Difference Between G and Grms

Hi,

I was referring to some of papers available on internet for HALT test guidelines. For Vibration tests, the paper says that chamber requirements should be -> Vibration output without load from 1 Grms to a minimum of 35 Grms.

But for test equipment, accelerometer range is +/- 500g.

I am confused what is the difference between g and Grms. How to select proper accelerometer?

Please help.

Thanks for your help in advance.

Regards,
Samir

(see Vibration and Shock Blog post for response to this)