I am currently overseeing a manufacturing process that involves an IPC, multiple PLCs, and various drives all interconnected through a CAN network. Yesterday, we encountered several communication alarms across the network. To troubleshoot the issue, I first checked the voltage levels on the CAN high and low lines, which were within the appropriate range: CAN H measured between 2.6 to 2.9V and CAN L between 2.1 to 2.5V. I then powered down the system and tested the resistance between CAN H and CAN L, which showed a reading of 43 ohms. Given that there should be two 120-ohm terminating resistors at each end, I expected the reading to be around 60 ohms. One aspect that puzzled me was the presence of multiple CAN adapters. Some of these adapters split the CAN signal into separate loops, each with its own set of resistors. I am unsure whether these additional loops and resistors form distinct networks or if they are part of the network under investigation. The specific network I am addressing is highlighted in green boxes in the provided image, while the other loops connected to the same adapter are marked in red. I am uncertain if these additional loops have any impact on my network since they originate from the same adapter. After observing the 43-ohm resistance reading, I suspected that superfluous resistors might be influencing the network. To test this theory, I disabled the terminator switch at the last node, which raised the network's resistance to 70 ohms. Surprisingly, this action resolved the communication issues. While it is standard practice for the last node to have its terminator enabled, this adjustment brought the network's resistance closer to the expected 60 ohms, temporarily solving the problem. Currently, I am seeking to identify the root cause of this issue. I would appreciate insights on the following questions: What could have caused the 43-ohm resistance measurement in the loop? Do the additional loops/devices attached to the CAN adapters impact the network I am analyzing? Why did deactivating the last resistor switch restore communication, even though my network initially only had two terminators? Was this switch the key factor in aligning the network resistance around 60 ohms?
Hello aamirawan91, I share the same inquiry mentioned in paragraph 2 of your initial post. Do you know the part number of the CAN adapter provided by the machine builder? Have they included any manuals or datasheets for this component? If not, could you please share a picture of the device? This way, someone may be able to identify it and offer a user manual for reference.
While I may not have the exact part numbers, I can provide a visual reference. The grey CAN cable runs from the IPC (the initial device) and terminates downward. Above this cable, there are two connectors (male and female) that split into two separate loops with the use of green cables. In the image, one of the cables appears to be unplugged from the female connector. A terminating resistor is located at the center, with a switch above it to toggle the resistor on or off.
Thank you for sharing the picture with us. Unfortunately, the part number of the product is not clear, which makes it challenging for others to identify it. Based on my initial observations, it appears to be a passive CAN coupler with two SDSub9 connectors, two sockets for direct screw connections, and a terminator resistor that can be activated with a jumper. If my interpretation is accurate, it suggests that there are only two adapters with the resistor activated, positioned at the two farthest nodes. However, I am puzzled by the discrepancy between the two drawings. I cannot locate the "CHILL ROLL" device on page one as shown on page two. For proper termination, the resistance between CAN_H and CAN_L should be 60 OHM. In order to provide more specific recommendations regarding the termination location, it would be helpful to see the complete network layout. This will allow us to determine the optimal placement for the terminator.
Thank you so much for your input, AlfredoQuintero. I appreciate your insights on the adapter being one segment. After discovering a mistake in the drawing, I reached out to the OEM who promptly apologized and provided a corrected version. This particular drawing had me puzzled for quite some time!
Hello aamirawan, absolutely no problem. If you find a solution, please keep us informed. If you encounter more issues, I can suggest a cost-effective solution to gather additional diagnostic information. It appears that the issue may be related to termination, as indicated in previous discussions. If you verify the machine builder's design and align the wiring accordingly, and there are no more communication errors, you can be quite confident (although not guaranteed) that your system will operate smoothly. Following proper wiring rules, CAN is highly robust. Best of luck to you.
From your analysis, it appears that there may indeed be additional terminating resistors on your network that are causing a low resistance reading, lower than the expected 60 ohms. The extra loops you mentioned, if they aren't isolated, could definitely be contributing to this, as they're sharing a common connection point. Alternatively, there could be an additional terminator switch that is mistakenly left enabled somewhere within your network. Disabling the terminator switch at the last node likely restored communication due to reducing the impact of these superfluous resistors, hence increasing the total resistance. You are right that it's generally practice to have the last node with its terminator enabled, but in this case, that extra terminator may have been unnecessary, given the presence of the superfluous resistors. I would advise a thorough checking of your CAN network and the additional loops to ensure they're correctly isolated. Also, look out for any unintended resistors on the network that could be affecting resistance measurements.
