NAOJ GW Elog Logbook 3.2
Displaying report 1-1 of 1.
PierrePrat - 22:14, Tuesday 02 April 2019 (1271)
Modification of the GRMC Servo-filter
The following settings and modifications were done for the GRMC Servo-filter to the original Servo-filter which electronic schematics and bill of material are saved on the wiki.
1-Setting of switches on the front panel:
* The differentiator shall be disabled on the front panel in setting the switch on "OFF".
* The switch INV/NON INV on the front panel, shall be set on INV.
2-Setting of the 8 straps on the board:
Low-pass filter, Notch filter 1 and notch filter 2 are activated on the board in setting strap on connectors P7, P8 and P9 (3 pins) between pins 1 and 2
* The transmission signal is positive with a peak at about 2.6V.
It shall be inverted: the strap on connector P4 (3 pins) is set between pin 2 and 3.
The threshold level must be tuned to -1.3V (THRESHOLD OUT).
* Strap is set on connector P11 (3 pins), between pins 2 and 3, in order to activate the sample-and-hold on the triangular signal, on the locking.
* Strap is set on connector P3 (2 pins) to connect the triangular signal to the output stage.
* Strap is set on connector P2 (3 pins), between pins 1 and 2, for test purpose.
To check low-pass filter, notch 1 and notch 2 filters (in scan mode) between TEST IN and TEST OUT. For this test the differentiator, shall be set on "ON" (not intuitive but important). After this test, the differentiator shall be disabled the front panel in setting the switch on "OFF".
* Strap is set on connector P1 (2 pins), in order to be able to tune the offset.
3-Modification of components:
* Integrator 1/f: corner frequency changed to 2.2 kHz
Capacitor CMS 1206: C38 = 33nF
* Integrator 1/f2: corner frequency changed to 220 Hz
Capacitor CMS 1206: C26 = C33 = 330nF
* Low-pass filter: cut-off frequency changed to 2.2 kHz
Capacitor CMS 0805 : C45 = 2.2nF
Resistor CMS 1206 : R59 = 33k
* Notch filter 1: notch frequency changed to 7.23 kHz / quality factor changed to 3.6 (measured)
Capacitor CMS 0805 1% : C49 ; C50 ; C51 ; C53 = 2.2nF
[Resistor CMS 1206 : R65 ; R66 ; R67 ; R68 = unchanged (10k)]
Resistor CMS 1206 : R73 = 2.7k
* Notch filter 2: notch frequency changed to 11.85 kHz / quality factor changed to 0.9 (measured)
[Capacitor CMS 0805 1% : C60 ; C61 ; C62 ; C63 = unchanged (560 pF)]
Resistor CMS 1206 : R79 ; R80 ; R81 ; R82 = 24k
Resistor CMS 1206: R89 = 13k
* Gain adjustment (G): Gmin = 0.007125 / Gmax = 0.285 / Gtyp = 0.045
Resistor CMS 1206: R33 = 1.3k
Resistors CMS 1206: R5 ; R7 = 10k
1-Setting of switches on the front panel:
* The differentiator shall be disabled on the front panel in setting the switch on "OFF".
* The switch INV/NON INV on the front panel, shall be set on INV.
2-Setting of the 8 straps on the board:
Low-pass filter, Notch filter 1 and notch filter 2 are activated on the board in setting strap on connectors P7, P8 and P9 (3 pins) between pins 1 and 2
* The transmission signal is positive with a peak at about 2.6V.
It shall be inverted: the strap on connector P4 (3 pins) is set between pin 2 and 3.
The threshold level must be tuned to -1.3V (THRESHOLD OUT).
* Strap is set on connector P11 (3 pins), between pins 2 and 3, in order to activate the sample-and-hold on the triangular signal, on the locking.
* Strap is set on connector P3 (2 pins) to connect the triangular signal to the output stage.
* Strap is set on connector P2 (3 pins), between pins 1 and 2, for test purpose.
To check low-pass filter, notch 1 and notch 2 filters (in scan mode) between TEST IN and TEST OUT. For this test the differentiator, shall be set on "ON" (not intuitive but important). After this test, the differentiator shall be disabled the front panel in setting the switch on "OFF".
* Strap is set on connector P1 (2 pins), in order to be able to tune the offset.
3-Modification of components:
* Integrator 1/f: corner frequency changed to 2.2 kHz
Capacitor CMS 1206: C38 = 33nF
* Integrator 1/f2: corner frequency changed to 220 Hz
Capacitor CMS 1206: C26 = C33 = 330nF
* Low-pass filter: cut-off frequency changed to 2.2 kHz
Capacitor CMS 0805 : C45 = 2.2nF
Resistor CMS 1206 : R59 = 33k
* Notch filter 1: notch frequency changed to 7.23 kHz / quality factor changed to 3.6 (measured)
Capacitor CMS 0805 1% : C49 ; C50 ; C51 ; C53 = 2.2nF
[Resistor CMS 1206 : R65 ; R66 ; R67 ; R68 = unchanged (10k)]
Resistor CMS 1206 : R73 = 2.7k
* Notch filter 2: notch frequency changed to 11.85 kHz / quality factor changed to 0.9 (measured)
[Capacitor CMS 0805 1% : C60 ; C61 ; C62 ; C63 = unchanged (560 pF)]
Resistor CMS 1206 : R79 ; R80 ; R81 ; R82 = 24k
Resistor CMS 1206: R89 = 13k
* Gain adjustment (G): Gmin = 0.007125 / Gmax = 0.285 / Gtyp = 0.045
Resistor CMS 1206: R33 = 1.3k
Resistors CMS 1206: R5 ; R7 = 10k
Recently, it is found that GRMC loop cannot be closed. To check what is the problem, I disconnected the slow scan of MZ and put MZ PZT offset to a value that GRMC transmission is the highest. After that, according to the original setting, I have done following checks
0. GRMC has a good alignment.
1. PDH signal has 316mV pk-pk checked from EPS1.
2. GRMC has loop sign of INV, which is as design.
3. The RF source phase is reloaded. The phase of RF source is 125deg. When it is changed to 35deg, the signal around resonance becomes flat. This indicates the RF signal phase is still a good one.
4. There is a switch which has +/- sign. This doesn't decide the sign of control loop. But when we use this type of servo for CC1/2 controls, we need to flip this switch. I tried to flip this switch, but it doesn't help to close loop.
5. GRMC transmission is checked to have 1.13V peak. This is two times smaller than the value written by Pierre.
6. Loop gain is 3 as usually used.
7. Threshold for peak identification is -0.55V. This is as required.
8. The GR power reaching AOM is measured to be 44mW, whose nominal value is 50mW.
These checks show little issues but they should not prevent the GRMC locking. More investigation is required.