Comunicate with RS485

[Kaliman]

Hi All!!!!

Please help me!!!

I use LabView to read  and write  19 Temparture controls (WATLOWS) throught RS485 I use USB-8473 cable, but sometimes my system lose the comunication and lose data, some bady Know what can I do for fix this issue?

Thanks

[smercurio_fc]

The USB-8473 is not a cable but a USB<-->CAN interface. No RS-485. Are you sure that's the right part number?

[Kaliman]

I sorry I m Wrong, Use the NI USB-485.

Thanks

[smercurio_fc]

OK, that makes more sense. You haven't really provided any details. What's "sometimes"? Is it after a certain amount of time? Is it after you do something specific? What happens when you "lose communication"? Do you get an error? If so, what is it? Are you actually looking for errors (i.e., do you have ALL of the error clusters wired)? Have you tried reducing the polling rate? Have you tried with less sensors? Have you tried to monitor the communication?

[Kaliman]

Thanks, happen when I write any controller, I have 15 temperature control that read each second but I write when I change the setpoint but some time i Need change the setpoint anytime and when I did that I lose communication I check the Some Error in LabView but no display nothing

[TSJim]

Hi -

I assume you have all the devices on the same bus.  There could be a packet collision from the software.

Also from Wikipedia -

A bus without good pull up and pull down resistors will be noise-sensitive.

I had a problem once where someone wired earth ground between boards using RS485 and electric moters injected a bunch of noise into the bus.  Disconnect earth ground and let the boards float.

Thanks,
Jim

[TSJim]

I stumbled upon a good link for wiring RS485:

http://www.maxim-ic.com/app-notes/index.mvp/id/763

Thanks,
Jim