biosystems PhD Lite, Reference Manual

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Chapter 1. Description
1.1 PhD Lite capabilities
The PhD Lite gas detector can be configured to meet a
wide variety of requirements. This chapter provides an
overview of many of the features of the PhD Lite. More
detailed descriptions are contained in the subsequent
chapters of this manual.
1.2 Methods of sampling
The PhD Lite may be used in either diffusion or sample-
draw mode. In either mode, the gas sample must reach
the sensors for the instrument to register a gas reading.
The sensors are located inside of the instrument.
In diffusion mode, the atmosphere being measured
reaches the sensors by diffusing through vents in the
sensor compartment cover. Normal air movements are
enough to carry the sample to the sensors. The sensors
react quickly to changes in the concentrations of the gases
being measured. Diffusion-style operation monitors only
the atmosphere that immediately surrounds the detector.
The PhD Lite can also be used to sample remote locations
with either the hand-aspirated sample-draw kit that is
included with every PhD Lite, or with a motorized
continuous sample draw pump that is available separately.
During remote sampling, the gas sample is drawn into the
sensor compartment through the probe assembly and a
length of tubing.
Use of the sample draw kits is covered in section
2.5.1.
A detailed description of the PhD Lite probe assembly
is given in section 2.5.3.
1.3 Multi-sensor capability
The PhD Lite can be configured to simultaneously monitor
oxygen, combustible gases and vapors and either one or
two toxic gases. Sensors can be added, removed,
changed, and replaced in the field. The PhD Lite
microprocessor and “Smart Sensor” circuitry eliminates
the need for laborious reconfiguration procedures.
Note: It is necessary to verify the accuracy of the PhD
Lite by calibration with known concentration test gas
whenever a change is made to the sensors installed in
the instrument.
Calibration procedures are discussed in detail in
Chapter 4.
The PhD Lite uses electrochemical toxic gas sensors that
have been designed to minimize the effects of common
interfering gases. These sensors provide accurate,
dependable readings for toxic gases commonly
encountered during confined space entry and other
industrial applications. Toxic sensors currently available
for use in the PhD Lite include hydrogen sulfide (H
2
S),
carbon monoxide (CO), sulfur dioxide (SO
2
), phosphine
(PH
3
), ammonia (NH
3
), chlorine (Cl
2
), chlorine dioxide
(ClO
2
), hydrogen cyanide (HCN), nitric oxide (NO) and
nitrogen dioxide (NO
2
).
In addition to sensors designed to measure specific toxic
hazards, Biosystems also offers two different sensors
that allow for the simultaneous detection of both CO and
H
2
S.
The “Duo-Tox” sensor is a dual channel electrochemical
sensor designed to simultaneously detect both carbon
monoxide and hydrogen sulfide. The Duo-Tox allows
one sensor port to be used for the direct detection of both
carbon monoxide and hydrogen sulfide.
For more information on the Duo-Tox sensor see
section 4.3.1.1.
The “CO Plus” sensor is a single channel electrochemical
sensor. The CO Plus is ideal for situations requiring the
use of a single sensor to monitor for both Carbon
Monoxide and Hydrogen Sulfide, but where the user
does not need to know specifically which gas is present.
For more information on the CO Plus sensor see
section 4.3.1.2.
Different measurement units are used depending on the
gas being measured.
Type of Hazard Measurement unit
Oxygen (O2) Percentage by volume
Combustible gas Percentage of lower
explosive limit (%LEL)
All toxic sensors Parts per million (PPM)
Table 1.3. PhD Lite Standard Units of Measurement
Sensor configuration procedures are discussed in
greater detail in Chapter 2.
1.4 Calibration
The PhD Lite detector features fully automatic fresh air
and span calibration.
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.)
Calibration procedures are discussed in detail in
Chapter 4.
Use of these procedures is reserved for authorized
personnel.
1.5 Alarm logic
PhD Lite gas alarms are user-adjustable and may be set
anywhere within the range of the specific sensor type.
When an alarm set point is exceeded a loud audible
alarm sounds, and the bright red LED alarm light flashes.
The procedure for adjusting alarm settings is
covered in section 3.2.2.
1.5.1 Alarm latch
The PhD Lite includes a latching alarm feature that can
be enabled or disabled according to the needs of the
user. When the PhD Lite’s alarm latch is enabled, the