jeffrey.kissel@LIGO.ORG - posted 14:55, Wednesday 31 October 2012 - last comment - 09:15, Monday 26 November 2012(4563)
H1 SUS PR2 Alignment Offsets Calibrated into [urads] of Optic Motion
Following a similar prescription as what Keiko's done at LLO (see e.g. LLO aLOG 4030), but now using the new infrastructure, I've installed a few gains, H1:SUS-PR2_M1_OPTICALIGN_P_GAIN 2.636 [drive cts/urad] H1:SUS-PR2_M1_OPTICALIGN_Y_GAIN 1.859 [drive cts/urad] into the new OPTICALIGN bank, which should now be responsible for aligning the optic. With this gain, the offsets H1:SUS-PR2_M1_OPTICALIGN_P_OFFSET (for Pitch) H1:SUS-PR2_M1_OPTICALIGN_Y_OFFSET (for Yaw) are then calibrated into [urad] of optic motion. This gain should be [applicable to / the same for] every HSTS. I attach some shots of the new screens demonstrating where these gains live (and showing off the new screens). ----------------------------- How the gain was calculated: It's along signal chain, but here goes (I use Yaw on an HSTS as an example): LF +--------+ +------+ +-----------+ +-----------+ +---------+ +->|COILOUTF|->| DAC |->|Coil Driver|->|Coil/Magnet|->|Lever Arm|->+ +-----------------+ +---------------+ +----------+ +--------+ | +[cts/ct]+ +[V/ct]+ +---[A/V]---+ +---[N/A]---+ +---[m]---+ | +-------------+ +------------------+ |OPTICALIGN OFFSET|->|OPTICALIGN GAIN|->|DRIVEALIGN|->|EUL2OSEM|->+ +->|HSTS M1 to M3|-->|Optic Displacement| +-----[urad]------+ +---[cts/urad]--+ +-[cts/ct]-+ +[cts/ct]+ | +--------+ +------+ +-----------+ +-----------+ +---------+ | +--[rad/N.m]--+ +------[urad]------+ +->|COILOUTF|->| DAC |->|Coil Driver|->|Coil/Magnet|->|Lever Arm|->+ RT +[cts/ct]+ +[V/ct]+ +---[A/V]---+ +---[N/A]---+ +---[m]---+ (see fullsignalchain.png if you browser sucks at ASCII art) Thankfully, because - we're only looking for the DC gain of this path, - the DRIVEALIGN matrix is an identity at this point - the EUL2OSEM matrix accounts for (divides out) the number of actuators (two in this case) and the lever arm between the OSEM and the center of rotation - the COILOUTFs are unity at DC then our calculation only involves this simplified chain: +-----------------+ +---------------+ +------+ +-----------+ +-----------+ +-------------+ +------------------+ |OPTICALIGN OFFSET|->|OPTICALIGN GAIN|->| DAC |--|Coil Driver|--|Coil/Magnet|->|HSTS M1 to M3|-->|Optic Displacement| +-----[urad]------+ +---[cts/urad]--+ +[V/ct]+ +---[A/V]---+ +-["N.m"/A]-+ +--[rad/N.m]--+ +------[urad]------+ (see reducedsignalchain.png if you browser sucks at ASCII art) which means the OPTICALIGN GAIN is: OPTICALIGN GAIN [cts/urad] = ( DAC [V/ct] * Coil Driver [A/V] * Coil/Magnet [N/A] * HSTS M1 to M3 [rad/N.m] * 1e6 [urad/rad] )^-1 = ( (20/2^18) * 0.011919 * 0.963 * 0.4332 (for Yaw) * 1e6 )^-1 = 1.850 [cts/urad] The only difference for pitch is that HSTS M1 to M3 [rad/N.m] = 0.6172 (for Pitch). The electronics gains of the signal chain were taken from T1000061 (the contents of which have been experimentally confirmed elsewhere), and the HSTS M1 to M3 coefficients were taken from the production model (e.g. see T1200404).
Images attached to this report
Comments related to this report
S. Aston, J. Kissel As with the QUAD (see LHO aLOG 4746), I have made mistakes in the OPTICALIGN gain calculation (shown above) in that, though the spelled out calculation is correct (with a "DC" compliance of 0.6172 [rad/N.m] (for Pitch), and 0.4332 [rad/N.m] (for Yaw)), the answer I call out has the values for Pitch and Yaw flipped. Even further, after double checking the DC compliance numbers using the HSTS model, I discovered that, for "DC," I used the value of the transfer function at 0.1 Hz. However, the transfer functions have not yet truly flattened by that point as the values at 0.01 Hz are: M1 P to M3 P: 0.609 [rad/N.m] M1 Y to M3 Y: 0.426 [rad/N.m] Sheesh. I clearly did these calculations far too quickly, or at least was far too hasty with my copy-and-pasting. Thanks to Stuart for catching them! So, redoing it slower, with the 0.01 Hz numbers for the "DC" compliance, the calculation should read: (FOR AN HSTS) OPTICALIGN GAIN [cts/urad] = ( DAC [V/ct] * Coil Driver [A/V] * Coil/Magnet [N/A] * HSTS M1 to M3 [rad/N.m] * 1e6 [urad/rad] )^-1 = ( (20/2^18) * 0.011919 * 0.963 * 0.609 (for Pitch) * 1e6 )^-1 = 1.8751 [cts/urad] (for Pitch) OPTICALIGN GAIN [cts/urad] = ( DAC [V/ct] * Coil Driver [A/V] * Coil/Magnet [N/A] * HSTS M1 to M3 [rad/N.m] * 1e6 [urad/rad] )^-1 = ( (20/2^18) * 0.011919 * 0.963 * 0.426 (for Yaw) * 1e6 )^-1 = 2.6806 [cts/urad] (for Yaw) As of this entry, I have corrected these gain values in H1 SUS PR2, saved a new h1suspr2_safe.snap, and committed it to the userapps repo, /opt/rtcds/userapps/release/sus/h1/burtfiles/pr2/h1suspr2_safe.snap