Time delay

Supporting Labview 2012 and up
goncinious1
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Time delay

Postby goncinious1 » Fri Mar 20, 2015 10:40 am

Hi all,

So, I am building an horizontal ladder coupled with force sensors (44 load sensors) to study locomotion on mice. While the mice walk through the corridor I am using a high speed camera to record a movie (400 fps) simultaneously.
The problem that I am having has to do with the synchronization between the image acquisition timestamp and the load sensors acquisition timestamp. I am having a time delay of ~20 ms between the two (the timestamp corresponding to the increasing intensity of the sensor is delayed relative to the the timestamp corresponding to the frame where I can see that I am starting to do pressure in the sensor).

First I thought that this could be happening because I have 44 sensors connected to a USB hub and then connected to the computer. So I tried with only one sensor connected directly to the USB port and I still have the same delay.

Now I am thinking that the delay could be explained by the USB cable itself. The timestamp that I am saving corresponds to the time when the value measured arrives to the computer and not to the when it was actually read. Could this explain the problem?
What do you guys think might be the origin of this problem? And how could I fix this?

Specs of my setup:

Programming in Labview 2012
Load sensor is acquiring at 10 ms
Camera is acquiring at ~2.5 ms
The timestamp that I am saving corresponds to the labview clock tick and it is the same for the sensors and the camera.
PhidgetBridge 4-Input interface
Micro Load Cell (0-100g)

Windows 8.1 pro
i7 CPU; 3.60GHz
64bit based processor
USB directly in the computer USB port (using USB cable provided)
This computer is used only for this acquisition. It is not even connected to the internet.

Also I attached some pictures of my labview vi and some matlab plots trying to explain the problem.

[img][img]http://s27.postimg.org/b225y95wz/phidget_vi.png[/img]
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[img][img]http://s1.postimg.org/aen6km6m7/delay.png[/img]
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[img][img]http://s28.postimg.org/nzi86rs7x/delay_zoomin.png[/img]
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