[Stefan, Koji]
Quick Summary
Shutter timing test has been performed for the OMC PZT shutter and the fast mechanical shutter. Everything seems reasonable.
- The trigger logic fires at the PD input of +2V.
- The trigger logic reacts at 1.5us since the PD input thresholding.
- The PZT shutter detunes the OMC cavity at 4.8us.
- The fast mechanical shutter start blocking the beam at 1.7ms, reaches half blocking at 1.85ms, complete block at 2.0ms.
More about the test comes later.
Shutter Test Setup (Attachment1)
- The PD signal from AS_C QPD was temporarily disconnected from the left PD port. Instead, a function generator (SRS DS345) was connected. The static offset of the func gen was used to mimic the PD signal.
- The output of the shutter logic unit (D1102312) was branched by a BNC-T.
- A thorlabs PD (PDA55, Si DCPD, BW ~10MHz) was placed on the ISCT6 to monitor the power at OMCT and OMCR for testing the PZT shutter and the fast mechanical shutter, respectively.
- The monitor signals were connected to an oscilloscope (TDS3034B). The yellow, blue, and magenta traces corresponds to the FG offset, trigger signal, and the optical power at OMCT/R.
Shutter Test Results
- The offset voltage of DS345 was manually swept from 0V to a positive voltage until the trigger fired. We confirmed that the trigger fired at 2V.
- The offset voltage was changed from 0V to 5V on DS345. This made the actual output voltage changed from 0V to ~9V. The output voltage was not so clean because the relay seemed to be switched upon the change. However this essentially does not affect the test.
- The oscilloscope traces showed that the trigger logic reacted 1.5us after the PD input crossed the threshold. (Attachment 2)
- The OMCT optical power started to drop 4.8us after the thresholding (Attachment 3) and reach 1/10 of the power after ~60us (Attachment 4). The trace for the OMCT power showed a decay curve. The half life was 10~20us depending on which part of the curve is taken. This corresponds to the cutoff freq of 5.5kHz ~ 11kHz, which is way to low and unlikely to be the cavity pole of the OMC (330kHz). It is more likely to be determined by the actual motion speed of the PZT.
- The OMCR light was used for the test of the fast mechanical shutter. During this test we didn't try to lock the OMC cavity to make the observation of the light drop easier to interpret. The shutter started blocking the beam at 1.7ms, reached half blocking at 1.85ms, completed blocking at 2.0ms. (Attachment 5). The observation in a longer time scale (~0.5s) showed that there was no boucing effect of the mechanical shutter any more. (Attachment 6)