ECR Title: Add RF centering to AS wave front sensors	DCC No: E1500432-v1
Date: 2015/11/06
Requester: Keita Kawabe	Impacted Subsystem(s): ISC/ASC
Description of Proposed Change(s): Allow RF centering of AS WFS using 2xOmega (e.g. 90MHz). Each WFS head needs one 4ch IQ demodulator (D0902796) and 8ch whitening (D1002559) for this. In ASC/IO chassis, ADC card 3, CH9-CH16 currently reserved for “AS_X” spare will be used for 90MHz demod for one WFS. For the other WFS, we will use ADC 1 CH 21-28 (this card is currently only used by ASCIMC model). We do not want to reserve ADC card 3, CH 1-8 (“POP_X”) for this purpose as they are used at LLO. ASC model is changed to accommodate the new demodulated signals to produce standard PIT and YAW error, and the error points are added to the science frame as per other ASC error points. How the RF signal from WFS head is routed to the new demodulators is yet to be determined.
Reason for Change(s): Simulation suggests that 2xOmega is a better centering signal than DC. This potentially allows a better sensing of BS and SRC alignment. Also, since contrast defect is less of a problem with 45MHz SB as AS is not dark for 45MHz, 90MHz centering is expected to be less sensitive to the carrier centering, which potentially adds to the robustness of the ASC.
Estimated Cost: USD XXXX for two 4ch IQ demodulators (D0902796) and two 8ch whitening (D1002559). 4 error signals (2 WFSs, PIT and YAW) are recorded at 2kHz in science frame.
Schedule Impact Estimate: Preparation is done before the actual commissioning, and we expect about 1 week of commissioning time to make it work.
Nature of Change (check all that apply): Safety Correct Hardware Correct Documentation	Improve Hardware Improve Software Improve/Clarify Documentation Change Interface Change Requirement
Importance: Desirable for ease of use, maintenance, safety Desirable for improved performance, reliability Essential for performance, reliability Essential for function Essential for safety	Urgency: No urgency Desirable by date/event: ____________ Essential by date/event: Post-O1 commissioning Immediately (ASAP)
Impacted Hardware (select all that apply): Repair/Modify. List part & SNs: ______________________ Scrap & Replace. List part & SNs:_____________________ Installed units? List IFO, part & SNs: _________________ Future units to be built: 2 each of D0902796 and D1002559	Impacted Documentation (list all dwgs, design reports, test reports, specifications, etc.): T1100472 ADC and DAC channel usage for ISC, D090666 Impacted Software (list all that apply): ASC frontend model, both common and local.
Disposition of the proposed change(s): The disposition of this proposed engineering change request is to be completed by Systems Engineering and indicated in the “Notes and Changes” metadata field in the DCC entry for this ECR. The typical dispositions are as follows: Additional Information Required: in which case the additional information requested is defined. The ECR requester then re-submits the ECR with the new information using the same DCC number for the ECR but with the next version number. Rejected: in which case the reason(s) for the rejection are to be given Approved Approved with Caveat(s): in which case the caveat(s) are listed TRB: the ECR is referred to an ad-hoc Technical Review Board for further evaluation and recommendation. It is the System Engineer’s (or designee’s) responsibility to organize the TRB. The System Engineer (or designee) then makes a technical decision based on the TRB’s recommendation. Links to the TRB’s documentation (charge, memos, final report, etc.) are to be added to the “Related Documents” field for this ECR. CCB: a change request for approval of additional funds or schedule impact is to be submitted to the Configuration Control Board. Links to the CCB’s documentation (CR, etc.) are to be added to the “Related Documents” field for this ECR. Concurrence by Project Management: Acknowledgement/acceptance/approval of the disposition is to be indicated by the electronic “signature” feature in the DCC entry for this ECR, by one the following personnel: Systems Scientist Systems Engineer Deputy Systems Engineer