1. MPP Result of the investigation in the orbit correctors faults.
RCBV27.L6B2 – High value of magnet resistance during PNO.a1
RCBCV10.L6B1 – EE811 voltage tap missing

2. RCBV27.L6B2 – Status of PNO.a1 analysis on 16/04/2008
Status faced when the test PNO.a1 was executed (16/04/2008):
The resistance of the magnet is higher than the criteria !!

3. RCBV27.L6B2 – PNO.a1 – Current cycle and circuit

4. RCBV27.L6B2 – PNO.a1 – Criteria and calculation
U_TOT = V_MEAS – (U_LEAD_POS + U_LEAD_NEG) – U(R_serie)
During plateau:
R_Magnet = U_TOT / I_PNO
<3.5 e-3 Ohm
Edms :
R_serie = R_Cable_Pos
+ R_Cable_Neg
Data from 16/04/08 during plateau:
V_Meas= 2.63 V; U_LEADs=0.068 V U(R_serie)= 2.81 V.
R_Magnet = -4.5e-3 Above the limit and negative !!
Measurement of R_serie repeated 05/05/2008  Ohm
R_Magnet updated: 1.08 e-3 Ohm, OK !!
(with offset corrections)
LHC Layout Database
( )
R_serie=0.051 Ohm
LHC Layout Database
( )
R_serie= Ohm

5. RCBV27.L6B2 – PNO.a1 – PASSED with the updated R_serie

6. RCBV27.L6B2
Conclusion:
The PNO.a1 cycle should be repeated on RCBV27.L6B2 in order to make sure that the measurement of DC warm cables performed on 05/05/2008 did not altered the circuit.
Then the NC should be closed.

7. MPP Result of the investigation in the orbit correctors faults.
RCBV27.L6B2 – High value of magnet resistance during PNO.a1
RCBCV10.L6B1 – EE811 voltage tap missing 7

8. RCBCV10.L6B1 – EE811 voltage tap missing
Chronology of events:
On 11/03/2008, RCBCV10.L6B1 circuit was successfully qualified by ELQA team.
On 14/04/2008, AB/PO can not power this circuit, they have a fault on the PC.
On 16/04/2008, EE811 (cold voltage tap) is found open, directly from the feed through pin coming from the cover flange => NC opened. 8

9. RCBCV10.L6B1 – EE811 voltage tap missing
On 05/05/2008:
Intervention to perform a time domain reflectometry to localize precisely the defect. It is repairable if it is at the level of the cover flange.
Surprise! The voltage tap EE811 is back!
Impossible to make a reflectometry as there is no defect anymore, so I did a few ohmic measurements to check all the voltage taps.

10. RCBCV10.L6B1 – EE811 voltage tap missing
Measurements on the external « sick » orbit dipole:
For comparison, measurements on the internal dipole:
*: Measurement performed with a portable multimeter.

11. RCBCV10.L6B1 – EE811 voltage tap missing
Conclusion:
AB/PO have no more interlocks, they can now power the magnet to qualify the circuit (checked with V. Montabonnet) with the circuit as is.
Proposal:
We could try to reproduce the defect, by feeding a current of 2 Amps through the voltage taps.
If the voltage tap remains connected, we close the NC.
If we manage to open the vtap, we perform a time domain reflectometry.