Who's the expert on USB to serial adapters?

I've searched this a few ways, and found a lot of older info - but not much that was recent (this decade). So far none of the info has helped. I also read through the extensive troubleshooting faq on th host engineering site which had turned up on here searching, but no progress.

Here's what I have:
Dell precision M4400 laptop with XP pro and DS5
Direct logic 205 with 240 CPU and ctrio high speed counter
4 different USB to serial adapter cables (using prolific driver)

I can connect to the Plc an have transferred programs. Can sometimes get into ctrio workbench. The problem is I get a comm failure within a few minutes of connecting, and this locks up direct soft, to the point of having to reboot. I have even seen blue screen of death a few times! I am not getting any errors in the hardware manager.

I used same adapters on a laptop with windows 7 and have exact same results. If I go to 2 different desktops with real serial ports it functions just fine...

I work at a technical college that has Plc classes and they use th exact same adapter cable (group buy and I got one from them). So far they just say m computer has a config problem, but I'm not sure I agree.

Any suggestions??

Thank you!

get a keyspan usb to serial and your problems will be gone!

http://www.google.com/products/cata...a=X&ei=6PJCT73qE5Pbgge6x5W8CQ&ved=0CD4Q8wIwAA

I cannot speak for the hardware that you are connecting to, but I have had success with the Keyspan USA-19HS (comes highly recommended around here) and I have recently started using this industrial one. Both can be found here:

http://www.ind-concepts.com/CommunicationData.htm

Just a guess; you might have a ground loop between the PC and the supply circuits of the logic controller.

Try putting the PC on a nonconductive surface and running it on batteries only to see if the behavior changes. You can try measuring with a voltmeter from the USB shell to the ground of the PLC as well.

I worked on a motion controller a few months ago that put out so much noise we couldn't use a USB mouse when connected to it over RS-232.

The ground loop might be on to something. The weird thing is it seemed to get worse today and I was using it in a different location...

Of course running the laptop on its battery would definitely solve the problem - the batt would die before the connection for certain. I need at new one!

Thanks for the responses guys!

I use a B&B unit, on Windows 7 host, using VMWare guests, and have never had a problem with it.
Except, of course, when I was trying to make it (The USB device) share to a W3.1 guest...like that would ever work.
Anyway, B&B is worth a look, too.

I use this one http://www.serialcomm.com/USB_adapters/usb_to_rs232_rs485_rs422_adapters.aspx

The USB-232-2 has never failed me, also I really like the driver software, you can set the comm port, and it will stay the same no matter which USB port you plug it into, a feature many others lack.

http://www.serialcomm.com/USB_adapters/usb_to_rs232_rs485_rs422_adapters.aspx

Vey interesting - the serialcomm.com one uses the FTDI chip. This is the exact same chip that the Omron USB/serial adaptor uses. I use the Omron one - it has been tested by Omron on all their PLCs and comes guaranteed to work with Omrom PLCs. I have never had a problem with it to any device.
The other adaptor I use regularly is the Adam-4561 from Advantech. It is a bit bulky but is fully isolated and has a terminal block where you can wire out for USB/RS232, USB/RS422 or USB/RS485.
I carry this device and some pre-wired terminal blocks (spare blocks bought from RS) to open ended and 9 pin connections for the devices I normally use.
I see they have a new one with ESD surge protection built in also.
The Adam has never failed me either. It may be the one for you due to the isolation built in to the adaptor.
I have also used the Adam device from a computer to PLCs utilising the RS422 connection back into Citect SCADA. Have Citect running and my PLC software at the same time. Bit slow of course as it is RS422 @19200 baud but it worked without fail.

You didn't mention what the model numbers of any of the USB to Serial adapters are. As Ken said it could be a ground loop problem, but this shouldn't blue screen the PLC.

Please list the model and part number of the adapters and I can provide more information on what to do to troubleshoot the issue.

Here is a link to one of the cables:
http://www.cablestogo.com/product.asp?cat_id=101&sku=26886

The other ones I do not have a clue on, one of them seems to use the same driver, and another is totally different. I do remember seeing ftdi in one of the driver installs I think.
The problem seems to have gotten worse - I now cannot seem to connect at all. I have a friend brining his Dell port replicator which includes a true serial port to see if that works better. If it does I can pick one up for about $25 used and eliminate the adapters.

The main issue with USB to Serial convertors is that the wrong driver gets installed by Windows. Not all drivers are created equal. Windows will go grab the one that it best thinks suits the device ID. If the devices happen to have a similar chipset Windows will sometimes grab the wrong driver.

Your best bet is to see what the chipset or maker is for one of the cables, go get the driver from the chipset manufacturer or makers website, uninstall all drivers, reboot, install just the driver for the one cable and reboot again. Be sure to point Windows to the correct driver instead of letting it "Search" for it.

Be aware that some drivers install themselves as programs, so be sure to check the Add/Remove Programs section of the Windows Control Panel to see if any have hidden themselves away there.

dmroeder, thank you for the plug...

Tubularfab, We sell a USB version of the D2-DSCBL and others, you can find it on the page below, we have sold a lot of them and have had very few issues, like Icky said the drivers are a big issue, our newest USB cable have the drivers built in most Windows 7 builds... so they are just plug and play

http://www.ind-concepts.com/AD_Mitsubishi_Omron_PLC_Cables.htm