RS485 full duplex to Adapter with A and B ports

Question

I need to configure a sensor (Thies 3D Sonic Anemometer, Manual: https://www.biral.com/wp-content/uploads/2015/01/4.383x.xx_.xxxUS3D.pdf) via my computer, it has RS485 full duplex and half-duplex capability.

From the wiring diagram I found that there are four pins available: TX+ (pin 5), TX- (pin 2), RX+ (pin 4), RX- (pin 1) for full duplex. For half-duplex pin 2 serves for TX-/RX- and pin 5 as TX+/RX+. Now I only have an RS485 Adapter, which has four ports labelled as A, B, Ground and +5V.

As far as I know, the sensor has last been operated in full duplex mode. Will I damage anything, if I hook pins 2 and 5 to my adapter (YF USB to RS485 adapter: https://www.play-zone.ch/de/yf-usb-zu-rs485-adapter.html)?

How do I know which pin to A and which to B on the adapter side?

Answer 1

This is not universal at all but for the devices I've seen A is usually positive (DATA+) and B negative (DATA-).

So wire TX+ together with RX+ to A and TX- to RX- and B and you're good to go.

If you switch these connection your link won't work (as you have already experienced) but the risk of breaking your hardware is not high (but not unheard of).

I quick glance at the manual of your devices seems to imply that you might need to send commands from your computer before you see an answer:

Master-slave structure, i.e. there is a device in the bus (control, PC...) that performs cyclic enquiry of the data of the individual ULTRASONICs and possibly parameterises the ULTRASONICs.

There is also mention to a device ID, have you checked that?

If you just wire everything, open your terminal and still don't see activity maybe you should take a deeper look at the manual, or if you think your configuration is correct maybe you can take a look at your bus with a scope.