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MTBF Data
for SIXNET Hardware
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| SIXNET
calculates the actual installed experience of our customers in calculating
the Mean Time Between Failure (MTBF) data we publish. We use a conservative
estimate of only 70% of units shipped being in service and a usage
per day of 12 hours.
There are several methods to calculate MTBF. Most
often manufacturers quote theoretical calculations that are based
upon statistics computed about the components used in the product.
We have chosen instead to report actual results, which are gathered
from our ISO9001 traceable shipments and return/repair records.
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MTBF
Data (updated May 2005): (see
below for how we calculate MTBF)
| Product
|
#
of Units
Sampled |
Average
Units /
month
(A)
|
Total
Unit
Months
(A
x 78)
|
Total
Unit
Hours
(A
x 78 x .7
x 12 x 30)
|
Applicable
Failures |
MTBF
(see
notes) |
Ethernet
Switches |
9,135 |
761 |
59,378 |
14,963,130 |
13 |
1,151,010
|
Industrial
Modems |
5,940 |
495 |
38,610 |
9,729,720 |
19 |
512,091
|
Industrial
I/O &
Modbus Gateways |
7,787
|
649 |
50,616 |
12,755,106 |
17 |
750,300
|
| IPm-based
Controllers & RTUs |
1,110 |
93 |
7,215 |
1,818,180 |
4 |
454,545
|
Notes:
> These MTBF numbers are
based on data for a sampling of units over a time span of
one year.
> For SIXTRAK I/O, the MTBF can be broken down
such that for a system with 20
modules, there is only a 1 in 4 likelihood
that you will have a single failure in 4 years. |
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MTBF Calculation:
First,
based on a sampling of actual units, we determine the average number
of units being installed per month (A). Second, we determine the
number of months in the sampling interval (B). We then can calculate
the total number of "unit months" that these units have
been in the field (C).
((A
x 1) + (A x 2) + … + (A x B)) = C (total number of unit months
in the field)
(Note: For
a twelve-month period, you would multiply 78 times the average
number of units installed per month.)
Next, we assume
an installation rate of 70% of what we shipped and 12 hours operation
per day on the average. From this we can calculate the total number
of "unit operating hours" (D) as follows:
C
(from above) x 70% x 12 hours/day x 30 days/month = D (total number
of unit operating hours)
Finally, to
get the MTBF we divide the total number of unit operating hours
by the number of applicable failures. An applicable failure is
one that cannot be attributed to misuse (i.e. over-voltage, forklift
impalement, etc.), Mother Nature (i.e. lightning, flooding, etc.)
or other returns that are not related to manufacturing defects.
(Total
number of unit operating hours) / (number of chargeable failures)
= MTBF
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Certified
to Perform
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