SITCOMTN-095: M1M3 - Settling time after a slew

  • Nacho Sevilla Noarbe

Latest Revision: 2024-02-15

Note

This technote is a work-in-progress.

1 Abstract

This is the technote for the settling time after a slew analysis on the TMA with M1M3. We measured the mirror cell settling time (position and rotation) after a slew.

Currently the test fails marginally looking at movements for a 4 hour long soak test. The IMS repeatability and precision are measured on a specific data set and the requirements for it are PASSED too.

1.1 Requirements

LTS-88-REQ-0051

3 SITCOM-1172: M1M3 - Analyze settling times after a slew statistically

3.1 Requirement verified

LTS-88-REQ-0051: The positioning system SHALL be able to meet all its requirements within 3 seconds of ending a short slew (3.5 degrees in 2 seconds)

The requirement is for the system to have settled to the same (within precision) position after a short slew, within 3 seconds.

3.2 Test Case

LVV-11258

Plot the settling time of the M1M3 for X, Y, Z, RX, RY, and RZ.

The data comes from the EFD: imsData. The IMS is the Independent Measurement System, a set of electronic micrometers that measure the displacement of the M1M3 mirror with respect to the cell. According to LTS-88 it has a 4 um accuracy in XYZ and 3e-5 degree accuracy in RXRYRZ.

3.3 Test Data

  • dayObs = 2023-12-20

  • block = 146, soak tests (operations like)

  • selected all events of type = SLEW ending in TRACKING, a total of 227 events

3.4 Results

Out of the 227 events, 167 had at least one failure, defined as one of the position or rotation columns from the IMS being above the repeatability requirement for the IMS at any point between the 1 second mark after the slew, and 15 seconds after it (checked for RMS and bias).

_images/mean_position.png

Figure 1 Value of the IMS position absolute bias for all axes combined at exactly 1 second after the slew stop.

_images/mean_position_xyz.png

Figure 2 Value of the IMS position absolute bias for each axis at exactly 1 second after the slew stop.

_images/mean_rotation.png

Figure 3 Value of the IMS rotation absolute bias for all axes combined at exactly 1 second after the slew stop.

_images/rms_position.png

Figure 4 Value of the IMS position RMS for all axes combined at exactly 1 second after the slew stop.

_images/rms_rotation.png

Figure 5 Value of the IMS position RMS for all axes combined at exactly 1 second after the slew stop.

4 Conclusions

The requirement is failed at 1 second after slew stop due to a failure in the yPosition column, on approximately 70% of the cases in which it averages a 3 micron displacement due to a slow drift of the cell. In addition, there seems to be multiple failures due to RMS or mean going over the requirement at some point in the following 15 second span.