Communication Errors Troubleshooting

When the MC-III EXP or MC-III WP is connected properly with a good quality RS-485 adapter, communication errors should be rare. Depending upon your timeout settings, the layout of your wiring, or even the processing load on your Windows operating system, you may experience the occasional communication error; to resume operations, click Retry in the Communications Problem dialog box. However, if you are having consistent communication errors, there is a problem that needs to be addressed.

The following is a list of possible problems and solutions. If you cannot resolve the problem after trying these solutions, contact technical support. Please make a note of all troubleshooting steps attempted and of the results, and be prepared to discuss this information with technical support.


Express Connect Problems Express Connect allows the program to detect the MC-III regardless of the device's baud rate and slave address settings. If you are not able to connect to the MC-III with Express Connect, try the Connect Device At Address menu item under the File menu to specify the slave address and baud rate. Express Connect is not recommended for connecting to multiple instruments.
Multiple Device Networks The Express Connect method is not recommended when connection to multiple instruments. For multiple device networks, use the Connect Device At Address or Discover Modbus Slaves connection methods. Each MC-III in the network must have a unique slave address.
Bad Connection Check that the connections between your computer and your RS-485 adapter, and from your adapter to the MC-III, are secure. Also, confirm the polarity of the wiring from the converter to the instrument. For more information on wiring the converter, refer to the MC-III Quick-Start Guide or the MC-III EXP or MC-III WP User Manual.
NuFlo USB Driver Issues

If the MC-III is equipped with a NuFlo USB Adapter but the NuFlo USB Adapter does not appear as a COM port selection in MC-III software, verify that the NuFlo USB driver has been installed per the instructions provided. If the driver is properly installed, see the NuFlo USB Adapter Troubleshooting Tips for help in identifying other possible causes of driver-related connection problems.


Power Problem Check that the MC-III is receiving adequate power, and that the power connections are secure.
Optimal Timeout Period Too Short

Depending on your computer's hardware and software characteristics, and the characteristics of your device network, the default optimal timeout periods may be too short. To extend the optimal timeout period, enter a value into the Timeout Period field in the Communications section of the Program Options dialog box. By default, there is 0% extension. If you extend the timeout period by 100%, you will double the optimal timeout period. Extending by 200% will triple the timeout period, and so on. You may also change the Timeout Period Type to Fixed, and enter your own timeout period.

  A long timeout period does not directly affect the time required for the device to respond, only how long the program will wait for a response before giving up and reporting an error. If you specify a long timeout period, you will wait longer for the program to return control to you when communication errors do occur.
Fixed Timeout Period Too Short If you use a Fixed Timeout Period Type, you may need to increase the Timeout Period. See Optimal Timeout Period Too Short for more information.
Line Noise Check that your RS-485 wiring is not routed near sources of electrical noise, such as electric motors. If minor line noise cannot be avoided, it may be helpful to lower the baud rate of the device. Increasing the number of retries in the Communications section of the Program Options dialog box may also help.
Not Enough Retries If the program does not receive a valid response from the device within a timeout period, the program will automatically resend the message a certain number of times before finally reporting a communications error. By default, the program will re-attempt each communication two times before it gives up. To increase the number of retries, increase the value in the Number of Retries field in the Communications section of the Program Options dialog box. Line noise can corrupt messages exchanged between the program and the device, and increasing the number of retries can improve the chances of a successful connection.
  Setting a high number of retries will not directly affect communications speed when there is a good connection, since there would be very few actual retries. However, setting a high number of retries will result in longer waits for the program to return and report an error when there are communications difficulties.
Specific Baud Rate Required If you are using a radio link, a virtual COM port, or an Ethernet serial converter, ensure that the baud rate set in the device is supported by the intermediate link.
Baud Rate Too High If you have a long wiring network, have many devices on your network, or have line noise, try a slower baud rate to achieve reliable communication to your devices.
Auto-negotiated Baud Rate Too High If you have activated the "Attempt auto-negotiation of fastest baud rate..." feature, and you are experiencing excessive communication errors, the auto-negotiated baud rate may be too high for your network. Auto-negotiation tests all baud rates from 115200 baud down to 300 baud, and selects the highest baud rate that supports successful communications. It is possible that the auto-negotiation test incorrectly determined the fastest baud rate for the network. You can try the "Test Now" button in the Communications section of the Program Options dialog box to see if a lower baud rate can be automatically selected.
  If you continue to have problems, disable the "Attempt auto-negotiation of fastest baud rate..." option; the program and device will only communicate at the device's baud rate at the next connection from the Welcome Screen. Deselect the "Enable auto-negotiated baud rate" to disable any currently active usage of an auto-negotiated baud rate.
Device Bus Delay Too Short Increase the time that the MC-III waits before responding to Modbus commands by increasing the Bus Delay value in the device. You do not need to adjust the program's timeout periods to account for the Bus Delay. This is done automatically by the software.
  In some cases of consistent timeouts, it may be helpful to slow the MC-III's message response rate by increasing the Bus Delay in the device to at least 50 msec to prevent the response from being missed by the software.
Presend Delay Too Short Increase the time that the program waits between consecutive Modbus commands by increasing the Presend Delay value in the Communications section of the Program Options dialog box.
Device Parameters Changed While Connected If you manually change the communications parameters (slave address, baud rate) of the MC-III from the instrument keypad, the program will not detect the change. Return to the Welcome Screen and re-connect to the device.
RTS Control Not Properly Set Your RS-485 adapter may require that the RTS line of the COM port be toggled to control the direction of data flow for transmit and receive. If so, ensure that the "Toggle RTS line" option is enabled in the Communications section of the Program Options dialog box. Alternatively, if you are connected to a modem device on your COM port that requires that the RTS line be used in the standard way for RS-232 flow control, the "Toggle RTS line" option is disabled.
Spontaneous Loss Of Communication If for some unknown reason, the program stops communicating with the MC-III while you are using the program, return to the Welcome Screen and re-connect.
Device Needs To Be Reset If the settings in the MC-III become corrupted or are changed in such a way as to cause the device to fail to communicate with the software, reset the MC-III to factory default settings by pressing the lower three buttons on the faceplate of the device simultaneously and releasing. The device will load factory default settings and show "DEFALT" on the LCD briefly.
  CAUTION: Loading factory default values will lose all configuration values, such as the K-factor. However, logged data will remain intact.
Restart Program An unexpected software error may have occurred that is interfering with communications. Close the program and run it again. If the problem persists, close all programs and restart your computer.
Windows Too Busy If you are running a large number of programs or a few CPU-intensive programs at the same time as the MC-III Interface program, the processing load on Windows may cause delays in serial port processing. When this happens, the program is not receiving data from the COM port fast enough, even though the data was transmitted by the device in time, and timeouts will occur. Reduce the load on Windows by closing some of the other programs.
  Switching between programs also increases the operating system load by causing Windows to perform various system activities. If you switch away from the MC-III Interface while it is busy communicating with the device, it may cause a delay in Windows delivering data from the serial port to the program. Also, when the MC-III Interface is in the background, it receives a smaller percentage of the CPU's processing time, and will run more slowly. If the program is in the process of completing a communication-intensive operation, this reduction in processing power may cause communication problems. If you notice problems when you switch away from the MC-III Interface, close the other programs, or keep the MC-III Interface in the foreground while it is being used.
  Systems with faster CPU's and more memory will be less likely to experience these types of problems.

Contacting Cameron

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Cameron
Measurement Systems Division
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www.c-a-m.com/flo/

 

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