Guralp CMG-40T is a 3 axis seismometer with a flat velocity response of 800 V/(m/s) in the 0.03-50 Hz band. Doesn't need to be locked for transport and has a bubble level and leg screws for balancing.
Outputs are differential.
Needs a solid floor and a foam box in order to have good low frequency performance.
Home page: http://www.guralp.com/products/40T/
Datasheet: datasheet-cmg40t.pdf
Manual: manual-cmg40t.pdf
Breakout box circuit diagram:
Noise
We have yet to make high quality huddle test measurements of the self-noise of the Guralps. Here is there 'noise spec' plot:
At the 40M, we have serial # T4157 (which we got from Rich Mittleman at MIT).
Info from the calibration sheet:
zeros = 0, 0
poles = (-0.02365 +/- i*0.02365), -80, -160, -180
Response is the same for horizontal and vertical
Calibration sheet: calsheet.pdf
and we have serial # XXX (which we bought in July, '08)