Omega CN7500 communication (ASCII protocol)

[mroy17]

So if I get this converter, I can then use the DAQ board? Or will I have to use a different kind of connection entirely?

Thanks for the response!

[mroy17]

I guess a better question would be: How did you connect your PC running labview to your Omega controler? Directly through the serial port on your computer? And the only thing between them is the converter you mentioned? 

Sorry, I'm just a bit new to the digital communications, I have only worked with analog inputs/outputs through a DAQ board.

Thanks again!

[CWT]

Hey no problem.  You will not need the DAQ to communicate with the controller.  You are definitely on the right track speaking of the serial port though.  How you want to wire the device is up to you, but what I do with mine is get a soldercup style DB-9 female connector, solder wires to the correct pins on the connector, and then connect the wires to the RS485 pins on the controller.  From the DB-9 female connector, I run a standard serial cable back to my pc.  I connect the serial cable to the RS485 to RS232 converter and then connect the converter directly to the COM1 port (or other available ports) of my pc.

After you have the controller connected to your pc, you will need to set up the serial configuration settings on the controller.  You can see how to do this from the device's user manual.  Basically, you go into the controller's menu (physically pressing the buttons on the front of the controller) and set the controller address, baud rate, parity, etc.  The main thing to remember is that you need to set the controller's settings to match the program's settings (baud rate, parity, etc.) or else the program will not communicate with the device properly.

I typically use the following settings:

Baud Rate - 9600

Flow Control - None

Parity - None

Data Bits - 8

Stop Bits - 1

Once all you have the device configured properly, run the example program and make sure you are sending the correct address, and you should be able to communicate right away sending set points and reading back the process value.

Hopefully this explanation makes sense.  If not, let me know and I will try to help get you set up and running soon.

[mroy17]

Thanks so much, that definitely clears up a lot. The laptop I have to work on does not have any COM or serial ports so I am going to buy a serial to USB adaptor. Once I do that, how do I then identify that USB port to the program?

[CWT]

Using a Serial to USB works well too.  Once you download the driver for the adapter, Windows will install the device and notify you that it was installed properly and is ready to use.  Once you get this message, go into the Device Manager (Start -> Control Panel -> Device Manger) and expand the Ports (COM & LPT) section to see the COM port that was allocated to your adapter.  The adapter will most likely be labeled something like a Prolific Serial-to-USB adapter (COM7) for example.  Once you have this allocation, select this COM port in the LabVIEW program.

You could go with something like this to go straight from RS485 to USB as well. It will simplify your setup from having to use multiple converters to go from RS485 to RS232 to USB, plus it has built in isolation.

http://www.bb-elec.com/Products/USB-Connectivity/USB-to-Serial-Adapters/In-line-USB-to-Serial-Conver...

Hope this helps.  If you have any more questions, please let me know.

[mroy17]

Just out of curiosity, why is the converter needed? Can't labview communicate in RS-485?

[CWT]

The converter is needed for incompatibility with your hardware, not LabVIEW.  If your pc has an RS485 port, then you would not need a converter.  For instance, most generic desktop pc's will have an RS232 (COM1) port that comes standard.  If you try to connect the RS485 directly to the RS232 port, it will not work.  Since you are using a laptop with USB ports only, you will need the converter to go from RS485 to USB.  Once the hardware is compatible, LabVIEW will be able to communicate with the serial protocol.

I realize the converter costs more than the temperature controller itself.  There are other options out there that will perform the same function for less cost.  I've always had very good experiences with the B&B Electronics hardware, plus I like to get isolation whenever I can.

If you have more questions on the differences between the RS232, RS485, and USB hardware interfaces, you might try doing an online search or waiting for someone else who is much more knowledgeable than me on the topic to reply.

Hopefully this is helpful. If not, I apologize.

[mroy17]

It has been very helpful! Thank you so much!

I'm going to get these parts ordered and I feel confident I'll be able to go from there.

Thanks

[CWT]

Good deal!  I'm currently using the CN7933 on multiple projects at the moment, so if you have any questions with the code or need any further help setting up your program, let me know.  These really are some nice controllers for the cost and they are easy to use.  No doubt we can get you up and running in no time.

[dextor1]

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@CWT wrote:

Hey no problem.  You will not need the DAQ to communicate with the controller.  You are definitely on the right track speaking of the serial port though.  How you want to wire the device is up to you, but what I do with mine is get a soldercup style DB-9 female connector, solder wires to the correct pins on the connector, and then connect the wires to the RS485 pins on the controller.  From the DB-9 female connector, I run a standard serial cable back to my pc.  I connect the serial cable to the RS485 to RS232 converter and then connect the converter directly to the COM1 port (or other available ports) of my pc.

After you have the controller connected to your pc, you will need to set up the serial configuration settings on the controller.  You can see how to do this from the device's user manual.  Basically, you go into the controller's menu (physically pressing the buttons on the front of the controller) and set the controller address, baud rate, parity, etc.  The main thing to remember is that you need to set the controller's settings to match the program's settings (baud rate, parity, etc.) or else the program will not communicate with the device properly.

I typically use the following settings:

Baud Rate - 9600

Flow Control - None

Parity - None

Data Bits - 8

Stop Bits - 1

Once all you have the device configured properly, run the example program and make sure you are sending the correct address, and you should be able to communicate right away sending set points and reading back the process value.

Hopefully this explanation makes sense.  If not, let me know and I will try to help get you set up and running soon.

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Hello there,

Thanks so much for your detailed instructions how to wire and setting up the CN7500 controller. I followed everything you mentioned and tried both COM1 and USB convertor (allocated at COM3) connections, and set both the port and controller settings exactly the same you showed here. The problem I have is that I am not able to select either COM1 or COM3 visa source in the LV programe, I mean it seems the CN7500 controller is not recognized by LV.

Anything I am doing wrong, or additional steps I need to do? Do I need something like nimodbus? I am using LV2012 and can not find any competible version of nimodbus for LV2012.

Any suggestion will be greatly appreciated.