mylespetro
Member
Hey everyone,
Ran into a bit of an issue with a Modbus RTU radio link on a MicroLogix 1100. Just for context, we have a remote lift station with a CompactLogix doing the control, and we're writing the I/O status to the ML1100 using MSG instructions. I've checked the link there and it's working fine, I can see the I/O updating to match what's on the CPLX/HMI. The ML1100 is then plugged into a Bell 202 modem, which is then being polled from the main water treatment plant over radio, with a straight shot across the harbour, about 1.6km, I can see the antenna on the roof of the WTP standing at the lift station. EDIT: The radio link was set up by a contractor who handles all of the radio links for the municipality and he confirmed a good link, and set up the B202 for 1200 baud.
The SCADA/HMI system at the WTP is VTScada, and I've set up this new station where there was available spaces both in the polling sequence (#16) and node/station addresses (23). I do have the PLC set to be station 23 in the Modbus RTU setup on Channel 0. We were getting Modbus error code 517, which is a comms timeout error. Yesterday we realized that the radio guy just plugged the ML1100 serial cable into a gender changer and then put that into the RS232 port on the modem, so we put in a crossover cable. Once we did that, the chirp on the radio changed and the COMM0 indicator on the LCD display on the ML1100 flashed a couple times, and then again about 90 seconds later, which is the polling frequency of the SCADA system.
After changing the cable, I headed back to the WTP to check the comms in VTScada and we're still getting error code 517. I believe all of the SCADA comms are through a SCADANet B202 modem that is then connected to the PC through port COM6, which I've set as the port for our station as well. I've bench tested the application setup at my desk with identical settings to the deployed application and everything works, but that's using a USB-to-serial adapter on COM3 and then plugged into my own ML1100. I can toggle bits and adjust analogs and watch them change in VTScada with no issues, but the same thing deployed at the WTP (changed back to COM6) doesn't work.
It seems to me like the physical link is good, and that the PLC recognizes it's being polled but either data isn't being sent back or VTScada can't make the connection. Just kind of at a loss with where to go next, this is my first go at Modbus of any sort, as well as serial radio communications. I've worked with radios as an Ethernet bridge, which was super easy to set up, but this isn't working out the same way for me.
Just for info, I have the ML1100 set as follows:
Channel 0
Driver: Modbus RTU Slave
Baud: 1200
Parity: NONE
Node Address: 23
Modbus Data Table File Numbers:
Coils: 0
Contacts: 0
Input Registers: 0
Holding Registers: 9 (Not expanded)
Protocol Control:
Control Line: No Handshaking
InterChar. Timeout: 0
Pre Transmit Delay: 0
Ran into a bit of an issue with a Modbus RTU radio link on a MicroLogix 1100. Just for context, we have a remote lift station with a CompactLogix doing the control, and we're writing the I/O status to the ML1100 using MSG instructions. I've checked the link there and it's working fine, I can see the I/O updating to match what's on the CPLX/HMI. The ML1100 is then plugged into a Bell 202 modem, which is then being polled from the main water treatment plant over radio, with a straight shot across the harbour, about 1.6km, I can see the antenna on the roof of the WTP standing at the lift station. EDIT: The radio link was set up by a contractor who handles all of the radio links for the municipality and he confirmed a good link, and set up the B202 for 1200 baud.
The SCADA/HMI system at the WTP is VTScada, and I've set up this new station where there was available spaces both in the polling sequence (#16) and node/station addresses (23). I do have the PLC set to be station 23 in the Modbus RTU setup on Channel 0. We were getting Modbus error code 517, which is a comms timeout error. Yesterday we realized that the radio guy just plugged the ML1100 serial cable into a gender changer and then put that into the RS232 port on the modem, so we put in a crossover cable. Once we did that, the chirp on the radio changed and the COMM0 indicator on the LCD display on the ML1100 flashed a couple times, and then again about 90 seconds later, which is the polling frequency of the SCADA system.
After changing the cable, I headed back to the WTP to check the comms in VTScada and we're still getting error code 517. I believe all of the SCADA comms are through a SCADANet B202 modem that is then connected to the PC through port COM6, which I've set as the port for our station as well. I've bench tested the application setup at my desk with identical settings to the deployed application and everything works, but that's using a USB-to-serial adapter on COM3 and then plugged into my own ML1100. I can toggle bits and adjust analogs and watch them change in VTScada with no issues, but the same thing deployed at the WTP (changed back to COM6) doesn't work.
It seems to me like the physical link is good, and that the PLC recognizes it's being polled but either data isn't being sent back or VTScada can't make the connection. Just kind of at a loss with where to go next, this is my first go at Modbus of any sort, as well as serial radio communications. I've worked with radios as an Ethernet bridge, which was super easy to set up, but this isn't working out the same way for me.
Just for info, I have the ML1100 set as follows:
Channel 0
Driver: Modbus RTU Slave
Baud: 1200
Parity: NONE
Node Address: 23
Modbus Data Table File Numbers:
Coils: 0
Contacts: 0
Input Registers: 0
Holding Registers: 9 (Not expanded)
Protocol Control:
Control Line: No Handshaking
InterChar. Timeout: 0
Pre Transmit Delay: 0
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