Question

Hi.
I'm using the TRB145 LTE RS485 Gateway device and getting unipolar RS485 signal which have level +2.5V. These signals are required by the standard to be differential and have a voltage of -7V to +12V.
Why is that?
Thank you very much.

Answer 1

Hello,

Could you please share your measuring setup?

There are two ways to measure differential signals with an oscilloscope:

• If you have a two-channel oscilloscope, connect one side of the signal to channel 1, and the complementary signal to channel 2. The ground leads stay unconnected. Since you are interested in the difference between the signals, you want to subtract channel 2 from channel 1. Most scopes provide a way to add or subtract channel 1 and channel 2 inputs. On some scopes you might have to add channel 2, but invert it so that you are effectively subtracting it.
• The other way is to use differential probes, which provides better results without reducing the number of usable channels on the oscilloscope. 

You can also watch this video on differential signals measurements: https://www.youtube.com/watch?v=RDLWQFgJ1uU.

Could you share the purpose for performing these measurements?

Best regards,

Žygimantas
 

Comments

Hello.

I would like to clarify my question.

I am using the TRB145 LTE RS 485 Gateway to receive data from the Internet. I take the received data from the RS 485 port. I would like to know the physical parameters of the RS 485 - the amplitude of the signal and its polarity. According to my measurements, the signal swing is only 2.5 V and it is unipolar.

Is it really true?

Best regards, George.

P.S. I dont know how can I transfer the settings file?