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Fri Mar 21 23:15:11 2008
Ranger SS-1: New Setup
The Ranger seismometer has been in a bad state. Its output had been sent into a SR560 without any termination.
The seismometer is, internally, just a mass on a flexure with a magnet and a pickup coil for readout.
The damping of the system depends on the resistor hooked up across the coil. With the SR560 this is
the 1 Meg input impedance of it and so the mass is undamped.
installed a 4300 Ohm resistor in there
which seems to nearly critically damp it. However, this will not
allow us to reach the ultimate quantum noise limited performance. We will have to analyze the thermal, voltage,
and current noise to get that.
I then also
increased the gain from 10 to 100 on the SR560
. This should now make the front end noise of the
seismometer/SR560 close to equal to the noise of the PEM ADC.