Honeywell IQ Force Dock Reference Manual page 55

Calibration Frequency Recommendation
Appendix A Calibration Frequency Rec-
ommendation
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. In
fact, most common sensors are designed so that with normal use they will
only lose 5% to 10% of their sensitivity per year.
However, there are a number of reasons why 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". This test is very simple and takes
only a few seconds to accomplish. The safest course of action is to do
a "calibration check" prior to each day's use.
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
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the expected value. For oxygen, the acceptable range is considered to be
±0.5% vol., so 20.4% to 21.4% O2 in ambient clean air or via application
of zero air. Further for oxygen, for application of Honeywell 18.0% O2
balance gases, the reading should again be within ±0.5% vol., so 17.5%
to 18.5% O2.
Lengthening the Intervals between Calibration Checks
We are often asked whether there are any circumstances in which the
period between calibration checks may be lengthened.
One of the professional organizations to which Honeywell Analytics,
formerly Biosystems/Sperian, belongs is the International Safety Equipment
Association (ISEA). The "Instrument Products" group of this organization
has been very active in developing a protocol to clarify the specific
conditions under which the interval between calibration checks may be
lengthened.
A number of leading gas detection equipment manufacturers have
participated in the development of the
ISEA guidelines concerning the recommended frequency and types of
detector performance tests, as well as adoption of the associated standard
terminology. Our procedures closely follow these guidelines.
If your operating procedures do not permit ongoing daily calibration checks,
we recommend the following procedure to establish a safe and prudent
accuracy check schedule for your detectors:
1. During a period of initial use of at least 10 days in the intended
environment, perform a calibration check daily to be sure there is nothing
in the atmosphere, which 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 them.
IQ Force™ Dock Reference Manual Appendix