ECR Title: ECR: DC Photodiodes for laser power measurement	DCC No: E12xxxxx-vx
Date: 10/2/2012
Requester: Daniel Sigg	Impacted Subsystem(s): ISC
Description of Proposed Change(s): Add DC photodiodes to the ISC/ALS system to aid the slow controls logic. We propose to add DC photodiodes (Thorlabs SM05PD1A or SM1PD1A) to: (1) the beam leaving the fiber in the correct polarization, (2) the corresponding rejected beam, (3) the IR beam of the ALS laser, (4) the PSL beam reaching ISCHT1L, (5) the green beam after the SHG, (6) and the green beam of coming back from each arm. We also propose to add 1-2 spare readout channels to each ISC table. This requires a total of 4 new auxiliary concentrators (D1201345, D1201349 and D1201352) with either 2 or 3 dual DC photodiode amplifiers (D1200543).
Reason for Change(s): A computer controlled auto-locker is at a disadvantage when it has not enough basic information. To have well defined state transitions and error conditions we need to record the laser power at the ALS laser (IR), the output of the fiber for both polarization states, the PSL beam reaching ISCHT1L, the beam after the SHG as well as both green beams returned from the arms.
Estimated Cost: 10 photodiodes/ifo (plus feedthroughs, cabling & mounting): $2500 4 concentrators/ifo (plus EtherCAT terminals): $4000 Total (3 ifos): $19500
Schedule Impact Estimate: None.
Nature of Change (check all that apply): Safety Correct Hardware Correct Documentation	Improve Hardware 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: _Feb 2013____ Essential by date/event: ____________ 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	Impacted Documentation (list all dwgs, design reports, test reports, specifications, etc.): D1100683, T1100472, D1002803, D1001423, D1100670, D1100170, D1101904, D1200196, D1200666, D1101126
Disposition (to be completed by Systems Engineering): TRB CCB Approved Additional information required. Define: [Requester re-submits with new information with the same DCC E-number for the ECR but the next version number.] Concurrence by Project Management: (Acknowledged Electronically in DCC) Project Systems Engineer: Dennis Coyne Project Systems Scientist: Peter Fritschel