Set RS485 to 2-wire mode on cFP-2220

[RavensFan]

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B-man wrote:

Oops, I was messing arround with the property node, must have deleted the constant for wire mode. See attachment again. It's in the MB Init under "instr" last node "serial settings: wire mode.

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No.  It's not there. Because you didn't attach MB Init, and you used the standard name, the file loads with the MB Init from my Modbus library.

As I said in post #14, if you modify it, make sure you rename it.  Think about what will happen if you upgrade LabVIEW.  You'll reinstall the MB libaries with the new version.  Then when you go to load your old VI's it will find the new version of MB Init and you will have lost the changes to your special MB Init you made.  Make a new MB Init, rename it, and save it with the rest of your project files.  Then it won't get lost or cross-linked with the original MB Init.

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B-man wrote:

Besides the com+, com-, and ground wires, do you know if I need to connect V+ (voltage) wire to the 10pin RS485 jack to make the signal differential, maybe? If so, which pin would it be? The serial quick reference guide does not specify. Currently I have it connected to pin 1 (a "no connect" pin).

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I think you should connect the voltage and ground wires to a powe source.  Per page 6 (and you or someone even has it highlighted in yellow).  It doens't look like these sensors have any other way of powering their internal electronics.

Message Edited by Ravens Fan on 03-13-2009 09:23 AM

[B-man]

Hi All,

Looks like I might be at the end of the road. Now I know why NI fieldpoint does not support 2-wire mode. It's because my sensors are too quick to repond to the RS485 port. The port can't switch from TX command to receive RX command fast enough. I did get some correct data, but the extra data and polling gets stuck. I am going to try to change the baud rate on my sensors to try to slow it down, but I doubt it's goiing to work. On to plan B perhaps convert 2-wire to other serial or 4-wire, externally.

Thanks for all the guidance!!!

B-man

[Mads]

That's too bad, B-man. I wish NI could speed up the switching time, then they could fully support both 2 and 4-wire.

We always use 2-wire, and adding an extra componant to the system just to go from 4 to 2 wires is not an economic solution. We make the sensors ourselves though  so we are fortunate enough to be able to fix the problem by adding a delay to the response.