Meggitt Sensing Systems Mean time before failure rate

Meggitt Sensing Systems Mean time before failure rate
Meggitt Sensing Systems
Mean time before failure rate
The 786 series offers the longest MTBF rate in the industry providing continuous cost savings and
reliable performance for 25 years.
MTBF
Components for 786 series sensors
Mean time between failures (MTBF)
represents the average expected time
that will elapse between failures of like
units under like conditions. Purchasers
should consider MTBF of sensors before
buying them. Accelerometers with a low
(short) MTBF result in higher costs due
to the manpower required for troubleshooting, replacement of faulty
accelerometers and lost data associated
with the more frequent failures.
Total hybrid failure rate (λρ)
The Department of Defense developed a calculation to be
used for electronic systems and circuits. Military
Handbook MIL-HDBK-217 provides guidance for computing the MTBF for hermetically sealed electronic circuits.
The 786A is sealed to a leak rate of 1 x 10-8 cc/sec and is
considered to be truly hermetically sealed. An analysis of
failures indicates that the hybrid circuit board and
connections are the only parts to fail due to normal
environmental exposure. The piezoelectric sensing
element does not play a significant role in failures.
λρ = [ΣNCλC] (1 + 0.2 πE) πF πQ πL failures per 1,000,000 hours
Where
NC = number of each particular component
λC = failure rate of each particular component
πE = environmental factor
πF = hybrid function factor
πQ = quality (screening) factor
πL = longevity (experience) factor
N is determined from the part or connection count, all other
factors are determined through reference to MIL-HDBK-217 for
the particular component or element.
Meggitt Sensing Systems
20511 Seneca Meadows Parkway
Germantown MD 20876, USA
Tel: +1 (301) 330 8811
Fax: +1 (301) 330 8873
wilcoxon@meggitt.com
www.wilcoxon.com
www.meggittsensingsystems.com
N components/elements 60° C
120° C
48 connections
0.018122
0.018122
4 plated through holes
0.000041
0.000041
1 crystal
0.0058
0.0058
1 bipolar transistor
0.00029
0.000773
1 FET
0.0135
0.0324
3 diodes
0.00731
0.027655
3 capacitors
0.16082
0.13992
5 resistors
0.00363
0.00594
Individual NCλC
0.064775 0.230651
Calculated total hybrid failure rate of 786A
Total hybrid failure rate at 60° C
λρ
= [0.064775] 70.18
= 4.5459 per 106 hrs
= 219,978 hours MTBF (25 years)
Total hybrid failure rate at 120° C
λρ
= [0.230651] 70.18
= 16.187087 per 106 hrs
= 61,778 hours MTBF (7 years)
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