biosystems PhD Lite, Reference Manual

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Chapter 4. Calibration
The PhD Lite multi-gas detector has been designed for
easy calibration. A single control, the on/off MODE
button, can be used to initiate the automatic calibration
sequence and to automatically make calibration
adjustments.
Manual and single-sensor calibration procedures can
also be initiated by using the navigation arrows located
on the instrument.
Note: If a sensor has just been replaced, it must be
allowed to stabilize prior to initiating any of the
calibration subroutines detailed below. See section
6.1.1 for further details concerning sensor
stabilization requirements.
The PhD Lite’s automatic calibration features are
described in section 4.4 below.
The PhD Lite’s manual calibration features are
described in section 4.5 below.
4.1 Verification of accuracy
Verification of accuracy is a two step procedure.
Step one is to take the PhD Lite to an area where the
atmosphere is known to be fresh and check the
readings. If the readings differ from those expected in
fresh air, then a fresh air calibration adjustment must be
made.
Step two is to make sure the sensors are accurate by
exposing them to a test gas of known concentration and
noting the sensor response. This procedure is known
as a functional (bump) test and is covered in section
4.6. Oxygen readings are considered to be accurate
when the display is within 0.5%/volume of the expected
concentration as given on the calibration gas cylinder.
LEL and toxic readings are considered accurate when
they are between 90%* and 120% of the expected value
as given on the calibration gas cylinder. If readings are
accurate, there is no need to adjust your gas detector.
If the readings are inaccurate, the instrument must be
span calibrated before further use.
* * 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.
The accuracy of the PhD Lite
should be checked periodically with known
concentration calibration gas. Failure to check
accuracy can lead to inaccurate and potentially
dangerous readings. (The Canadian Standards
Association (CSA) requires an accuracy check
using known concentration calibration gas prior to
each day’s use.)
Always check the expiration
date on calibration gas cylinder(s) prior to use.
Expired calibration gas can lead to inaccurate and
potentially dangerous readings.
Biosystems offers calibration kits and long lasting
cylinders of test gas specifically developed for easy
PhD Lite calibration.
Use of non-standard calibration
gas and/or calibration kit components when
calibrating the PhD Lite can lead to inaccurate and
potentially dangerous readings, and may void the
standard Biosystems warranty.
Customers are strongly urged to use only
Biosystems calibration materials when calibrating
the PhD Lite.
4.2 Effect of contaminants on PhD Lite sensors
The atmosphere in which the PhD Lite is used can have
lasting effects on the sensors. Sensors may suffer
losses in sensitivity leading to degraded performance if
exposed to certain substances.
There are three basic types of sensors that may be
installed in the PhD Lite: galvanic oxygen, catalytic hot-
bead combustible gas, and electrochemical toxic. Each
type of sensor uses a slightly different detection
principle, so the kinds of conditions that affect the
accuracy of the sensors vary from one type of sensor to
the next.
4.2.1 Effects of contaminants on oxygen sensors
Oxygen sensors may be affected by prolonged
exposure to "acid" gases such as carbon dioxide. The
oxygen sensors used in Biosystems instruments are not
recommended for continuous use in atmospheres
containing more than 25% CO
2
.
See Appendix B for cross-sensitivity data for the
sensors used in the PhD Lite.
4.2.2 Effects of contaminants on combustible
sensors
Combustible sensors will be adversely affected by
exposure to substances containing volatile silicone,
which is found in many commercial formulations such as
spray lubricants, plastic mold(ing) release agents,
waterproofing agents, heat transfer fluids, and is
released during the cure of silicone-based caulks and
rubbers (RTV). Other combustible gas sensor poisons
and inhibitors include, but are not limited to: tetraethyl
lead as in "leaded" gasoline grades (aviation "low-lead"
fuel), halogenated hydrocarbons such as Freons
TM
,
other such refrigerants and solvents such as 1,1,1-
trichloroethane, perchloroethylene and methylene
chloride. Chronic exposures to high concentrations
(above human health and safety levels) of hydrogen
sulfide (H
2
S) and Phosphine (PH
3
) can also impair
combustible sensor performance.
Note: Damage to combustible gas sensors incurred
by exposure to known sensor poisons such as
silicones, tetra-ethyl lead, and/or other substances
may (at the discretion of Biosystems’ Instrument
Service Department) void Biosystems’ Standard
Warranty as it applies to the replacement of