Telegraf requesting from multiple modbus slaves

1

I have been using influxdb for a while, and have decided to give telegraf a try now that it supports modbus.
I have a RS-485 serial bus with 5 modbus slaves with different slave_ids. My test setup uses nodejs/node-red and requests data with intervals of 10s to 60s, with only a few registers per modbus slave.
By stopping my test setup and switching to telegraf I have to configure the [[inputs.modbus]] 5 times in order to request from 5 different slave_ids.
To me it seems like they are running in parallel and trying to access controller = “file:///dev/ttyUSB0” at the same time, giving: [inputs.modbus] Error in plugin: serial: timeout
With collection_jitter set, there is also correct readings, but randomly ~40% timeouts

[[inputs.modbus]]
name = “Dummy1”
slave_id = 6
timeout = “1s”
controller = “file:///dev/ttyUSB0”
baud_rate = 19200
data_bits = 8
parity = “E”
stop_bits = 1
transmission_mode = “RTU”
input_registers = [
{ name = “Dummy1”, byte_order = “AB”, data_type = “UINT16”, scale=1.0, address = [4]},
]
[[inputs.modbus]]
name = “Dummy2”
slave_id = 7
timeout = “1s”
controller = “file:///dev/ttyUSB0”
baud_rate = 19200
data_bits = 8
parity = “E”
stop_bits = 1
transmission_mode = “RTU”
input_registers = [
{ name = “Dummy2”, byte_order = “AB”, data_type = “UINT16”, scale=1.0, address = [2]},
]
… a total of 5

Is there a better way of requesting from 5 slaves?
Is there a way to sequence the requests?

2

It looks like these registers are all from the same device, I think you would want to set it up more like:

[[inputs.modbus]]
  name = "Dummy1"
  slave_id = 6
  timeout = "1s"
  controller = "file:///dev/ttyUSB0"
  baud_rate = 19200
  data_bits = 8
  parity = "E"
  stop_bits = 1
  transmission_mode = "RTU"
  input_registers = [
  	{ name = "Dummy1", byte_order = "AB", data_type = "UINT16", scale=1.0, address = [4]},
  	{ name = "Dummy2", byte_order = "AB", data_type = "UINT16", scale=1.0, address = [2]},
  ]
3

Thanks @daniel
You suggestion works fine on a single modbus slave
This thread is about multiple modbus slaves. I my case 5 different slaves. Each slave with their individual slave_id.

slave_id = 6
...
slave_id = 7
...

… a total of 5 different slave_ids

4

I see, maybe we will need the slave_id to be part of the registers. Can you open a feature request on the Telegraf issue tracker and we can discuss further the best way to support this.

5

Is it possible to run multiple instances of Telegraf all of the staggered by different sampling intervals - each instance acquiring the data for a single slave and reporting. Would that work?

6

@Samy

I have the same problem and I am running multiple instance one after another by a systemd unit and timer. See: Multiple Modbus terminal Monitoring · Issue #7523 · influxdata/telegraf · GitHub