Instrument Control (GPIB, Serial, VISA, IVI)

[alphakokoro]

Hello,

I'm trying to control an EZ-Zone temp controller using LabView 2011

http://www.watlow.com/products/controllers/ez-zone-pm-controller.cfm?famid=14

Its communication protocol is Modbus RTU. It appeared that Watlow had a driver for it but it was written for 32-bit OS and standard bus so I cannot use it since my OS is 64-bit and use RS 232-to-USB cable.  After searching in this forum, I found out about NI Modbus library which I downloaded and tried it out.

First, I used the MB Serial Master Query Read Holding Registers.vi to read the current temperature. When I ran the VI with parameters set as Mode RTU, slave address 1, starting address 360, quantiy 2, I received timeout error code 6101. I tried to change the timeout duration but still received the same error code.  Has anyone used the NI Modbus library with success before or any suggestion regarding timeout error?

Attached is an example on how to assemble a Modbus packet for this controller.

Thank you

Tim

[Doug-B]

Hey LVNewbie85,

I was able to find this KnowledgeBase article that describes the timeout error you are getting:

http://digital.ni.com/public.nsf/allkb/628A4CF844B2382A862575D700349D99?OpenDocument

It looks like it is a hardware communication problem rather than a software issue.

Hope This Helps,

Doug B

[alphakokoro]

Doug,

Thanks for your reply. I am able to communicate with the instrument now but it keeps giving me random numbers output in Reading Holding Registers.VI from NI Modbus library.  I'm trying to find out where can I find the documentation for the NI Modbus library since it did not come with the zip file I downloaded from NI.

Thanks

Tim

[Doug-B]

Hey LVNewbie85,

Here is a link to a KnowledgeBase article that describes how to access the Modbus Library help files:

http://digital.ni.com/public.nsf/allkb/4E3BDFC165A8AA2886257722001C56CB

Also, there are examples in the LabVIEW Example Finder that are pretty well documented that might also be helpful.

Hope This Helps,

Doug B

[mtat76]

Hey Tim,

Did you ever resolve this?  We have someone over here who is trying to do something similar.

Matt

[alphakokoro]

Hey Matt,

Yes, I have resolved it.  Please let me know if I could be any help

Tim