Troubleshooting Lookout Communication
- Why can't I communicate with my PLC/RTU?
There could be several reasons. First of all, are you using the right driver (e.g. Modbus and not ModbusSlave)? Do you have the latest driver? Please check our Drivers and Updates Library for the latest drivers. If your driver is not listed, then there hasn't been any update to it.
- I get the "Garbled Communication Response" alarm.
Go into your Options » Serial ports menu. Here, increase the Receive Gap setting to 20 or more. The Receive gap setting is available for all serial connection types. This number specifies
the number of empty bytes (or amount of time) a driver receives from a controller before the driver recognizes the end of a message frame and asks for another message. Normally you should leave this at the default setting. However, if you are experiencing garbled communication alarms, you might try increasing this number to allow more dead time before Lookout decides it has received a complete message. For example, with a slow baud rate of 1200, you might have to increase the Receive gap setting to approximately 30.
- I get the "No response within timeout period" alarm
Lookout did not receive the expected response within the Receive timeout period. The object sent an inquiry and received an acknowledgment, but the device did not send an expected response to the request. This might happen if the response was interrupted. You may have to increase the Receive timeout.
- I get the "No communication (or No return inquiry) response
from secondary unit" alarm
Lookout received no response from the device within the Receive timeout period. The driver object is able to use the COM port, but when it polls the device, there is no response—-as if the device is not even there. You may have to increase Receive timeout to ensure Lookout is allowing enough time to receive the expected response. Also, verify your baud rate settings, cable connections, power, configuration settings, COM port settings, and polling addresses. These should be exactly the same as you've defined using the PLC's programming software. Last but not least, check for
the physical connection of the cable from the correct COM port to your device.
- I don't get any of the above alarms. I get a different alarm.
The above alarms are the most common communication alarms. However, you may be getting a different alarm. Please refer the Lookout Reference manual for documentation on the particular driver for any driver-specific alarms and their solution.
- I don't get any alarms at all. But, I don't think I am communicating either.
You will not get any alarms till you poll the device. So, insert an Expression on any valid register.
A good idea is to trend the Update member on HyperTrend. This is very helpful to check whether polling occurs at the specified poll rate or there's some discrepancy. Next, force a poll by tying a pushbutton to the Poll data member.
Also make sure that you are not filtering any alarms. Select Alarms » Filter Options » Display All.
- I am not sure if I can communicate with the PLC's programming software either--I haven't tried.
You'll first have to try establishing communication with the proprietary programming software for the PLC. Then, make a note of all the settings therein, like, baud rate, parity, etc. Clone these settings in Lookout--exactly! Are you using exactly the same settings? Check again!
- I can communicate with the PLC's proprietary programming software, but not with Lookout.
Is that software running now? If so, shut it down. Either Lookout or the programming software
can communicate at one time, but not both. Make sure you're using exactly the same communication settings in Lookout as in the proprietary software.
- I am using a modem. Are there any special settings that I need to address?
Check the serial port settings under Options » Serial Ports for correct "Serial port" (that is, the COM port to which your modem is connected). Make sure that you have selected either Dial-up or Radio as the "Serial connection."
In the Dialing Prefix setting insert "M2L3" so that you have an audible feedback when the modem dials out. Check the documnetation on your modem for specific instructions on the dialing prefix.
- What next?
Are you using any other hardware? Converters? Adapters? Does the driver need a plug-in card? E.g., ModbusPlus (SA-85), Applicom, etc. Do you have the interface card? And the driver? Please consult the Lookout Reference Manual for further details on the PLC object class you are using.
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