PDA

View Full Version : Missing trigger from DMM-22BUC03



JoaoPV
May 19, 2014, 20:38:03
Hello,

I have a project with a DMM-22BUC03 and a DMM-22BUC03ML, in trigger mode acquisition using two independent trigger sensors. Every once and a while one of the cameras does not acquire a new image, although its trigger sensor outputs the correct signal.

I am using the USB driver ver 2.4.14on Windows XP Pro with SP3.

During my latest testing, this issue is more frequent when the two cameras trigger almost simultaneous. I have not experienced this issue, thus far, when they trigger far apart.

Any ideas?

Thanks,
Joao

Stefan Geissler
May 20, 2014, 08:59:44
Hello

If the cameras are connected to the same USB controller, you must lower the frame rates of the camera. Otherwise they will create and send the image to fast and the USB bandwidth is exhausted.

Please keep in mind, the cameras have no memory, therefore, the image data must be sent as soon as they are read from the sensor.

JoaoPV
May 21, 2014, 12:56:55
Hello Stefan,

Thank you for your reply. Both cameras are set for 30 FPS and only transfer the image when they are triggered. Considering these cameras have 744x480 a monochorme image translates in approximately 360k bytes per image transfered. The two cameras, if triggered simultaneously, would transfer 2x360k on the same USB controller. The 720K is still under the 35MB/s limit of a USB 2.0 controller.

Is this analisys correct?

If so, what could cause one of the missing image from one of the cameras?

I look forward for your reply.

Regards,
Joao

Stefan Geissler
May 21, 2014, 14:54:27
Above, I wrote


Please keep in mind, the cameras have no memory, therefore, the image data must be sent as soon as they are read from the sensor.

That means, the image data must be transferred immediately. If both cameras are triggered at the same time, then there is not enough bandwidth on USB availalbe, if both cameras run with maximum speed. You create a burst of USB traffic.

JoaoPV
May 22, 2014, 13:59:07
Stefan,

I understood your original comment on the immediate data transfer.

But if two 744x480 mono cameras, triggering at the same time, transfer 2 * 744 * 480 bytes = 714,240 bytes, how will this exceeds the USB 2.0 bandwidth?

Stefan Geissler
June 4, 2014, 09:58:15
You did not understand. The USB bandwidth allocation is not determined by the amount of data. It is determined by the amount of data per second. If both cameras are set to full frame rate, then there is not enough bandwidth on the USB bus to handle the burst of data to be transfered.