Calculation of maximum FPS rate with an external trigger

Answered

goekce erguen

• June 15, 2023 21:09

Hello,

I have a question regarding the maximum FPS (frames per second) rate and read-out time for the Grasshopper3 USB3 cameras [GS3-U3-32S4]. We are using 4 cameras and would like to optimize their performance with different exposure times.

Could you please provide the following information:

1. What is the maximum achievable FPS rate with an external trigger, considering the read-out time?
2. What is the read-out time for capturing images at the highest resolution?
3. Are there any additional factors or limitations to consider for determining the maximum achievable FPS rate?

Thank you for your assistance!

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• Official comment

  

  TDY_Manuel

  Community team

  • June 20, 2023 13:27

  

  Hi Gokce, 
  
  Yes, setting "Trigger Overlap" to "read-out" equals trigger mode 14.
  I doubt that you will see any problems when you use this feature. While we do not give a number, the jitter in start of exposure is very small and I have not heard of any customer complaining about it. 
  
  Does the software you use allow you to read chunk data from an image? That is where you can get the timestamp representing the end of exposure. 
  Once you have access to the image you can immediately execute the Timestamp Latch node on the camera and then read the latched time from the Timestamp node. 
  Then you can compare both values. 
  
  You can also use the chunk data timestamps of the images to verify the accuracy of the camera frame rate with overlapped trigger enabled. 
  
  Best regards,

  Manuel 
• 

  TDY_Manuel

  Community team

  • June 16, 2023 12:46

  

  Hello Goekce, 

  These numbers are not specified but you should get very close to full frame rate when you use trigger mode 14 (FlyCapture2) or overlapped trigger (Spinnaker). 

  If you have the camera with you, you can test this by slowly increasing the trigger rate. Once you hit the limit, the frame rate will drop to half the previous rate. 

  I would expect the image readout and transfer to the PC take ~10ms. If you need more exact numbers you can use the embedded timestamp (FlyCapture2) or chunk data timestamp (Spinnaker) and compare it to the time when the image is received on the PC. Please let me know if you need help with that. 

  Are you asking out of interest or do you see any problems? If the maximum triggered frame rate is much lower than 120 fps with default settings, please try lowering the exposure time. 

  Best regards,

  Manuel 

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• 

  goekce erguen

  • June 20, 2023 06:16

  Hi Manuel, 

  Thanks for your reply. To be able to capture Webcams as well, we are currently using 2ndLook. There is a "Trigger Overlap" parameter that can be set as either "off" or "read-out". I guess this may be Mode 14 in 2ndLook software. 

  However, after we read about Mode 14 in the documentation (https://www.manualslib.com/manual/1790613/Flir-Grasshopper-3-Series.html?page=59&term=Mode+14&selected=1#manual), we decided not to use Mode 14, since it does not ensures the precise exposure start. 

  thanks for your suggestion about to figure out extract readout time. I have a follow-up question. Is the timestamp attached to the frames embedded timestamps? If so, where/how can I get the time when the image is received on the PC. 

  I asked about it because we realized that we cannot get the full frame rate (as you explained, once hit the limit, the frame rate drops) and were interested in calculating the highest possible frame rate for a given exposure time and frame resolution. 

  Best, 

  Gokce

   

   

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