USB to RS-485 Communication Problems

[MWJ]

I have a 778475-01, RS-485 to USB converter that is having communications issues. It is supposed to communication with a temperature sensor and update the temperaure @ 1Hz. It seems to be updating the temperature between 3 and 12 minutes. The old PCI base converter worked fine. 

The  settings for boh the old and new device are transciever mode: 2-wire auto, with the biad resistor checkbox unchekced

and 9600, None, 8, 1 and no flow control for the communication protocol.

Any ideas?

[David_Pratt]

Hey MWJ,

Where are the expected timing values of 1Hz being derived from?  Was this setup working at the desired rate previously and isn't anymore or was the code working at the described rate of 1Hz on a different COM port and now using the adapter slows it down?  Maybe this information will shed more light on the cause.

Thanks.

[MWJ]

DavidP,

I don't know about the expected timing values. All i know id that the PCI based RS-485 card worked fine and when I went to the USB version it does not work using the same communication settings. Since 1 Hz is such a slow communication rate for sending one decimal string of temperature I hope timing or speed is not an issue.

MWJ

[David_Pratt]

Hey,

I'm assuming that the transition from the PCI-485 to the USB-485 involved no change in the code other than the COMx being changed as the serial resource.  Is that correct?

If you could, please use NI Spy found in Start>>All Programs>>National Instruments>>NI Spy to see the duration of the calls being made. Attach that Spy file so we can see what's happening while your program runs.

Thanks,

[MWJ]

DavidP,

Yes, that's correct. The only thing that changed between the PCI and USB version is the Com port.

I ran the NI spy program but to no avail. It doesn't record any data.

MWJ

[David_Pratt]

Just to clarify, running NI Spy and clicking on the green arrow labeled "Start" shows no data whatsoever whenever you open and run your serial program? Even if you let it run for however long it takes for your serial program to get the data from the device?

[MWJ]

DavidP,

Yes, I clicked the green run arrow and ran and entire temperature sweep. The control program received 4 temperature updates over a 24 miniute period but nothing showed up in the NI Spy window.

MWJ

[David_Pratt]

What program are you using to read the serial data?  Is this a labview program making visa calls or is it something else?

[MWJ]

The program is called WinMix and I do not have access to the source code.I do not know how it is talking to the port or instrument.

I just know the vendor claims it works using either a NI PCI 485 converter baord or a NI 485 USB converter.

MWJ

[David_Pratt]

Hey,

Can you please provide any documentation or manufacturer website link for their support?  I'd like to see if there's any information that may explain the delay you're seeing.