Acquisitio​n.GetLastI​mage based on Gige camera external trigger doesn't give me the latest image

Question

I am planning on using the camera's trigger input to start capturing the image. I have 4 cameras, but I only need 1 image each time. \
Here are the steps I am using:
1.  Set the camera to exteral trigger
2. PLC send the trigger to camera to take the picture
3. Read the image from camera.
It only works for the first time becasue it can get the first image, then never refresh the image again..
Here are the sample codes I use:
                     _session = New ImaqdxSession("Name")
                    _session.Acquisition.Configure(ImaqdxAcquisitionTy​pe.SingleShot, 1)
                    _session.Acquisition.Start();
                    _session.Acquisition.GetImageAt(_currImage, 0)
The piece of code is running when the PLC sends the trigger to camera. I was wondering whether it might be caused by no image was taken at that time.
I also tried
               _session.Acquisition.GetLastImage(_currImage)
Same behavior..
The strange thing is if I change the codes like the following
                    _session = New ImaqdxSession("Name")
                    _session.Acquisition.Configure(ImaqdxAcquisitionTy​pe.Continuous, 1)
                    _session.Acquisition.Start();
                    _session.Acquisition.GetLastImage(_currImage)
It only works when 2 trigger sent from PLC. Should I use _session.Acquisition.GetNextImage(_currImage) instead?
Question:
How I do know the new image is arrived?               

Answer 1

How are you running the repeat acquisition? I assume you are running it a loop of some sort. Are you closing the IMAQdx session at any point? This will help understand why we are seeing the behavior you are getting.
Cameron T
Applications Engineer
National Instruments