Transcript C-side: status and plans for current week

Chronology - I
 Year 2007 + Jan. 2008: from time to time short
circuits failures in chains supplying low voltage to
C-W bases (either +6V or -6V, ~5 lines in total):
 No more that 1-2 lines at the same time;
 In all these cases problem caused by single
malfunctioning C-W base with incorrectly soldered
electrochemical capacitance;
 End of Nov 2007: test batch of modified voltage
delivery/control boxes is installed on ECAL (3 + 4).
No problems observed for 2 months;
 Middle of Feb. 2008: all voltage delivery/control
boxes are modified;
Chronology - II
 Middle of March 2008: after power cut one short-circuited
line appears on A-side. After another switching on/off
MARATON supply another short-circuit is observed;
 9 April 2008: 5(!) short-circuited power lines on C-side.
Reasons and conditions: UNKNOWN (community keeps
silence);
All ‘after-modification’ cases show the same pattern:
 short-circuit is in +6V chains;
 short-circuit is due to not recovered fuse in the voltage delivery /
control box;
 short-circuit happens after (? incorrectly preformed ?) low voltage
power supply (MARATON) shut-down;
Brief comments on modification
Goal: stabilization and
increase of low voltage on
ECAL C-W bases
Change: new type of
(resettable) fuse in LV chains.
Fuses of old type have large
dispersion in internal
resistance R, which, together
with large value of R itself,
resulted in noticeable voltage
drop on it. As a consequence,
there is an undesirable
decrease of LV on the C-W
bases. The value of the effect
depends also on the load of
the line (i.e. number of C-W
bases served by it).
Fuse data sheet
Laboratory studies: burn tests
1.
Operational conditions check:
at U=8V no trip up to I=0.4A; Internal resistance value R is 1.6 Ohm and
does not change
2.
Trips at “soft” conditions: U=8V, I varies from 0.5 up to 3A:
1.
2.
3.
After the first trip at 0.5A R increases up to 2.3 Ohm
Next trips: fuse recovers to the value R=2.3 Ohm; recovery time is
~10min
Trips at “hard” conditions:
1.
2.
3.
high U=24V, I varies from 3 to 5A. Fuse recovers to the value R=2.3
Ohm; recovery time increases to 60 min;
Data sheet max U=30V. R increase to 3.9 Ohm, but fuse is still
operational
I=10A and U=60V. Fuse recovers to the value R=3.9Ohm; it is still
operational
Even at the abnormal current/voltage conditions, which can not be
achieved in the ECAL system, it was not possible to reproduce
an effect of non-recovery in the lab
Conclusions / proposals /
requests …
 2 versions of what is happening:
 small fraction of fuses is defective. As soon as all of them will malfunction and
replaced, the problem will disappear;
 abnormally high currents sometimes appear at the moments of ECAL LV power
sources shut-down for reasons unknown. These reasons must be understood;
 Therefore our proposal is:
 avoid unnecessary switching ON/OFF MARATON LV;
 if there is a need to switch it OFF (e.g. for preshower people) – contact us first, we
will check current ECAL conditions;
 each turning ON/OFF of MARATON should be mentioned in CALO logbook
together with the status of ECAL HV Agilent power supply;
 request to ECS group: is that possible to record automatically all moments when
MARATONS and also AGILENTs channels are turned ON/OFF?
Conclusions / proposals / requests
(cont) …
 Correct procedure to switch OFF the
ECAL:
 Set zero HV codes on ECAL PMs;
 Set zero MV on Agilent power supply;
 Switch OFF LV (MARATON). All 4 dedicated
channels of MARATON power supply must be
turned OFF at once. DO NOT TURN OFF single
channel, it can cause MARATON supply failure;