Deflection is always measured away from the indicator as shown by the arrow in the video and my schematic on the attached excel sheet.  Since the meter is mounted on the outer ss tube the negative measurements indicate that the end of inner tube is moving closer to the end of the outer tube and thus the coil itself must be expanding while the deflect-o-meter is contracting.   

 

Also, I went back and looked at the end values for the gage after the shot had passed and compared them to the initial.  In all but two runs they are not the same.   The average difference for the 36 kamp cases is around .0007 in. 

This appears to be close to how the meter was behaving on the dummy tests at ORNL as readings would vary by .0005 where the meter did not return exactly to its starting value when pinged with a quick vibratory type force (hammer).  When a nice easy slow force (hand) was applied the meter would come within .0001-.0002 in of its original setting.   Also, the backing measuring plate, if rotated slightly, as in vibration settings, would also account for some error since it did not have a machined flatness to it at all.

 

Kevin

 

 

 

Does a negative deflection reading mean that the deflectometer is extending or contracting?