Download Reliability analysis with isograph

Student meeting
27.05.2013
Reliability analysis of the Input
Monitor in the BLEDP
Vegard Joa Moseng
BI - BL
Overview:
 From «The new BLM system for the injector complex»
 BI DAY 2012 – William Viganò
The circuit:
Measurement Methods
 The input monitoring system has two
different measurement levels.
 One is the Fully Differential Frequency
Converter (FDFC) which measures detector
output currents from 10pA to 30mA. In this
measurement method, the ADC is attached
to the diff. output of an integrator in the
input monitor.
 The other is the Direct ADC Acquisition
(DADC) which measure detector output
currents from 80uA to 200mA. The ADC is
attached to an input resistor on which the
voltage drop is measured.
Operation
 The input monitor is responsible for
processing the information by the
monitors, into a value that is usable for the
FPGA and its algorithms.
About the Input
Monitor circuit
Criticality
 For each detector connected to the BLEDP,
there is one input monitor circuit and one
ADC. There is therefore 8 input monitor and
ADC circuits per BLEDP.
 The input monitor and the ADC is critical for
the operation of both the measurement
methods, and is thus critical for one channel
in the BLEDP. Therefore, the loss of an ADC is
equivalent to the loss of a detector.
 The Input Monitor and the ADC have two main
failure modes that affect the operation of the
BLEDP; complete failure (no output), and
erroneous output (from either internal failures
or erroneous inputs).
Detection
 As a part of the new acquisition system, an
improved connectivity check is planned to
be implemented which is capable of
frequently testing the entire detector
supply chain. This should therefore be able
to detect a erroneous output by it’s
reference current. This will however not
indicate explicitly that the ADC is giving
erroneous outputs but it will be sufficient
for a false dump to take place and the
changing of the BLEDP card, and thus
maintaining the operation of the machines
without there being a blind failure.
Integration in
the system
The block arrangement
 To simplify the analyses and to make it easier for the
readers to identify important information, the report
is constructed in blocks rather than components. For
the blocks, the important failure modes for the
individual components have been added to make sure
all components have been evaluated and that the
crucial information is preserved in the report.
 The blocks are (FM = Failure modes – 117 in total):
1. Digital potentiometer block (5 FM)
2. Saturation monitoring block (17 FM)
3. Stop function block (4 FM)
4. Switch FDFC / DADC to ADC block (4 FM)
5. Buffer amplifier block (14 FM)
6. Voltage reference generator block (7 FM)
7. Comparators block (13 FM)
8. Flip-Flop block (9 FM)
9. Offset current and detector input block (9 FM)
10. Switch FDFC - DADC to Input Switch (4 FM)
11. Input switch block (4 FM)
12. Fully differential integrator block (12 FM)
13. Power supply for digital potentiometer block (4 FM)
14. Input voltage filtering block (3 FM)
15. Other filtering blocks (8 FM)
Block system
MTTF:
 The value is for a single circuit. For the
BLEDP the card will have 8 Input Monitor
and ADC circuits, which means that the
overall MTTF for the BLEDP will be a
weighted average of all the circuits.
 Failure rate (1x Input Monitor): 2.757E-06
 MTTF in hours: 3.627E+5
 MTTF in years: ~41 years
Severity ranking
 1. No effect: Non-critical failure such as
filtering.
 2. Maintenance: Failure in redundant
components and other failures that allow
for continued operation but should be fixed
as soon as possible.
 3. False dump: Failures that causes loss of
critical functionality and/or safety, will
cause the system to abort (dump the
beam).
 4. Blind failure: Failures where you are
unable to detect erroneous information, or
where you have no protection when you
expect to have .
Reliability
analysis
1000
100
Highest
indidual
10
Combined
Severity
Occurence
Detection
RPN(SxOxD)
1
Total:
Severity = 351
Occurrence = 1
Detection = 1
RPN = (3x1x1)117 = 351
Risk Priority
Numbers
A total of 117 failure modes for
random failures in the Input monitor
circuit will cause a failure
inconsistent with a good operation
and in most cases these will cause
the beam to be dumped in the next
possible dump site. However, the
individual probability of the failures
are so low that they are considered
highly unlikely. Satisfactory detection
is also implemented, meaning there
are no failures that will manifest as a
blind failure. Given the overall low
probability and reliability focused
design, no special action is
warranted.
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