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Appendix B Calibration Frequency
Recommendation
One of the most common questions that we are asked
at Honeywell Analytics 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.
Honeywell Analytics is not the only manufacturer to
be asked this question! One of the professional
organizations to which Honeywell Analytics 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. Honeywell Analytics procedures closely
follow these guidelines.
If your operating procedures do not permit daily
checking of the sensors, Honeywell Analytics
recommends the following procedure to establish a
safe and prudent accuracy check schedule for your
Honeywell Analytics 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 Honeywell Analytics gas detectors offer a one
button auto calibration feature. This feature allows
you to calibrate a Honeywell Analytics 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!
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