In my experience working with CAN networks, if you're getting a 43 Ohm resistance reading, it usually indicates that there is an additional terminator (120 Ohm) somewhere on the network line. The extra loops and devices you mentioned could be potential locations of additional terminators in the setup, possibly introduced unintentionally. When you deactivated the last resistor switch, essentially you took one terminator out of the circuit, which explains the restoration of communication. As far as I understand from your description, the switch seemed to align the network resistance closer to the expected 60 Ohms, which suggests it is a critical factor to consider. The network topology and schematics could really help to understand and get to the root of the problem, so it might be worthwhile to study and trace that in detail. Keep us posted on your findings!
It sounds like you’ve really dived deep into the troubleshooting process! The 43-ohm reading could suggest that the additional loops and their resistors are indeed affecting the overall resistance of the network, likely due to multiple paths for the signals to travel. It’s possible that the additional loops created a scenario where the termination resistance was too low, causing reflections or interference that you encountered as communication alarms. By disabling the terminator switch at the last node, you may have inadvertently reduced the total resistance to a more optimal level, mitigating those reflections. It's interesting how the dynamics of networks can change with only a small adjustment like that! Have you considered mapping out the entire network to visualize how the devices and resistors are interconnected? That might help clarify their impact on your main loop.
It sounds like you're dealing with a tricky situation! The 43-ohm reading could indicate that there is an additional unintended path in the network, potentially from one of the extra adapters or loops you mentioned, which might be contributing to the lower-than-expected resistance due to the extra resistors they introduce. As for whether those additional loops affect your network, they definitely can; if they're not configured correctly or overlap with your main CAN loop, they could create signal reflections or interfere with communication. Deactivating the last terminator switch likely helped to balance the network resistance by reducing the total load on the bus, allowing for clearer communication. It's curious how sometimes these adjustments can lead to a more acceptable resistance, even if it strays from the norm. Have you considered visually mapping out the entire network to pinpoint where those additional paths might be influencing your setup? That might shed some light on the root cause!
It sounds like you're doing a thorough job troubleshooting! The 43-ohm reading could indicate that the additional resistors from the other loops were creating an unintended load on the network, leading to lower resistance than expected; it’s definitely worth checking each adapter and loop configuration to see how they’re affecting the main network. Regarding the switch at the last node, disabling it likely helped balance the overall resistance, suggesting that those additional resistors were essentially 'over-terminating' the loop, which as you saw, can cause communication issues. It might help to explore the wiring diagram for your setup to gain clarity on how everything is interconnected—sometimes visualizing the entire system can reveal potential conflicts!
It sounds like you’ve done a thorough job troubleshooting and isolating the issue! The 43-ohm reading suggests that perhaps the additional loops or resistors are indeed creating an unintended impact on your network's overall impedance. When you have multiple branches off a CAN adapter, those extra components can introduce additional resistance or create reflections that mess with the CAN signals. Disabling the last terminator likely minimized the total capacitance and resistance seen by the bus, allowing it to stabilize. It's interesting how small adjustments can lead to significant improvements in network performance! I’d recommend checking the configurations of those additional loops to see if they might need to be re-evaluated or adjusted to avoid similar issues in the future.
✅ Work Order Management
✅ Asset Tracking
✅ Preventive Maintenance
✅ Inspection Report
We have received your information. We will share Schedule Demo details on your Mail Id.
Answer: - The 43-ohm resistance measurement in the loop could have been caused by the presence of additional loops with their own resistors, superfluous resistors influencing the network, or possibly a faulty connection affecting the overall resistance.
Answer: - Yes, additional loops and devices attached to the CAN adapters can impact the network being analyzed, as they introduce extra resistors and can alter the overall network resistance and communication behavior.
Answer: - Deactivating the last resistor switch likely restored communication by adjusting the network resistance closer to the expected value of 60 ohms. The switch may have been a key factor in aligning the resistance properly, especially if the presence of additional loops and resistors was affecting the network performance.
Join hundreds of satisfied customers who have transformed their maintenance processes.
Sign up today and start optimizing your workflow.