I made an initial modbus connection, which was successful. The issue is that the values are not updating, just the first number it polled. I changed and configured the polling settings according to the user manual. I am still not able to get a continuous polling of modbus information. The Modbus PLC is connected to a Moxa (with Ignition edge) device via modbus TCP/IP.
There is no firewalls or anything blocking the data.
Are there any errors in the gateway logs?
You can do a Wireshark capture to confirm, but it looks like the device just isn't responding.
So our edge devices run Debian 9 and for the most part are just confined to the local network, only being able to connect to our MQTT broker.
Is there any other way to trouble shoot this?
And when you say the device isn't responding, do you mean the modbus device? It is an accuload i believe.
They must have at least one tag because his screenshot is showing ReadHoldingRegisterRequests timing out.
Next question is, are you sure your data in the PLC are available in Holding Registers and in the specified addresses? You may try to poll Input Registers.
How do I do that?
Note to self: Moxa is the gateway
By changing the "Modbus Type" in the gateway setting.
The PLC should also have a way to separate these two types of registers.
This is what I have currently. It worked at getting the initial reading, but has not updated since (roughly 2 weeks)
You are getting a timeout. Your device is not responding to Ignition. Take a wireshark capture to see what might be going on. Run another modbus tool on the Ignition gateway and try to replicate.
Knowing what is in the other end is the key. PLC-brand, model,
Modbus is a simple protocol, a ping is normally enough to determine whether the unit is available or not.
Can you ping or connect to the PLC from the gateway?
Ok, so it is available
Can you connect to the IP-address by using port number 502?
Not sure how Ignition determines if it actually is "Modbus"-connected to the PLC, but I expect the verification to be more than a simple ping of the unit. Even if you are able to establish a connection, other conditions must be taken into consideration:
Is the unit setup to receive requests on holding registers, input registers and/or coils? (Function codes?)
How many registers are available in the PLC
Are there any limitations in how many registers you are allowed to read in one poll? There might be limitations in the PLC
Does the start address exist in the PLC? (180 or modbus address 40180?)
I am not very familiar with how Ignition handles Modbus TCP so please arrest me where I am wrong. I do have some experience with Modbus in general though. Modbus Poll is brilliant for testing these conditions.