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Appendix B Calibration
Frequency
Recommendation
Appendix C: Calibration
Frequency
One of the most common questions
that we are asked at Biosystems is:
“How often should I calibrate my
gas detector?”
Sensor Reliability and Accuracy
Today’s sensors are designed to
provide years of reliable service. In
fact, many sensors are designed so
that with normal use they will only
lose 5% of their sensitivity per year
or 10% over a two-year period.
Given this, it should be possible to
use a sensor for up to two full years
without any significant loss of
sensitivity.
Verification of Accuracy
With so many reasons why a
sensor can lose sensitivity and
given the fact that dependable
sensors can be key to survival in a
hazardous environment, frequent
verification of sensor performance
is paramount.
There is only one sure way to verify
that a sensor can respond to the
gas for which it is designed. That is
to expose it to a known
concentration of target gas and
compare the reading with the
concentration of the gas. This is
referred to as a “bump” test. This
test is very simple and takes only a
few seconds to accomplish. The
safest course of action is to do a
“bump” test prior to each day’s
use*. It is not necessary to make a
calibration adjustment if the
readings fall between 90%** and
120% of the expected value. As an
example, if a CO sensor is checked
using a gas concentration of 50
PPM it is not necessary to perform
a calibration unless the readings
are either below 45 PPM or above
60 PPM.
* The Canadian Standards
Association (CSA) requires the
LEL sensor to be bump tested
prior to each day’s use with
calibration gas containing
between 25% and 50% LEL.
** The Canadian Standards
Association (CSA) requires the
instrument to undergo
calibration when the displayed
value during a bump test fails to
fall between 100% and 120% of
the expected value for the gas.
Lengthening the Intervals between
Verification of Accuracy
We are often asked whether there are
any circumstances in which the period
between accuracy checks may be
lengthened.
Biosystems is not the only
manufacturer to be asked this
question! One of the professional
organizations to which Biosystems
belongs is the Industrial Safety
Equipment Association (ISEA). The
“Instrument Products” group of this
organization has been very active in
developing a protocol to clarify the
minimum conditions under which the
interval between accuracy checks
may be lengthened.
A number of leading gas detection
equipment manufacturers have
participated in the development of the
ISEA guidelines concerning
calibration frequency. Biosystems
procedures closely follow these
guidelines.
If your operating procedures do not
permit daily checking of the sensors,
Biosystems recommends the
following procedure to establish a
safe and prudent accuracy check
schedule for your Biosystems
instruments:
1. During a period of initial use of at
least 10 days in the intended
atmosphere, check the sensor
response daily to be sure there is
nothing in the atmosphere that is
poisoning the sensor(s). The
period of initial use must be of
sufficient duration to ensure that
the sensors are exposed to all
conditions that might have an
adverse effect on the sensors.
2. If these tests demonstrate that it
is not necessary to make
adjustments, the time between
checks may be lengthened. The
interval between accuracy
checking should not exceed 30
days.
3. When the interval has been
extended the toxic and
combustible gas sensors should
be replaced immediately upon
warranty expiration. This will
minimize the risk of failure during
the interval between sensor
checks.
4. The history of the instrument
response between verifications
should be kept. Any conditions,
incidents, experiences, or
exposure to contaminants that
might have an adverse effect on
the calibration state of the
sensors should trigger
immediate re-verification of
accuracy before further
use.
5. Any changes in the
environment in which the
instrument is being used,
or changes in the work that
is being performed, should
trigger a resumption of
daily checking.
6. If there is any doubt at any
time as to the accuracy of
the sensors, verify the
accuracy of the sensors by
exposing them to known
concentration test gas
before further use.
Gas detectors used for the
detection of oxygen
deficiencies, flammable gases
and vapors, or toxic
contaminants must be
maintained and operated
properly to do the job they were
designed to do. Always follow
the guidelines provided by the
manufacturer for any gas
detection equipment you use!
If there is any doubt regarding
your gas detector's accuracy,
do an accuracy check! All it
takes is a few moments to verify
whether or not your instruments
are safe to use.
One Button Auto Calibration
While it is only necessary to do
a “bump” test to ensure that the
sensors are working properly,
all current Biosystems gas
detectors offer a one button
auto calibration feature. This
feature allows you to calibrate a
Biosystems gas detector in
about the same time as it takes
to complete a “bump” test. The
use of automatic bump test and
calibration stations can further
simplify the tasks, while
automatically maintaining
records.
Don't take a chance
with your life.
Verify accuracy frequently!
Please read also Biosystems’
application note: AN20010808
“Use of ‘equivalent’ calibration
gas mixtures”. This application
note provides procedures to
ensure safe calibration of LEL
sensors that are subject to
silicone poisoning.
Biosystems website is at:
http://www.biosystems.com
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