VISA timeout error on periodical communications

[rolfk]

HiPot Tester! I hope your instrument has a VERY, and I really mean VERY, well isolated serial port. Otherwise your serial port communication is going to get messed up regularly. In the past I usually used a Serial to Glasfiber and Glasfiber to Serial converter to communicate with high voltage test devices. Anything else would always mess up the communication and usually the PC program as well. Preventing the transients from high voltage discharges to not travel through anything but optical connections is a very difficult thing.

[1984]

Just to provide a feedback / conclusion: the problem is clearly caused by some sort of a transient. We tried several things including shortening the cable length between the PC and the HIPOT, adding a USB hub to the line (hoped that it does some useful optical isolation), coil the the USB cable over a ferrite ring, but these didnt help.

What seemed to help (1250 execution without a USB crash while with the original setup it crashed in about 50 executions in average) is using the clip on ferrite filters on both ends of USB cable. (costs total of $4)

From the logs its clear that we still have a communication issue in about every 2-3% of the cases, but after couple retries the it recovers so it doesnt stop our app and we dont need to reboot the PC.

We didnt have a huge variety of products we could use for this test, so the results above might change.

[RTSLVU]

I had a similar issue with a surge generator. If we didn't use the very heavily shielded serial cable that came with it, the communications would fail every single time we triggered a surge.

[rolfk]

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@1984 wrote:

Just to provide a feedback / conclusion: the problem is clearly caused by some sort of a transient. We tried several things including shortening the cable length between the PC and the HIPOT, adding a USB hub to the line (hoped that it does some useful optical isolation).

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Unless the hub advertises optical isolation as one of its "hyper-super-high-end" features, you can safely assume that it does not have that.

And if it has that feature you can be sure that you can see it in the price tag. Such a device will cost at least in the higher end of 3 digit amount of US dollars if not more!

[Andrey_Dmitriev]

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@RTSLVU wrote:

I had a similar issue with a surge generator. If we didn't use the very heavily shielded serial cable that came with it, the communications would fail every single time we triggered a surge.

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It depends, many years we have had self made own X-Ray Generators (up to 450 kV), controlled by RS232 (novadays they network-connected with OPC UA) and was absolutely no problems, also with cables up to 30 meters long (without repeaters, but will not recommend). The problem was only with USB connections and FTDI chips (caused BSOD on Win10), but not from high voltage side, that was heavy motors emitting lot of electrical noise and that was eliminated with fiber optic - based adapters, they really helpful.

[RTSLVU]

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@rolfk wrote:

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@1984 wrote:

Just to provide a feedback / conclusion: the problem is clearly caused by some sort of a transient. We tried several things including shortening the cable length between the PC and the HIPOT, adding a USB hub to the line (hoped that it does some useful optical isolation).

---

Unless the hub advertises optical isolation as one of its "hyper-super-high-end" features, you can safely assume that it does not have that.

And if it has that feature you can be sure that you can see it in the price tag. Such a device will cost at least in the higher end of 3 digit amount of US dollars if not more!

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RS-232 to fiberoptic converters are not really that expensive. 

[rolfk]

RS-232 not, but the reference was about USB hubs. To get even USB-2 basic speed going you need fairly good opto-couplers. For RS-232 you can basically work with the cheapest optocouplers you find and still get 115kBaud. USB is a lot more demanding in speed as well as protocol complexity if you want to have a real passthrough hub.

[Andrey_Dmitriev]

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@rolfk wrote:

RS-232 not, but the reference was about USB hubs. To get even USB-2 basic speed going you need fairly good opto-couplers. For RS-232 you can basically work with the cheapest optocouplers you find and still get 115kBaud. USB is a lot more demanding in speed as well as protocol complexity if you want to have a real passthrough hub.

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For USB to Fiber we using these extensions

We haven't had any troubles so far (USB 3.1 was not tested as we don't have it on our devices).

Price is around 100-115€.

[rolfk]

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@Andrey_Dmitriev wrote:

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@rolfk wrote:

RS-232 not, but the reference was about USB hubs. To get even USB-2 basic speed going you need fairly good opto-couplers. For RS-232 you can basically work with the cheapest optocouplers you find and still get 115kBaud. USB is a lot more demanding in speed as well as protocol complexity if you want to have a real passthrough hub.

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For USB to Fiber we using these extensions

We haven't had any troubles so far (USB 3.1 was not tested as we don't have it on our devices).

Price is around 100-115€.

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Thanks! Good to know they exist. It’s been a few years I was researching that and there seem to be more reasonable options nowadays. Not a hub actually but in this case even better for connecting high voltage surge devices.