How to do a simultaneous snap from two GigE cameras?
I have 2 Basler Scout 780-54gm cameras (monochrome GigE) that I am triggering externally at 10 Hz. This frame rate is modest and the resulting data rate is not particularly high. I would like to get images from both cameras from the same trigger pulse. I have an Intel Pro/1000 NIC and I am using the NI driver that shows up as National Instruments GigE Vision Adapter. When I use the Basler Pylon Viewer (the software that comes with the cameras) I can see perfect images from both cameras at the same time at 10 Hz. This tells me that the network, NIC and drivers can handle the data rate with no problem. I have jumbo frames enabled.
When I try to acquire images into LabVIEW 8.6 with IMAQdx vis, though, I run into problems. I can acquire from each camera alone, but I can't get both at the same time cleanly. The images are shot through with black horizontal lines that appear and move erratically. I have attached a vi that shows the problem. I configure and start both acquisitions, then enter a while loop which reads the images. If I do the acquisitions sequentially by starting and stopping them inside the loop and making sure that one stops before the other starts then I get high-quality images but they are not from the same trigger pulses, and the overhead of starting and stopping the acuisitions slows things down so that I can't get images from every trigger.
My guess is that this is a problem with the way LabVIEW is managing memory, resulting in corruption with simultaneous acquisitions. Are there any settings I can change to cure this problem? I have experimented with everything that I know about, but no success yet.
Attachments:
Two GigE Grabs standalone.vi 50 KB
Hi Richard:
You should put the tick count function in a sequence structure in order to make the loop timing consistent each iteration, but what are you receiving as a loop time? If it's operating in less than 100ms, it shouldn't be the software that's affecting the images.
One other thing you can try is to get rid of the error wire between your Get Image VIs. This will keep the program from forcing a delay by executing the functions one at a time.
Alex Person
NI-RIO Product Support Engineer
National Instruments
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