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Appendix B:
Calibration Frequency
One of the most common
questions we are asked is: "How
often should I calibrate my gas
detector?"
Sensor Reliability and Accuracy
Today's gas sensors are designed
to provide years of reliable
service. However, there are a
number of reasons a sensor may
unexpectedly lose additional
sensitivity or even fail to respond
to gas. Such reasons include
desiccation, poisoning, physical
restriction of airflow, over
exposure, internal leakage, or
mechanical damage due to
physical shock and immersion.
Verification of Accuracy
& Related Terminology
With so many reasons why a
sensor can lose sensitivity and
given the fact that dependable
sensors are critical 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 to ensure
that it is within a manufacturer's
recommended tolerable limits.
This is referred to as a "calibration
check" or" bump test". This test is
very simple and takes only a few
seconds to accomplish. The
safest course of action is to do
a calibration check or bump
test prior to each day's use.
WARNING
The Canadian Standards
Association (CSA) requires the
instrument to undergo
calibration when the displayed
LEL value during a bump test
fails to fall between 100% and
120% of the expected value for
the gas.
It is not necessary to perform a
full calibration (adjustment)
unless readings for LEL and
toxic gases/vapors are outside
of the range of 90% to 120% of
the expected value. For oxygen,
the acceptable range is
considered to be ±0.5% vol., so
20.4% to 21.4% O
in ambient
2
clean air or via application of
zero air. Further for oxygen, for
application of Honeywell
Analytics 18.0% O
balance
2
gases, the reading should again
be within ±0.5% vol., so 17.5%
to 18.5% O
.
2
Lengthening the Intervals
between Calibration Checks
or Bump Tests
The MultiPro has been shipped
with a default calibration interval
of 30 days. The 30-day
calibration interval provides the
IQ Management software with
multiple sensor sensitivity
datapoints required for effective
predictive maintenance
features. If you are not using the
predictive maintenance features
in IQ Management system, or
do not wish to calibrate your
detector as often, Honeywell
Analytics recommends the
detector be calibrated at least
once every 180 days.
Honeywell Analytics
recommends a daily bump test
to ensure that the instrument is
in proper working order.
26
One Button Automatic
Full Calibration and
Calibration Docks
While it is only necessary to do
a calibration check or bump test
to ensure that the sensors are
working properly, all current
Honeywell, and Honeywell
Analytics gas detectors offer a
one button auto full calibration
feature. This feature allows you
to do a full calibration of a gas
detector in about the same time
as it takes to complete a
calibration check or bump test.
The use of calibration docks
can further simplify the tasks,
while automatically maintaining
electronic records of sensor
performance.
Please read also the application
note: 13-366 "Use of
'equivalent' calibration gas
mixtures". This note provides
procedures to ensure safe
calibration of LEL sensors that
are subject to poisoning.
Honeywell Analytics' website is
at
http://www.honeywellanalytics.com/
A complete list of accessories
compatible with the MultiPro
gas detector can be found
there.
.
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