on the availability and regulation of
these gases. The gases, supplied by
about 300 different cylinders (Figure
1), are a precious commodity, ranging in cost from $800 to $17,000 per
cylinder.
For years, like many older fabs, monitoring gas cylinder levels has been a
manual process. At Micrel, once every
12-hour shift, an employee armed
with a clipboard has to walk to each
gas cylinder location and manually
check the pressure regulator gauges
and/or the weigh scale depending
on the gas type. This process takes
about four hours each time or about
eight labor-hours per day. By 2001,
a bar code system was employed
to identify each gas cylinder, but an
employee was still required to manually read and record each data point,
so the process was labor-intensive
and error-prone.
In addition to monitoring gas levels
manually, to further reduce risk of
low or empty cylinders, gases were
typically replaced on a regular schedule— which meant that a given cylinder might be changed out even if it is
a quarter or even a third full. Despite
these precautions, gas supply disruptions still periodically occurred due to
unforeseen circumstances (e.g. cold
weather impacts which can condense
a gas) and were not discovered with
the manual rounds. Such disruptions
often resulted in lost yield and process downtime, which translated into
additional operational expense.
As these gas and downtime related
expenditures continued to add up
Wireless Gauge Reader
$0
$1,200
$50
Wired Transducer
$1,000
$300
$1,500
Process Downtime (Est)
Transducer/Sensor
Installation/Wiring Labor,
Materials, Design
Bring legacy system up to
the present day safety/fire
codes (where applicable)
$0 $1,000
I/O Panel Termination $0 $200
Total Cost (per point) $1,250 $4,000
Table 1. Comparison of installed cost-per-point for traditional transducers
vs. wireless gauge readers
Table 2. Savings from wireless gauge reader and wireless transducer reader
year after year, it became clear that
this situation needed to be addressed.
Operations management needed to
find new ways to better utilize manpower, ensure gases were expended
before replacing bottles, and proactively detect situations that could
cause downtime.
Table 3. Payback Analysis for Wireless Gauge Reader and Wireless Transducer Reader
Cost per point for WGRs $1,250
Number of Points installed 100
Total Cost of WGR Systems $125,000
Payback period (based on annual savings of $215,000) 7.0 Months
Evaluation of Traditional
Automation Solution
Micrel considered replacing manual
gauges with all-new transducer-based gas panels, which would automate the monitoring of gas levels.
However, making this change would
require Micrel to stop the affected
