SRS primary positive and negative

[floattuber]

I'm having a hard time wrapping my head around the concept of a primary positive and negative SRS responses. What is physically happening to produce these waveforms? How are they derived?

 

[Transient1]

My understanding is that the positive SRS response is the acceleration response in the direction of the shock and the negative shock is the 'returning' acceleration. The reason that the measured positive response is not equal to the negative response is because of damping in the system.

The object is vibrating, that produces the waveform. By measuring acceleration versus time the SRS can be derived. The shock response spectrum (acceleration versus frequency) is derived from the fourier transform of acceleration versus time data. Fourier transforms are the means to go from the time to frequency domains.

Hope that helps.

 

[jimkinney]

A difference between them is an indication of problems, such as saturation or DC shift.

Jim Kinney
Kennedy Space Center, FL

 

[Transient1]

Jim,

Can you elaborate on that further? Are you talking about the effect of the shock on the accelerometer?

 

[jimkinney]

Transient1,

I should have said accelerometer problems. Both of these problems add low frequency energy to the wave form, and will show up with the velocity shifting (DC) or continuing to increase as the transient dies out. High pass filtering (5-10Hz) will sometimes get rid of the DC offset. The continuous change in velocity will require some kind of trend removal (wavelets work quite well), and may also remove some parts of the waveform that you really need. As such, manipulating the data is a last resort if you can't retest (ie. flight data reduction).

Jim Kinney
Kennedy Space Center, FL

 

[floattuber]

Ok, I thought the +- was more complicated than that.

I've been told a good rule of thumb is that a difference of 3dB between the + and the - was acceptable. Does this sound about right?

 

[jimkinney]

That seems reasonable to me.

Jim Kinney
Kennedy Space Center, FL