TRB246 RS485 modbus wiring

Networking Solutions
1

Hello,

I’m struggling to set up 2 gas sensors with the TRB246 as I consistently get a timeout error when trying to read them via modbus. They’re both connected to the trb through a daisy chain and I know that all modbus parameters are correct as entered since I tried with USB to rs485 and I can read everything just fine on the laptop.

Is my wiring wrong? I saw on another post that R and D should be bridged. Thanks!

IMG-20251125-WA0034(1)
IMG-20251125-WA0034(1)1920×1093 132 KB

2

Hi Jakob,

I had similar issue with my setup.

I can’t exactly remember what the solution was, but I do remember what the cause was.

  1. The Baud rate was incorrect when polling the Modbus data of our sensors.
  2. The polarity of the wiring was the wrong way around - I only found this out after checking the wires with an oscilloscope.

Also of note in our case the sensor and the Teltonika had to share a single power source so that it could differentiate between the high and low bits.

hope this helps.

3

Hi J_Dev,

Thanks for your help! Baud rate should definitely be correct.

I’ll try again switching the data cables but not likely - did you always reboot when changing the parameters?

Sensors and trb246 don’t share the same power source. I thought it’d be fine if I have ground reference between them. But something I will try!

Best

4

Hi,

Please get the basics right, search the web for rs485 wiring. rs485 is a bus where both ends should be properly terminated with 120 ohm. Some devices have a dips switch for termination. On short lengths you may get away with a single termination.

So, no daisy chaining, but parallel wiring.

This is a first hit that looks reasonable:

5

Hello @Jakob1 ,

Could you please let me know if you still need any assistance?

Best regards,