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I. Introduction
This section of the Intoximeters website is designed to offer
users an online step by step guide for calibrating several of our
most commonly used instruments. This tool offers definitions of the
key terms and an animated Step by Step procedure to help you
properly calibrate your instrument(s).
Although this information appears in the instrument manual, some
testing programs only allow certain qualified operators to perform
accuracy checks and calibrations. For
example, the DOT regulations for Workplace Testing require that
"calibration of the EBT are performed by the manufacturer or a
maintenance representative certified by the devices manufacturer or a
state health agency or other appropriate state agency." .
Before performing calibrations, make sure that you are qualified to
perform this function under the rules of your program.
II. Quality Assurance Plan
All breath alcohol testing programs should follow criteria set forth
in a Quality Assurance Plan. The QAP may designate the types of
standards that may to be used to perform calibrations and accuracy
checks, and the minimum intervals for performing calibrations and/or
accuracy checks. The QAP may specify the acceptable tolerance to
determine if the instrument is in proper calibration (often + 10%
in screening applications). Recommended or required inspection and
maintenance intervals may also be part of the QAP. Intoximeters
has developed a QAP approved by NHTSA (National Highway Traffic Safety
Administration) for instruments used for US DOT testing purposes. These
guidelines were designed specifically for the DOT testing program. It is
important to understand that the QAP is designed for a specific
testing program. The safeguards built into the testing protocol and the
requirement for testing will help define the QAP guidelines. For your
program, the Operators manual offers some basic guidelines to help
develop your protocols but you can consult a local authority or contact
Intoximeters for more specific information.
III. Methods for performing Accuracy Checks
Breath alcohol testing instruments are calibrated and checked for
accuracy utilizing an ethanol standard with a known alcohol
concentration. There are two types of standards that are widely
accepted and commonly used:
- Wet Bath Standards
- Dry Gas Standards
The value of the Standard used is usually determined by the QAP.
For example, law enforcement agencies that arrest drunk drivers based on
a legal limit of 0.100 BrAC will typically check their evidential
breath alcohol testing devices with a standard that has a target value
at or near 0.100 BrAC. States using 0.080 as the legal limit may
utilize 0.080 standards. The NHTSA (National Highway Traffic
Safety Administration) approved Intoximeters QAP required to be used in
conjunction with US DOT workplace testing designates standards with a
stated equivalent value between 0.020 and 0.040.
Fuel Cell sensors are linear output devices and can thus be
calibrated for the dynamic range of readings at any point within that
range. Similarly, these devices can also be checked at any point to
determine that they are in calibration throughout the entire range of
readings. As a result, an instrument calibrated at one level will also
be calibrated for other applications that have a need to check samples
for yet another level.
IV. Definition of Terms
Accuracy Check (also called "Calibration Check", or
"Proficiency Test".)
Checking an instrument for accuracy against a known
standard. This process is much the same as a running a sample
on a subject, but in this case the operator knows what result the
instrument should produce . The only other difference is that on a
Accuracy Check the sample should be taken manually, while the gas
flow is still commencing, but after several seconds of the flow from
the gas standard.
The results of an accuracy check must fall within an acceptable
range for the instrument to be considered "in
calibration". An accuracy check result outside the
acceptable tolerance may throw into doubt the validity of test
results and as a result, a calibration is suggested following a
failed accuracy check. Once the calibration has been completed an
accuracy check should be run to verify that the calibration was
successful.
Calibration
Setting (adjusting) an instrument's sensitivity to properly
report the known value of a standard. All calibrations should be
followed by an Accuracy Check to ensure that the adjustment is
correct.
- Standard (also called Ethanol Standard)
A solution of ethanol in water (wet standard) or mixture of
pressurized gas, usually ethanol in nitrogen (dry standard)
certified to produce a sample containing a predictable alcohol
concentration.
- Expected Value or Target Value of the Standard
The result expected to be reported from the
standard at the time of the accuracy check or calibration.
- Quality Assurance Plan (QAP)
A set of criteria established by the manufacturer of the
instrument and/or a testing program manager that establishes
parameters for conducting accuracy checks and calibrations under a
given testing program.
A record of accuracy checks and calibrations performed on a
specific breath alcohol testing instrument.
V. Tutorial for performing an Accuracy Check or Calibration
Select the process you wish to learn more about:
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