing a repeater should solve the problem. The repeater will be in the middle of a 1400 ft link. There will be 4300 ft of wire on the other side of the repeater. If it is terminated correctly, the link will now conform to the recommended wiring practices.

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troubleshooting lontalk wiring sec i, ii, iii, iv.updted

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