Modbus RTU. Error 6101 occurs by reading from PID controller

[MelanieE]

Hi,

could you please post the code you are using currently? I would like to take a look into it.

Best,

Melanie

[stiefel92]

Hi 

The document doesn`t help unfortunately. 

I am attaching the code which I am using but it hasn't changed a lot since my first post. 

Thanks

Lukas

[pep91]

Hi stiefel,

try to initialize the boolean value you are passing to the function MB Serial Master Query Read.

Maybe this might generate the timeout error.

Kind regards,

Pep

[Dave_Brandt]

Try reading Holding registers instead of input registers.. Also use a bundle by name for your cluster.

[stiefel92]

Hi 

Thank you for your help. I rebuilt the program as Dave has mentioned and still get the

error -1073807298 ocurred at VISA Read in MB Serial Receive.vi:3-> MB Serial Master Query.vi:2->PID-Read.vi

Possible reasons:

Visa: (Hex 0xBFFF003E) Coud not perform operation because of I/O error. 

I get this same error using the set_temperature.vi and it still sets the temperature correctly. The controller also shows a little light indicating communication over the interface when running any of the programms.

So the same error as before which I have mentionend in Message 9. Any suggestions how to resolve that problem? 

Regards 

Lukas 

[Dave_Brandt]

Have you tried increasing the timeout value? What is it set at? Also is your address the same for unit ID in the controller? You can by sending a broadcast "Unit 0" and all will except the values for setpoints (Writes) but if you request data from a controller and it does not have the same ID it will not respond.  The slave Address must be the same as what is set in your controller. 

[stiefel92]

The timeout value is set to 10000 and I have tried increasing it but it doesn't make a difference. Anyway I am not getting a timeout error right now. 
The slave address of the controller is set to 2. When I am using the programm "Simply Modbus Master" communication works fine.

Thanks for your efforts. 

[Dave_Brandt]

If you can use a different controller Automation direct has a good selection. I use Automation Direct Solo temperature controllers with the same NI modbus library and it works very well.  Automation direct makes a modbus serial to modbus Ethernet gateway. It works very well. This eliminates a lot of the serial port problems with converters and also allows for setting up polling of slaves in the gateway.