modbus rs485

[JackPM]

Hi guys,

Im new to this  form.Im trying to get temperature readigs from P.I.D controllers via MODBUS rs 485.Im using RS 485 to RS 232 converter./can you guys please explain how to do that?

Best Regards,

Jack

[K C]

Hi,

First you have to be sure that you physical line (the RS-485) is OK. You can make a lot of mistakes there.

Tell us what converter you have, how things are connected at this moment and which ModBus device(s) you are using.

Kees

[JackPM]

Im using selec PID 500 to monitor temperature.I connect RS 485+ & RS 485- to the RS485 to RS232 converter (AC-RS485-RS232-01). I connect rs 232 port to com1.I tri  to get reading by using dasylab 11.0.But Im geting error message .

modbus ana00: 0: device error message: 4 address: 1

When im getting reading RX bulb is blinking.But TX bulb  is not blinking.

Why it is not working?

Thanks,

Jack.

[CJ_Butler__DASYLab_Pro]

Try it with DASYLab 13.... 

You can download the eval from www.dasylab.com

[JackPM]

Why Im getting that error messge?

[TomRizzo]

First of all,  did you put a 120 Ohm resistor from + to -?

Look in the manual of your device to make sure for the value but in any case, RS485 is a open collector technology so that, if the device does not have an internal one, this can happen.

Second, before you use DASYLab, you should try with a software that is provided by the manufacturer to make sure that your configuration is working correctly.   If yes than it should work on DASYLab as well.

Also, sometime the Modubus module is not working 100%, what we suggest is always to purchase an OPC server and then use the OPC module in DASYLab.  This is 100% tested and working great.

I also need to suggest to try with version 13 as CJ suggested

[CJ_Butler__DASYLab_Pro]

I'm not sure, but the Modbus module was newly rewritten for V11, and improved in V12 and V13.

Before spending time trying to diagnose the interface, it makes sense to try the most recent release of DASYLab, V13.

The evaluation version will let you determine if you're dealing with a bug in V11, or a configuration error.

Generally speaking, we provide active support for the current and previous release, V13 and V12. It's hard to continue to provide active support for older releases, especially when we know that improvements were made in the software in the last 5 years. V11 shipped in 2009, and V12 in 2011. V13 shipped in 2013. 

[JackPM]

ok.I will try it in dasylab 13.0 after putting a terminator.Thanks for the fast reply.

[K C]

Actually there should be a terminator resistor at both ends. Also a 0V connection could help.

Finally there are some manufacturers that reverse the + and - indication, try to reverse connect the A and the B line. I know it sound stupid, but some manufacturers do.

Kees

[erfan_sh]

Hi everyone

My project is controlling a furnace and im using DATAKOM DKM 409 that have modbus rs485 output. in this project i want to monitor the data by using labview.  due to do this i use a RS 485 to RS 232 converter but when i connect them to each other and to my pc there is no recognizing machine and when i want to use visa in LV it cant recohnie any connected device to it and give me below error:

LabVIEW:  (Hex 0xBFFF009E) VISA or a code library required by VISA could not be located or loaded.  This is usually due to a required driver not being installed on the system.

my converter is as this link:

http://www.securitycamera2000.com/products/CCTV-RS232-to-RS485-PTZ-Converter-For-DVR.html

please give me guide about what is wrong in my project. I really dont know why i can't config my visa port and my visa source is not recognized

thnks

Erfan Shahsavari