HRC -Y Shutter Anomaly
A scheduled observation of the Crab Pulsar, ObsID 3831, requested a special
set-up for the HRC: SI_MODE OBS03831,
which included the insertion of both of the HRC shutters in front of
the HRC-S such that on-axis X-rays from only one quadrant of the HRMA
would reach the detector. An analysis of event data suggested that
only one of the shutters had moved into position. Subsequent
analysis of detector housekeeping telemetry confirmed that this
was the case.
Day 2003:269
Below are four plots of relevant HRC housekeeping telemetry for the
period covering the shutter insertion. The plots are: motor select
read-back verifiers, selected motor limit-switch status, selected
motor temperature, and HRC bus current. Each plot shows the time
of the motor select and all motor de-select commands as well as the
motor drive enable and disable commands. The +Y shutter commanding
was all nominal as were the telemetry responses. When the -Y
shutter select command was issued the motor selected read-back bit
did not indicate that the motor was selected. However, the
selected motor limit-switch status and temperature selections for
the -Y shutter did occur. There is also a possible change in the
HRC bus current when the -Y shutter is selected but the increase
from driving the motor does not occur.
Day 2003:271
Below are the similar plots as above but for the interval covering the
shutter retraction commands. Again the -Y shutter motor selection
verifier does not indicate selection of the motor while the -Y shutter
limit-switch status and temperatature are selected. Again there is
also an indication of a bus current change when the -Y shutter
motor is selected.
Possible Causes
Given the telemetry above, an HRC team review of the schematics limits
the cause of the anomaly to just a few components on the motor
select board (HRC-5224 sheet
1
2
3
4
of 4): some that
de-mux a motor select code into individual motor selected bit
(common to all motors) and some that act to supply the current to
the -Y shutter motor windings.
It has been suggested that the most-likely component is the relay that
switches the drive currents onto the motor and activates the
motor selected telemetry verifier bit. Gas evolution within the
relay may have fouled the contacts. It may be possible to clear
the contacts by repeated activate/de-activate cycles.
Last modified: Thu Oct 9 12:50:47 EDT 2003
Dr. Michael Juda
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Mail Stop 70
Cambridge, MA 02138, USA
Ph.: (617) 495-7062
Fax: (617) 495-7356
E-mail:
mjuda@cfa.harvard.edu