The following settings and modifications were done for the IRMC 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 reflection signal is negative with a base at about -600mV (after the change of the trans-impedance resistor of the photodetector from 51 Ohm to 510 Ohm ).
It shall be inverted: the strap on connector P4 (3 pins) is set between pin 2 and 3.
The threshold level must normally be tuned to a positive level of +300mV (THRESHOLD OUT).
In practice, we had best result with a threshold level of about +500mV.
We had also to increase the sample-hold capacitor (C89). See below.
* 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 154 Hz
Capacitor CMS 1206: C38 = 470nF
* Integrator 1/f2: corner frequency changed to 220 Hz
Capacitor CMS 1206: C26 = C33 = 330nF
* Low-pass filter: cut-off frequency changed to 154 Hz
Capacitor CMS 0805 : C45 = 2.2nF (0805) + 270nF (through capacitor)
Resistor CMS 1206 : R59 = 3.9k
* Notch filter 1: notch frequency changed to 11.85 kHz / quality factor changed to 3 (measured)
[Capacitor CMS 0805 1% : C49 ; C50 ; C51 ; C53 = unchanged (560 pF)]
Resistor CMS 1206 : R65 ; R66 ; R67 ; R68 = 24k
Resistor CMS 1206 : R73 = 2.7k
* Notch filter 2: notch frequency changed to 17.75 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 = 16k
Resistor CMS 1206: R89 = 13k
* Gain adjustment (G): Gmin = 0.0125 / Gmax = 0.5 / Gtyp = 0.1ÂÂ
Resistor CMS 1206 : R33 = 2.2k
Resistor CMS 1206 : R5 = 10k
Resistor CMS 1206 : R7 = 10k
* Modification of threshold circuit in order to have a better tuning.
Resistor CMS 1206 : R108 = 1M (hysteresis resistor).
Resistor 2k added between pin 1 of the J14 connector and the wire (red) going to potentiometer 2k on front panel
Resistor 2k added between pin 3 of the J14 connector and the wire (blue) going to potentiometer 2k on front panel
* Modification of he sample-hold capacitance on the triangular signal:
Capacitor 1206 of 4.7microFarad added on the 1microFarad capacitor (C89).