Re: Investigating possible effects of EMI on FireWire cameras

[Alex J. <al...@nu...>]

> On 9 Jun, 2014, at 18:41, Stefan Richter <st...@s5...> wrote:
> 
>> On Jun 07 Damien Douxchamps wrote:
>>> On Sat, 2014-06-07 at 13:50 +0800, Alex John wrote:
>>> I am using a pair of FireWire cameras (Guppy/Guppy Pro) connected via
>>> an AVT pci controller card (TI-TSB43AB22A). I'm using them as vision
>>> cameras for an underwater autonomous vehicle. I'm facing a very weird
>>> issue where the cameras shut down when certain thrusters are fired.
>>> The device disappears from the device list and has to be physically
>>> replugged to raise it again.
>> 
>> That looks like a power supply issue to me... At least I would start
>> investigating there with a multimeter to see if/how the voltage drops on
>> the supply rails when the motors run. If you use batteries or an
>> umbilical (any other option anyway? :) you may get voltage drops due to
>> batteries limitations or wire resistance.
>> 

We already filter the power to a certain degree and the wire resistance was measures and found to be okayish. I can get the exact measurements but this brings me to the issue that I forgot to mention which I'll detail below-

>> Next step is using a scope to check the noise on the supply voltage, if
>> the motors run on the same supply as the cameras.
> [...]
> 
> I too think that this sounds more like instability or noise on the power
> supply rails rather than HF noise on the signal lines.
> 
> Incidentally, I too have got a "device disappears" problem at home with a
> cable TV box (FireDTV C/CI):  Often when another electrical device is
> switched on (or sometimes when switched off) at the 230 V 50 Hz power
> grid --- e.g. a PC, monitor, RAID enclosure, or vacuum cleaner ---, the bus
> with the FireDTV sees a bus reset, and the phy of the FireDTV is no longer
> present according to selfID reception.  To recover, the FireDTV has to be
> plugged out and in again.
> 
> The FireDTV has a TSB41AB2 phy according to lsfirewirephy from jujuutils.
> I have got some other devices with TSB41AB2 phy though which do not
> exhibit such an issue.
> 
> Usually I power the FireDTV from one or another PC's FireWire bus power.
> The PCs don't exhibit any other stability issues though, neither do any of
> a bunch of other bus-powered FireWire devices of various kinds.  The PCs'
> PSUs (Seasonic models from different generations) are said to deliver
> comparatively clean and stable output.
> 
> From a few brief tests it seems there are two ways to fix this issue:
>  - Powering the FireDtV from a separate 12 V PSU, or
>  - putting a ground loop filter (a capacitive coupler, I think) between
>    TV cable and FireDTV.
> 
> So I suspect that my particular issue is not actually caused by a voltage
> drop on the FireWire bus on its own but by a current between FireWire
> ground and TV cable ground.

Thanks for the suggestions, I'll look into it but there's another aspect of the problem that I forgot to mention.

The cameras that die are always the external cameras. The difference is that we have cut the cables and used our own underwater cables including connectors. The camera that is in the hull connected straight using the original FireWire cable never has any issues. Both cameras are running on the same power system. 

> -- 
> Stefan Richter
> -=====-====- -==- -=--=
> http://arcgraph.de/sr/

Thanks
Alex