Jan. 22, 2021

with Alex R., Alex W., Jana, Chris F., Chris O., Matt, Silke

Discussion

georgi: 100eV photon scan range over 100 seconds. 1eV/s. few microeV change per shot at 1MHz. need precision 100 microev? need to take out shot intensity (normalization)

Alex R. says encoder has 100 microev resolution, scan even faster than 1eV/s required.

Corresponds to 10kHz measurements.

silke says that old lcls1 can't be reused. old usdusb one: relative encoder (quadrature pulses) new one: absolute encoder

alex says: new encoder can only read out at 10kHz, maybe 20kHz.

zach says: add a second encoder? relative quadrature encoders faster, maybe a MHz?

silke says: "usb4" relative encoder can go up to 15MHz, but not enough space in the vacuum environment. alex found another renishaw that goes up to 15MHz.

zach asks: why not put it on the external shaft? georgi replies not straightforward to use that as the position of the grating. zach/Alex say it could be calibrated

cpo says: interpolate? georgi says the turnaround point would break interpolation. cpo says: mechanical motor turnaround time either fast or slow on timescale of 10kHz sampling should work.  in particular, turnaround time feels likely much slower than 10kHz sampling period?

alex w.: could add time-staggered 10kHz encoders to artificially increase rate

georgi says: need to understand the upper limits. interpolation may be too short-sighted. fast encoder is best.

alex wallace renishaw: https://www.renishaw.com/en/tonic-uhv-incremental-encoder-system-with-rslm20-linear-scale--11155

ankush encoder document: https://docs.google.com/document/d/1Ho1IpT4903wkUoJMV06z5hou9to5CfAgtJBDPdBl6I4/edit?ts=600b806d

Matt says we may have an existing board that could do the readout/timestamping

Summary of Options/Information

• 10kHz with interpolation?
• multiple encoders?
  • combine absolute/relative (may be complexity issues)
  • 2 staggered slower encoders
• need fpga timestamping
• 100 microev resolution requirement

To do

• fill out the table options and costs (alex and silke)
• talk to mechanical engineers (Georgi)
• meet in two weeks