RS232 to RS485 converter unable to communicate with a device

[FRainey]

Hello.  I am using the GILSON 508 Interface (converts RS232 signaling to RS485) to communication with a Gilson Minipuls3 pump.  I have designed a program in LabVIEW, but I am unable to get any response from my instrument.  I have configured the serial port according to instrument specs.  I am sending the nonprinting ASCII control characters by entering the HEX equivalent (in Hex Display Mode).  I have also tested the 508 Interface to insure that it is functioning (connected the Master and Slave Lines).  Can anyone give me any suggestions on how to go about fixing this problem?

[Chad B]

There are a few things you could try.  First, open the "Basic Serial Write and Read" VI from the Example Finder.  This example does just what it says--writes and reads to a serial port in the most basic way possible.  You'll need to add the termination character in the input box, as it's not configured by default.

If that doesn't work, try communicating directly with the port in HyperTerminal.  If there's a basic connectivity problem, you'll be able to tell by using HyperTerminal.

[savingHope]

Me: I am quite new to this field and I do believe i need to learn alot, but in the meanwhile I facing troubles to solve a problem.

To Do: Controling Gilson miniplus3 peristaltic pump using LabView2014 for experimental purposes.

Haves: Installed LabView 2014 on Windows 7, Gilson pump directly connected to computer using RS323 cable, who's one end is connected to GSIOC and other end to computer via GPIB-USB.

Questions: Will this arrangement work without adaptor/system interface?

If it is so what else I do exaclty need in terms of drivers?

What would be the good starting point in this regard?

Actually I have been googling since more than one week and have been unable to get any proper effective way to grab this scenario. Any piece of advice will be of great help.

[Dennis_Knutson]

You can't physically connect an RS232 cable to a USB-GPIB so what you are saying does not make any sense. If your instrument is RS232, then anything related to GPIB doors not make any sense.

[savingHope]

Following picture depicts the instrument and the connecting cable with converter which I am trying to use in this setup. I think previously, I have used wrong nomenclature for these components and that why I prefer to attach the corresponding pic.

Will this arrangement work or not?

[Dennis_Knutson]

Possibly. The first thing to do is to install the Windows driver for the USB-Serial converter. This should show up in Device Manager as a com port. Then you need to install NI-VISA (http://www.ni.com/download/ni-visa-15.0.1/5693/en/). This will also install Measurement and Automation Explorer (MAX). The com port has to be visible there. You should test communication in MAX or with a program such as Putty. You use the instrument's manual to match the pc's com settings (baud rate, parity, etc) to what the instrument is set to. The manual will explain what commands you need to use to write/read the instrument. You'll need to check if the cable type is correct. There are two basic types. A straight through or null modem. The manual should explain what type you need. You can use an ohmmeter to check. Once you have established communication and are familiar with the command, then you can start with the serial examples that come with LabVIEW.

[johnsold]

The image you posted refers to RS-422 and RS-485, not RS-232.  I think those protocols are differential while RS-232 is not. Perhaps some RS-422 interfaces will work with an RS-232 cable, but it is certainly not optimum and definitely not guaranteed to work. 

Look for an RS-422 to USB converter. Black Box makes a wide variety of converters.

Lynn

[Dennis_Knutson]

Good catch. I didn't notice that label on the image. A USB-RS232 converter will certainly not work.