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kenta.tanaka - 3:09 Wednesday 09 November 2022 (22841) Print this report
Beacon excitation test from DGS

### Abstract

I tried to send the 24 kHz excitation signal from the 64 kHz DGS model to ETMX to excite the drumhead mode. I confirmed the 24 kHz beacon signal from ETMX is in the CARM signal, so we can excite the drumhead mode with DGS. 

### What I did

  • As the previous report, I prepared the 64 kHz model for exciting the drumhead mode of ETMX (klog22648) and installed the summing adaptor to mix the 24 kHz excitation signal to the usual signals (klog22798).
  • I made the medm screen for sending the 24 kHz excitaion signal to ETMX (fig. 1). You can access the screen from "OMC BEACON" button in OMC dock (fig. 2).
  • After FPMI lock, I sent the 23.6911 kHz signal to ETMX. I set the amplitude to 30000 cnts at this time. I find the beacon signal from drumhead mode in CARM signal. (fig. 3) (Actually, I want to see whether the signal is in DARM but Moku connected to DARM port was not responded.) 
  • However, The amplitude seems very smaller than the analog method (klog22622). I consider the cause later.
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Comments to this report:
kenta.tanaka - 18:45 Wednesday 09 November 2022 (22849) Print this report

Yokozawa-san taught me (and I completely forgot ) that the gain of AI filters around 20 kHz is -20 dB because there is a steep low pass filter whose cutoff frequency is 10 kHz. If we estimate the magnitude of the signal sent with the analog setup and the magnitude of the signal sent with DGS, it is exactly one-tenth, and the amplitude of the drumhead mode is also exactly one-tenth, so I think it is consistent.

So I just remember to change the cutoff frequency of the AI filter to excite ETMX at 24kHz  

  • Analog setup: the voltage at the input port HP coil driver = (Excitation amplitude from Moku:lab) * (the gain of SR560) * (the gain of summing adaptor) = 2Vpp * 5* 1/5.4 ~ 1.85
  • DGS setup:  the voltage at the input port HP coil driver = (Excitation amplitude from DGS) * (cnt2V of DAC) * (the gain of AI filter) *(the gain of summing adaptor) = 60000 cnts-pp * 10Vpp/2^16 cnts * 1/10 *1/5.7 ~ 0.175
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